What the Science Shows


  • Since 2007, researchers have increased their efforts to find a cause for the CCD phenomena. The issue is diverse and complex, with many factors potentially contributing to the cause including parasites, pesticides and stress. However, pesticides have consistently been implicated as a key issue in pollinator declines, not only through immediate bee deaths, but also through sublethal exposure causing changes in bee reproduction, navigation and foraging. These chemicals have implications for bees, other pollinators like bumblebees and hummingbirds, as well as organisms that are beneficial to the environment. The research below seeks to highlight the impact of pesticides on these organisms and their role in exacerbating susceptibility to parasites and viruses.

    Pesticide impacts on bees

    • Assessing Honey Bee (Hymenoptera: Apidae) Foraging Populations and the Potential Impact of Pesticides on Eight U.S. Crops
      • In this study, published in the Journal of Economic Entomology, researchers assessed changes, from 2009-2010, in the field force populations of 9–10 colonies at one location per crop on each of the eight crops by counting departing foragers leaving colonies at regular intervals during the respective crop blooming periods. The number of frames of adult bees was counted before and after bloom period. For pesticide analysis, researchers collected dead and dying bees near the hives, returning foragers, crop flowers, trapped pollen, and corn-flowers associated with the cotton crop. The number of departing foragers changed over time in all crops except almonds; general patterns in foraging activity included declines (cotton), noticeable peaks and declines (alfalfa, blueberries, cotton, corn, and pumpkins), and increases (apples and cantaloupes). The number of adult bee frames increased or remained stable in all crops except alfalfa and cotton. A total of 53 different pesticide residues were identified in samples collected across eight crops. Hazard quotients (HQ) were calculated for the combined residues for all crop-associated samples and separately for samples of dead and dying bees. A decrease in the number of departing foragers in cotton was one of the most substantial crop-associated impacts and presented the highest pesticide risk estimated by a summed pesticide residue HQ.
    • Differential responses of Apis mellifera heat shock protein genes to heat shock, flower-thinning formulations, and imidacloprid
      • In this study, published in the Journal of Asia-Pacific Entomology, researchers used mRNA levels of heat shock protein (HSP) genes as molecular markers of response to three types of external stress: thermal shock, flower-thinning agents, and pesticides. When worker bees were exposed to temperatures of 4, 27, 40, 45 and 50°C for 1 h, decreased survival occurred only at 50°C. Further, increased levels of hsp70, grp78, and hsp90, but not hsp40, were detected, and reached a maximum at 45C, particularly in the hypopharyngeal glands and fat bodies. Artificial ingestion of two flower-thinning agents containing either 0.1% boron and zinc, or 1% sulfur increased hsp70 and grp78 levels at different rates without affecting hsp40 and hsp90 levels, and had no effect on workers’ mortality. However, ingestion of imidacloprid solution (0.5–50 ppm) increased mortality in workers and decreased the levels of hsp70, grp78, and hsp90 in a dose-dependent manner. The results showed that the responses of honey bees to each hsp are differential and highly specific to different stresses. This study suggests that the unique expression profiles of hsps can be used as valuable tools for monitoring the susceptibility of honey bees to various environmental impacts.
    • Bee declines driven by combined stress from parasites, pesticides, and lack of flowers
      • In this review, published in Science, the authors recognize that bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined, bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple, interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future.
    • Chronic exposure to neonicotinoids increases neuronal vulnerability to mitochondrial dysfunction in the bumblebee (Bombus terrestris)
      • In this 2015 study, published in The Journal of the Federation of American Studies for Experimental Biology, researchers show that bumblebees (Bombus terrestris audax) fed field levels [10 nM, 2.1 ppb (w/w)] of neonicotinoid accumulate between 4 and 10 nM in their brains within 3 days. Acute (minutes) exposure of cultured neurons to 10 nM clothianidin, but not imidacloprid, causes a nicotinic acetylcholine receptor-dependent rapid mitochondrial depolarization. However, a chronic (2 days) exposure to 1 nM imidacloprid leads to a receptor-dependent increased sensitivity to a normally innocuous level of acetylcholine, which now also causes rapid mitochondrial depolarization in neurons. Finally, colonies exposed to this level of imidacloprid show deficits in colony growth and nest condition compared with untreated colonies. These findings provide a mechanistic explanation for the poor navigation and foraging observed in neonicotinoid treated bumblebee colonies.
    • Field realistic doses of pesticide imidacloprid reduce bumblebee pollen foraging efficiency
      • This 2014 study, published in the journal Ecotoxicology, reveals that near infinitesimal exposure to neonicotinoids reduces bees ability to gather food by 57%. “Whilst the nectar foraging efficiency of bees treated with imidacloprid was not significantly different than that of control bees, treated bees brought back pollen less often than control bees (40% of trips vs 63% trips, respectively) and, where pollen was collected, treated bees brought back 31% less pollen per hour than controls. This study demonstrates that field-realistic doses of these pesticides substantially impacts on foraging ability of bumblebee workers when collecting pollen, and we suggest that this provides a causal mechanism behind reduced queen production in imidacloprid exposed colonies.” Read more onThe Daily News.
    • Four Common Pesticides, Their Mixtures and a Formulation Solvent in the Hive Environment Have High Oral Toxicity to Honey Bee Larvae
      • This 2014 study, published in PLOS ONE, demonstrates the chronic oral and mixture toxicity of common pesticides at hive levels to honey bees at the larval stage. Most notable are the chronic larval toxicities of the fungicide chlorothalonil and its synergistic combinations with frequently used in-hive miticides, and the unexpected high toxicity of the formulation ingredient N-methyl-2-pyrrolidone. Considering the extensive detection of chlorothalonil and its coexistence with other pesticides in diverse combinations especially in hive pollen and wax, and its substantial larval toxicity alone and in mixtures shown here, the application of this and other fungicides during crop bloom cannot be presumed innocuous to pollinating honey bees. The study scientists stress that given the critical sensitivity of larvae to chlorothalonil and its complex interactions with other pesticides, the potential impacts of fungicides on colony survival and development need further investigation. They add that in the more complex milieu of this social insect and its aging hive environment, pesticides, formulation additives and their resulting mixtures may have greater long-term impacts on colony health than previously considered. Consequently, the scope of pesticide risk assessment for non-target honey bees should be expanded from the present emphasis on acute toxicity of individual pesticides to a priority for assessment of chronic and mixture toxicities that incorporate fungicides, other pesticide pollutants and their ‘inert’ ingredients.
    • Impacts of a neonicotinoid, neonicotinoid–pyrethroid premix, and anthranilic diamide insecticide on four species of turf-inhabiting beneficial insects
      • In this 2014 study, published in Ecotoxicology, researchers compared the impact of a neonicotinoid (clothianidin), a premix (clothianidin + bifenthrin), and an anthranilic diamide (chlorantraniliprole), the main insecticide classes used for multiple targeting, on four species of beneficial insects: Harpalus pennsylvanicus, an omnivorous ground beetle, Tiphia vernalis, an ectoparasitoid of scarab grubs, Copidosoma bakeri, a polyembryonic endoparasitoid of black cutworms, and Bombus impatiens, a native bumble bee. Ground beetles that ingested food treated with clothianidin or the premix suffered high mortality, as did C. bakeri wasps exposed to dry residues of those insecticides. Exposure to those insecticides on potted turf cores reduced parasitism by T. vernalis. Bumble bee colonies confined to forage on white clover (Trifolium repens L.) in weedy turf that had been treated with clothianidin or the premix had reduced numbers of workers, honey pots, and immature bees. Premix residues incapacitated H. pennsylvanicus and C. bakeri slightly faster than clothianidin alone, but otherwise we detected no synergistic or additive effects. Chlorantraniliprole had no apparent adverse effects on any of the beneficial species. Implications for controlling turf pests with least disruption of non-target invertebrates are discussed.
    • Cytotoxic effects of thiamethoxam in the midgut and malpighian tubules of Africanized Apis mellifera (Hymenoptera: Apidae)
      • In this 2014 study, published in Microscopy Research and Technique, researchers aimed to analyze the effects of thiamethoxam in the midgut and Malpighian tubule cells of Africanized Apis mellifera. Newly emerged workers were exposed until 8 days to a diet containing a sublethal dose of thiamethoxam. The bees were dissected and the organs were processed for transmission electron microscopy. The results showed that thiamethoxam is cytotoxic to midgut and Malpighian tubules. In the midgut, the damage was more evident in bees exposed to the insecticide on the first day. On the eighth day, the cells were ultrastructurally intact suggesting a recovery of this organ. The Malpighian tubules showed pronounced alterations on the eighth day of exposure of bees to the insecticide. This study demonstrates that the continuous exposure to a sublethal dose of thiamethoxam can impair organs that are used during the metabolism of the insecticide.
    • Chronic impairment of bumblebee natural foraging behaviour induced by sublethal pesticide exposure
      • In this 2014 study, published in Functional Ecology, researchers examined how the day-to-day foraging patterns of bumblebees (Bombus terrestris) were affected when exposed to either a neonicotinoid (imidacloprid) and/or a pyrethroid (λ-cyhalothrin) independently and in combination over a four-week period. This is the first study to provide data on the impacts of combined and individual pesticide exposure on the temporal dynamics of foraging behaviour in the field over a prolonged period of time. Their results show that neonicotinoid exposure has both acute and chronic effects on overall foraging activity. Whilst foragers from control colonies improved their pollen foraging performance as they gained experience, the performance of bees exposed to imidacloprid became worse: chronic behavioural impairment. They also found evidence suggesting that pesticide exposure can change forager preferences for the flower types from which they collect pollen. These findings highlight the importance of considering prolonged exposure (which happens in the field) when assessing the risk that pesticides pose to bees. The effects of chronic pesticide exposure could have serious detrimental consequences for both colony survival and also the pollination services provided by these essential insect pollinators.
    • Chronic Exposure of Imidacloprid and Clothianidin Reduce Queen Survival, Foraging, and Nectar Storing in Colonies of Bombus impatiens
      • In this 2014 study, published in PLOS ONE, caged queenright colonies of Bombus impatiens Cresson, were fed treatments imidacloprid and clothianidin that overlapped the residue levels found in pollen and nectar of many crops and landscape plants, which have higher residue levels than seed-treated crops. Researchers ultimately found that feeding on imidacloprid and clothianidin can cause changes in behavior (reduced worker movement, consumption, wax pot production, and nectar storage) that result in detrimental effects on colonies (queen survival and colony weight). Wild bumblebees depending on foraging workers can be negatively impacted by chronic neonicotinyl exposure at 20 ppb.
    • Sub-lethal exposure to neonicotinoids impaired honey bees winterization before proceeding to colony collapse disorder
      • This 2014 study, published in the Bulletin of Insectology, undercuts chemical industry arguments that neonicotinoids are not the primary contribute factor in Colony Collapse Disorder (CCD).The results find that hives exposed to low doses of two neonicotinoid pesticides—imidacloprid and clothianidin—do not recover from over winter losses from which control hives quickly rebound. “It is imperative to emphasize that while pathogen infections are common and serious diseases found in honey bees that often lead to colony death, the post-mortem examinations of the pathogen- caused dead colonies are vastly different to those suffered from CCD.One of the defining symptomatic observations of CCD colonies is the emptiness of hives…. [Thus] the absence of dead bees in the neonicotinoid-treated colonies is remarkable and consistent with CCD symptoms.”
    • Pesticide residue and bees - a risk assessment
      • This 2014 study, published in the journal PLoS One provides a comprehensive evaluation of risks under current exposure conditions using data from recent residue surveys and toxicity of pesticides to honey and bumble bees. "Whilst overall risks appear to be low, our analysis indicates that residues of pyrethroid and neonicotinoid insecticides pose the highest risk by contact exposure of bees with contaminated pollen. However, the synergism of ergosterol inhibiting fungicides with those two classes of insecticides results in much higher risks in spite of the low prevalence of their combined residues. Risks by ingestion of contaminated pollen and honey are of some concern for systemic insecticides, particularly imidacloprid and thiamethoxam, chlorpyrifos and the mixtures of cyhalothrin and ergosterol inhibiting fungicides. More attention should be paid to specific residue mixtures that may result in synergistic toxicity to bees."
    • Honey bees, neonicotinoids and bee incident reports: the Canadian situation
      • In this 2013 study, published in Pest Management Science, researchers summarize honey bee incident report data obtained from the Canadian Pest Management Regulatory Agency (PMRA). In Canada, there were very few honey bee incidents reported in 2007–2011 and data were not collected prior to 2007. In 2012, a significant number of incidents were reported in the province of Ontario, where exposure to neonicotinoid dust during planting of corn was suspected to have caused the incident in up to 70% of cases. Most of these incidents were classified as ‘minor’ by the PMRA, and only six cases were considered ‘moderate’ or ‘major’. In that same year, there were over three times as many moderate or major incidents due to older non-neonicotinoid pesticides, involving numbers of hives or bees far greater than the number of moderate or major incidents suspected to be due to neonicotinoid poisoning. These data emphasize that, while exposure of honey bees to neonicotinoid-contaminated dust during corn planting needs to be mitigated, other pesticides also pose a risk.
    • Brain morphophysiology of Africanized Bee Apis mellifera exposed to sublethal doses of imidacloprid
      • This 2013 study, published in Archives of Environmental Contamination and Toxicology, demonstrated that imidacloprid causes changes to the brain in Africanized bees, particularly to the optic lobes of the brain, disrupting their visual system and impairing their learning capacity. "The organs of both control bees and bees exposed to insecticide were subjected to morphological, histochemical and immunocytochemical analysis after exposure to imidacloprid, respectively, for 1, 3, 5, 7, and 10 days. In mushroom bodies of bees exposed to imidacloprid concentrations of LD50/10 and in optic lobes of bees exposed to imidacloprid concentrations of LD50/10, LD50/100, and LD50/50, we observed the presence of condensed cells. The Feulgen reaction revealed the presence of some cells with pyknotic nuclei, whereas Xylidine Ponceau stain revealed strongly stained cells. These characteristics can indicate the occurrence of cell death. Furthermore, cells in mushroom bodies of bees exposed to imidacloprid concentrations of LD50/10 appeared to be swollen. Cell death was confirmed by immunocytochemical technique. Therefore, it was concluded that sublethal doses of imidacloprid have cytotoxic effects on exposed bee brains and that optic lobes are more sensitive to the insecticide than other regions of the brain."
    • Fatal powdering of bees in flight with particulates of neonicotinoids seed coating and humidity implication
      • This 2012 study, published in the Journal of Applied Entomology, examined the effect of direct aerial powdering on foragers in free flight near the drilling machine. Bees were conditioned to visit a dispenser of sugar solution whilst a drilling machine was sowing corn along the flight path. Samples of bees were captured on the dispenser, caged and held in the laboratory. Chemical analysis showed some hundred nanograms of insecticide per bee. Nevertheless, caged bees, previously contaminated in flight, died only if kept in conditions of high humidity. After the sowing, an increase in bee mortality in front of the hives was also observed. Spring bee losses, which corresponded with the sowing of corn-coated seed, seemed to be related to the casual encountering of drilling machine during foraging flight across the ploughed fields.
    • Neonicotinoid pesticide reduces bumble bee colony growth and queen production
      • This 2012 study, published in Science, "exposed colonies of the bumble bee Bombus terrestris in the laboratory to field-realistic levels of the neonicotinoid imidacloprid, then allowed them to develop naturally under field conditions. Treated colonies had a significantly reduced growth rate and suffered an 85% reduction in production of new queens compared with control colonies. Given the scale of use of neonicotinoids, we suggest that they may be having a considerable negative impact on wild bumble bee populations across the developed world."
    • Effects of imidacloprid, a neonicotinoid pesticide, on reproduction in worker bumble bees
      • This 2012 study, published in Ecotoxicology, "exposed queenless microcolonies of worker bumble bees, Bombus terrestris, to a range of dosages of dietary imidacloprid between zero and 125μgL(-1) and examined the effects on ovary development and fecundity… Imidacloprid reduced feeding on both syrup and pollen but, after controlling statistically for dosage, microcolonies that consumed more syrup and pollen produced more brood. We therefore speculate that the detrimental effects of imidacloprid on fecundity emerge principally from nutrient limitation imposed by the failure of individuals to feed. "
    • Exposure to sublethal doses of fipronil and thiacloprid highly increases mortality of honeybees previously infected by Nosema ceranae
      • This 2011 study, published in the journal PLoS ONE, explores the effect of Nosema ceranae infection on honeybee sensitivity to sublethal doses of the insecticides fipronil and thiacloprid. Honeybee mortality and insecticide consumption were analyzed daily and the intestinal spore content was evaluated 20 days after infection. A significant increase in honeybee mortality was observed when N. ceranae-infected honeybees were exposed to sublethal doses of insecticides. The synergistic effect of N. ceranae and insecticide on honeybee mortality, however, did not appear strongly linked to a decrease of the insect detoxification system. These data support the hypothesis that the combination of the increasing prevalence of N. ceranae with high pesticide content in beehives may contribute to colony depopulation.
    • Neonicotinoid insecticides translocated in guttated droplets of seed-treated maize and wheat: a threat to honeybees?
      • This 2011 study, published in Apidologie, demonstrates that guttated water of plants germinated from seeds dressed with neonicotinoids contains neonicotinoids. Maize seeds treated with clothianidin (Poncho® 0.5mg/seed and Poncho® Pro 1.25mg/seed) resulted in neonicotinoid concentrations up to 8,000ngmL−1 in the guttated fluid. This concentration decreases rapidly, but remained detectable over several weeks. Seeds treated with Poncho® Pro did not result in higher concentrations in guttated droplets in the first stages of plant development, but the concentration decreased more slowly. Triticale seed treated with imidacloprid contained small quantities of this active agent (up to 13ngmL−1) in the guttated fluid the following spring after overwintering.
    • Sub-lethal effects of pesticide residues in brood comb on worker honey nee (Apis mellifera) development and longevity
      • This 2011 study, published in the journal PLoS ONE, examines the "possible direct and indirect effects of pesticide exposure from contaminated brood comb on developing worker bees and adult worker lifespan. Results demonstrate sub-lethal effects on worker honey bees from pesticide residue exposure from contaminated brood comb. Sub-lethal effects, including delayed larval development and adult emergence or shortened adult longevity, can have indirect effects on the colony such as premature shifts in hive roles and foraging activity."
    • Rapid analysis of neonicotinoid insecticides in guttation drops of corn seedlings obtained from coated seeds
      • This 2011 study, published in the Journal of Environmental Monitoring, examined guttation drops of corn plants obtained from commercial seeds coated with thiamethoxam, clothianidin, imidacloprid and fipronil have been analyzed. "The young plants grown both in pots – in greenhouse – and in open field from coated seeds, produced guttation solutions containing high levels of the neonicotinoid insecticides (up to 346 mg L-1 for imidacloprid, 102 mg L-1 for clothianidin and 146 mg L-1 for thiamethoxam). These concentration levels may represent lethal doses for bees that use guttation drops as a source of water. The neonicotinoid concentrations in guttation drops progressively decrease during the first 10–15 days after the emergence of the plant from the soil. Otherwise fipronil, which is a non-systemic phenylpyrazole insecticide, was never detected into guttation drops. Current results confirm that the physiological fluids of the corn plant can effectively transfer neonicotinoid insecticides from the seed onto the surface of the leaves, where guttation drops may expose bees and other insects to elevated doses of neurotoxic insecticides."
    • Risk assessment for side-effects of neonicotinoids against bumblebees with and without impairing foraging behavior.
      • This 2010 study, published in Ecotoxicology, examined "the development of a new bioassay to assess the impact of sublethal concentrations on the bumblebee foraging behavior under laboratory conditions. In general, the experiments showed that concentrations that may be considered safe for bumblebees can have a negative influence on their foraging behavior. Therefore it is recommended that behavior tests should be included in risk assessment tests for highly toxic pesticides because impairment of the foraging behavior can result in a decreased pollination, lower reproduction and finally in colony mortality due to a lack of food."
    • Pesticides and honey bee toxicity – USA
      • This 2010 study, published in Apidologie, "examines pesticides applied to crops, pesticides used in apiculture and pesticide residues in hive products. Authors discuss the role that pesticides and their residues in hive products may play in colony collapse disorder and other colony problems. Although no single pesticide has been shown to cause colony collapse disorder, the additive and synergistic effects of multiple pesticide exposures may contribute to declining honey bee health."
    • High levels of miticides and agrochemicals in North American apiaries: Implications for honey bee health
      • This 2010 study, published in the journal PLoS ONE, conducted "A broad survey of pesticide residues... on samples from migratory and other beekeepers across 23 states, one Canadian province and several agricultural cropping systems during the 2007–08 growing seasons. The 98 pesticides and metabolites detected in mixtures up to 214 ppm in bee pollen alone represents a remarkably high level for toxicants in the brood and adult food of this primary pollinator. This represents over half of the maximum individual pesticide incidences ever reported for apiaries. While exposure to many of these neurotoxicants elicits acute and sublethal reductions in honey bee fitness, the effects of these materials in combinations and their direct association with CCD or declining bee health remains to be determined." See: Daily News Blog.
    • Interactions between Nosema microspores and a neonicotinoid weaken honeybees (Apis mellifera)
      • This 2010 study, published in Environmental Microbiology, examines "Global pollinators, like honeybees, are declining in abundance and diversity, which can adversely affect natural ecosystems and agriculture. The authors tested the current hypotheses describing honeybee losses as a multifactorial syndrome, by investigating integrative effects of an infectious organism and an insecticide on honeybee health. Study demonstrated that the interaction between the microsporidia Nosema and a neonicotinoid (imidacloprid) significantly weakened honeybees. In the short term, the combination of both agents caused the highest individual mortality rates and energetic stress. This provides the first evidences that interaction between an infectious organism and a chemical can also threaten pollinators, interactions that are widely used to eliminate insect pests in integrative pest management."
    • Toxicities of fipronil enantiomers to the honeybee Apis mellifera L. and enantiomeric compositions of fipronil in honey plant flowers.
      • This 2010 study, published in Environmental Contamination and Toxicology, examined fipronil, a "chiral phenylpyrazole insecticide that is effective for control of a wide range of agricultural and domestic pests at low application rates. Wide application of fipronil also causes poisoning of some nontarget insects, such as honeybees. In the present study, toxicities of fipronil enantiomers and racemate to the honeybee Apis mellifera L. were determined to examine whether using formulations of single or enriched fipronil enantiomer is a possible option to reduce risks to bees. The results indicate that it is unlikely that use of formulations with single or enriched fipronil enantiomer would reduce the risk that fipronil poses to honeybees. Improved fipronil application practices (based on safest timing and bloom conditions) and reduction of overall fipronil usage seem to be more realistic options."
    • Is Apis mellifera more sensitive to insecticides than other insects?
      • This 2010 study, published in Pest Management Science, summarized "insecticide toxicity data between A. mellifera and other insects to determine the relative sensitivity of honey bees to insecticides. It was found that, in general, honey bees were no more sensitive than other insect species across the 62 insecticides examined. In addition, honey bees were not more sensitive to any of the six classes of insecticides (carbamates, nicotinoids, organochlorines, organophosphates, pyrethroids and miscellaneous) examined. While honey bees can be sensitive to individual insecticides, they are not a highly sensitive species to insecticides overall, or even to specific classes of insecticides. However, all pesticides should be used in a way that minimizes honey bee exposure, so as to minimize possible declines in the number of bees and/or honey contamination."
    • Exposure to pesticides at sublethal level and their distribution within a honey bee (Apis mellifera) colony.
      • This 2010 study, published in the Bulletin of Environmental Contamination and Toxicology, exposed honey bee colonies "to pesticides used in agriculture or within bee hives by beekeepers: coumaphos; diazinon; amitraz or fluvalinate. Samples of bee workers, larvae and royal jelly were analysed. Amitraz residues in all sampled material were below the level of detection of 10 ng/g. Diazinon was not detected in any of the analysed samples. The large quantities of fluvalinate found in bee heads and larvae, the coumaphos residues in royal jelly, and additional potential sub-lethal effects on individual honey bees or brood are discussed."
    • Residues of pesticides in honeybee (Apis mellifera carnica) bee bread and in pollen loads from treated apple orchards.
      • This 2010 study, published in Bulletin of Environmental Contamination and Toxicology, placed honey bee (Apis mellifera carnica) colonies in two apple orchards treated with the insecticides diazinon and thiacloprid and the fungicide difenoconazole in accordance with a Protection Treatment Plan in the spring of 2007. "The residue of diazinon in pollen loads 10 days after orchard treatment was 0.09 mg/kg, and the same amount of residue was found in bee bread 16 days after treatment. In pollen loads 6 days after application 0.03 mg/kg of thiacloprid residues and 0.01 mg/kg of difenoconazole were found on the first day after application. Possible sub-lethal effects on individual honey bees and brood are discussed."
    • A meta-analysis of experiments testing the effects of a neonicotinoid insecticide (imidacloprid) on honey bees
      • This 2010 study, published in Ecotoxicology provides a meta-analysis of "fourteen published studies of the effects of imidacloprid on honey bees under laboratory and semi-field conditions that comprised measurements on 7073 adult individuals and 36 colonies, fitted dose–response relationships [which] estimate that trace dietary imidacloprid at field-realistic levels in nectar will have no lethal effects, but will reduce expected performance in honey bees by between 6 and 20%. Statistical power analysis showed that published field trials that have reported no effects on honey bees from neonicotinoids were incapable of detecting these predicted sublethal effects with conventionally accepted levels of certainty. These findings raise renewed concern about the impact on honey bees of dietary imidacloprid, but because questions remain over the environmental relevance of predominantly laboratory-based results, I identify targets for research and provide procedural recommendations for future studies"
    • The impact of neonicotinoid insecticides on bumblebees, Honey bees and other non-target invertebrates
      • This 2009 report, published by BugLife,, reviews existing approvals research and independent research on the effects of neonicotinoid pesticides on Honey bees, bumblebees and other non-target invertebrates, and investigates the current approvals mechanism and its standards.
    • Subchronic exposure of honeybees to sublethal doses of pesticides: effects on behavior.
      • This 2009 study, published in Environmental Toxicology and Chemistry conducted laboratory bioassays "to evaluate the effects on honeybee behavior of sublethal doses of insecticides chronically administered orally or by contact. After exposure to fipronil, acetamiprid or thiamethoxam, behavioral functions of honeybees were tested on day 12. Fipronil, used at the dose of 0.1 ng/bee, induced mortality of all honeybees after one week of treatment. In the olfactory conditioning paradigm, fipronil-treated honeybees failed to discriminate between a known and an unknown odorant. Thiamethoxam by contact induced either a significant decrease of olfactory memory 24 h after learning at 0.1 ng/bee or a significant impairment of learning performance with no effect on memory at 1 ng/bee. The only significant effect of acetamiprid (administered orally, 0.1 microg/bee) was an increase in responsiveness to water. Data on the intrinsic toxicity of the compounds after chronic exposure have to be taken into account for evaluation of risk to honeybees in field conditions."
    • Translocation of Neonicotinoid Insecticides From Coated Seeds to Seedling Guttation Drops: A Novel Way of Intoxication for Bees
      • This 2009 study, published in Ecotoxicology, examine the contamination of guttation droplets which bees are regularly exposed to: "Although neonicotinoid systemic insecticides used for seed coating of agricultural crops were suspected as possible reason, studies so far have not shown the existence of unquestionable sources capable of delivering directly intoxicating doses in the Þelds. Guttation is a natural plant phenomenon causing the excretion of xylem ßuid at leaf margins. Here, we show that leaf guttation drops of all the corn plants germinated from neonicotinoid-coated seeds contained amounts of insecticide constantly higher than 10 mg/l, with maxima up to 100 mg/l for thiamethoxam and clothianidin, and up to 200 mg/l for imidacloprid. The concentration of neonicotinoids in guttation drops can be near those of active ingredients commonly applied in Þeld sprays for pest control, or even higher. When bees consume guttation drops, collected from plants grown from neonicotinoid-coated seeds, they encounter death within few minutes."
    • Effects of sublethal concentrations of bifenthrin and deltamethrin on fecundity, growth, and development of the honeybee Apis mellifera ligustica
      • This 2009 study, published in Environmental Contamination and Toxicology, examined bifenthrin and deltamethrin whichhave been widely used as pesticides in agriculture and forestry and are becoming an increasing risk to honeybees. "The honeybee, Apis mellifera ligustica, is widely recognized as a beneficial insect of agronomic, ecological, and scientific importance. It is important to understand what effects these chemicals have on bees. Effects of two pesticides at sublethal concentrations on fecundity, growth, and development of honeybees were examined with the feeding method for a three-year period (2006–2008). It was shown that both bifenthrin and deltamethrin significantly reduced bee fecundity, decreased the rate at which bees develop to adulthood, and increased their immature periods. The toxicity of bifenthrin and deltamethrin on workers of Apis mellifera ligustica was also assessed, and the results from the present study showed that the median lethal effects of bifenthrin and deltamethrin were 16.7 and 62.8?mg/L, respectively." See Daily News Blog.
    • Synergistic interactions between in-hive miticides in Apis mellifera
      • This 2009 study published in the Journal of Economic Entomology, examined the varroa mite, Varroa destructor Anderson & Trueman, " a devastating pest of honey bees, Apis mellifera L., that has been primarily controlled over the last 15 yr with two in-hive miticides: the organophosphate coumaphos (Checkmite+), and the pyrethroid tau-fluvalinate (Apistan). In this laboratory study, the authors observed a large increase in the toxicity of tau-fluvalinate to 3-day-old bees that had been treated previously with coumaphos, and a moderate increase in the toxicity of coumpahos in bees treated previously with tau-fluvalinate. The observed synergism may result from competition between miticides. These results suggest that honey bee mortality may occur with the application of otherwise sublethal doses of miticide when tau-fluvalinate and coumaphos are simultaneously present in the hive."
    • Translocation of neonicotinoid insecticides from coated seeds to seedling guttation drops: A novel way of intoxication for bees
      • This 2009 study, published in the Journal of Economic Entomology, examines "The death of honey bees, Apis mellifera L., and the consequent colony collapse disorder causes major losses in agriculture and plant pollination worldwide. The phenomenon showed increasing rates in the past years, although its causes are still awaiting a clear answer. Here, we show that leaf guttation drops of all the corn plants germinated from neonicotinoid-coated seeds contained amounts of insecticide constantly higher than 10 mg/l, with maxima up to 100 mg/l for thiamethoxam and clothianidin, and up to 200 mg/l for imidacloprid. The concentration of neonicotinoids in guttation drops can be near those of active ingredients commonly applied in field sprays for pest control, or even higher. When bees consume guttation drops, collected from plants grown from neonicotinoid-coated seeds, they encounter death within few minutes."
    • Abnormal foraging behavior induced by sublethal dosage of imidacloprid in the honey bee (Hymenoptera: Apidae)
      • This 2008 study, published in the Journal of Economic Entomology, demonstrates that low dosages of the neonicotinoid insecticide imidacloprid may affect honey bee, Apis mellifera L., behavior. "In this article, the foraging behavior of the honey bee workers was investigated to show the effects of imidacloprid. Results demonstrated that sublethal dosages of imidacloprid were able to affect foraging behavior of honey bees. By measuring the time interval between two visits at the same feeding site, we found that the normal foraging interval of honey bee workers was within 300 s. However, these honey bee workers delayed their return visit for >300 s when they were treated orally with sugar water containing imidacloprid."
    • The relevance of sublethal effects in honey bee testing for pesticide risk assessment
      • This 2007 study, published in Pest Management Science, considers whether and if sublethal effects should be incorporated into risk assessment, by addressing a number of questions: The authors conclude that sublethal studies may be helpful as an optional test to address particular, compound-specific concerns, as a lower-tier alternative to semi-field or field testing, if the effects are shown to be ecologically relevant. However, available higher-tier data (semi-field, field tests) should make any additional sublethal testing unnecessary, and higher-tier data should always override data of lower-tier trials on sublethal effects.
    • Comparative sublethal toxicity of nine pesticides on olfactory learning performances of the honeybee Apis mellifera
      • This 2005 study, published in Archives of Environmental Contamination and Toxicology, used "a conditioned proboscis extension response (PER) assay, honeybees (Apis mellifera L.) can be trained to associate an odor stimulus with a sucrose reward. In the present study, the effects of sublethal concentrations of nine pesticides on learning performances of worker bees subjected to the PER assay were estimated and compared. Reduced learning performances were observed for bees surviving treatment with fipronil, deltamethrin, endosulfan, and prochloraz. A lack of behavioral effects after treatment with lambda-cyalothrin, cypermethrin, tau-fluvalinate, triazamate, and dimethoate was recorded."

    Pesticide impacts on other pollinators

    • Insecticide Use in Hybrid Onion Seed Production Affects Pre- and Postpollination Processes
      • In this 2014 study, published in the Journal of Economic Entomology, researchers conducted a field experiment manipulating insecticide use to examine the impacts of insecticides on 1) pollinator attraction, 2) pollen/stigma interactions, and 3) seed set and seed quality. Select insecticides had negative impacts on pollinator attraction and pollen/stigma interactions, with certain products dramatically reducing pollen germination and pollen tube growth. Decreased pollen germination was not associated with reduced seed set; however, reduced pollinator attraction was associated with lower seed set and seed quality, for one of the two female lines examined. These results highlight the importance of pesticide effects on the pollination process. Overuse may lead to yield reductions through impacts on pollinator behavior and postpollination processes. Overall, in hybrid onion seed production, moderation in insecticide use is advised when controlling onion thrips, Thrips tabaci, on commercial fields.
    • Sublethal neonicotinoid insecticide exposure reduces solitary bee reproductive success
      • This 2013 study published in Agricultural and Forest Entomology “investigated the influence of field-realistic trace residues of the routinely used neonicotinoid insecticides thiamethoxam and clothianidin in nectar substitutes on the entire life-time fitness performance of the red mason bee Osmia bicornis. We show that chronic, dietary neonicotinoid exposure has severe detrimental effects on solitary bee reproductive output. Neonicotinoids did not affect adult bee mortality; however, monitoring of fully controlled experimental populations revealed that sublethal exposure resulted in almost 50% reduced total offspring production and a significantly male-biased offspring sex ratio.
    • Single pollinator species losses reduce floral fidelity and plant reproductive function
      • This 2013 study, published in PNAS, "temporarily removed single pollinator species from study plots in subalpine meadows, to test the hypothesis that interactions between pollinator species can shape individual species’ functional roles via changes in foraging specialization. We show that loss of a single pollinator species reduces floral fidelity (short-term specialization) in the remaining pollinators, with significant implications for ecosystem functioning in terms of reduced plant reproduction, even when potentially effective pollinators remained in the system. Our results suggest that ongoing pollinator declines may have more serious negative implications for plant communities than is currently assumed. More broadly, we show that the individual functional contributions of species can be dynamic and shaped by the community of interspecific competitors, thereby documenting a distinct mechanism for how biodiversity can drive ecosystem functioning, with potential relevance to a wide range of taxa and systems."

    Pesticide impacts on other beneficial organisms

    • Insecticide imidacloprid influences cognitive functions and alters learning performance and related gene expression in a rat model
      • In this 2015 study, published in the International Journal of Experimental Pathology, the effects of different doses of imidacloprid on learning and memory of infant and adult rats were evaluated, and the expressions of genes synthesizing proteins known to be associated with learning in brain tissues were also documented. 0.5, 2 and 8 mg/kg doses of imidacloprid were administered to newborn infant and adult Wistar albino rats by gavage. Their learning activities were evaluated, and the expression levels of the inotropic glutamate receptor GRIN1, synoptophysin, growth-associated protein 43 and the muscarinic receptor M1 in hippocampus were determined by real-time PCR method. Learning activities were diminished significantly at 2 and 8 mg/kg doses in the infant model groups and at 8 mg/kg dose in adult rats. Also, expression levels of GRIN1, SYP and GAP-43 were found to be insignificantly altered. Only the expression of M1 were significantly changed in high doses of adult group. Thus imidacloprid in high doses causes deterioration in cognitive functions particularly in infant rats, and this deterioration may be associated with changes in the expressions of related genes.
    • Insecticide Toxicity to Adelphocoris lineolatus (Hemiptera: Miridae) and Its Nymphal Parasitoid Peristenus spretus(Hymenoptera: Braconidae)
      • In China, Adelphocoris lineolatus (Goeze) (Hemiptera: Miridae) is an important pest of alfalfa, cotton, and other crops, while Peristenus spretus (Chen & van Achterberg) (Hymenoptera: Braconidae) is the dominant nymphal parasitoid of this mirid bug. In this study, published in the Journal of Economic Entomology, the toxicity of 17 common insecticides to A. lineolatus was evaluated, and the susceptibility of P. spretus to the insecticides with high toxicity to A. lineolatus was tested under laboratory conditions. Of the 17 insecticides tested, 12 (beta cypermethrin, deltamethrin, carbosulfan, acetamiprid, emamectin benzoate, imidacloprid, phoxim, chlorpyrifos, acephate, profenophos, hexaflumuron, and abamectin) had a highly toxic effect on second-instar nymphs of A. lineolatus, with LC50 values ranging from 0.58 to 14.85 mg a.i. (active ingredient) liter-1. Adults of P. spretus were most sensitive to chlorpyrifos, with LC50 values of 0.03 mg a.i. liter-1, followed by phoxim, acetamiprid, profenophos, carbosulfan, acephate, deltamethrin, emamectin benzoate, imidacloprid, beta-cypermethrin, and abamectin, with LC50 values ranging from 0.06 to 3.09, whereas hexaflumuron exhibited the least toxicity to the parasitoid, with LC50 values >500 mg a.i. liter-1. A risk quotient analysis indicated that beta-cypermethrin, emamectin benzoate, abamectin, and hexaflumuron when applied against A. lineolatus were the least toxic to P. spretus.
    • Declines in insectivorous birds are associated with high neonicotinoid concentrations
      • In this study, published in Nature, investigated the hypothesis that the most widely used neonicotinoid insecticide, imidacloprid, has a negative impact on insectivorous bird populations. Here researchers show that, in the Netherlands, local population trends were significantly more negative in areas with higher surface-water concentrations of imidacloprid. At imidacloprid concentrations of more than 20 nanograms per litre, bird populations tended to decline by 3.5 per cent on average annually. Additional analyses revealed that this spatial pattern of decline appeared only after the introduction of imidacloprid to the Netherlands, in the mid-1990s. Researchers further show that the recent negative relationship remains after correcting for spatial differences in land-use changes that are known to affect bird populations in farmland. The results suggest that the impact of neonicotinoids on the natural environment is even more substantial than has recently been reported and is reminiscent of the effects of persistent insecticides in the past. Future legislation should take into account the potential cascading effects of neonicotinoids on ecosystems.
    • Risks of large-scale use of systemic insecticides to ecosystem functioning and services
      • In this 2015 review, published in Environmental Science and Research, researchers look over the state of knowledge regarding the potential impacts of these insecticides on ecosystem functioning and services provided by terrestrial and aquatic ecosystems including soil and freshwater functions, fisheries, biological pest control, and pollination services. While empirical studies examining the specific impacts of neonicotinoids and fipronil to ecosystem services have focused largely on the negative impacts to beneficial insect species (honeybees) and the impact on pollination service of food crops, these researchers document broader evidence of the effects on ecosystem functions regulating soil and water quality, pest control, pollination, ecosystem resilience, and community diversity. In particular, microbes, invertebrates, and fish play critical roles as decomposers, pollinators, consumers, and predators, which collectively maintain healthy communities and ecosystem integrity. Several examples in this review demonstrate evidence of the negative impacts of systemic insecticides on decomposition, nutrient cycling, soil respiration, and invertebrate populations valued by humans. Invertebrates, particularly earthworms that are important for soil processes, wild and domestic insect pollinators which are important for plant and crop production, and several freshwater taxa which are involved in aquatic nutrient cycling, were all found to be highly susceptible to lethal and sublethal effects of neonicotinoids and/or fipronil at environmentally relevant concentrations. By contrast, most microbes and fish do not appear to be as sensitive under normal exposure scenarios, though the effects on fish may be important in certain realms such as combined fish-rice farming systems and through food chain effects. The researchers highlight the economic and cultural concerns around agriculture and aquaculture production and the role these insecticides may have in threatening food security. Overall, they recommend improved sustainable agricultural practices that restrict systemic insecticide use to maintain and support several ecosystem services that humans fundamentally depend on.
    • Neonicotinoid contamination of global surface waters and associated risk to aquatic invertebrates: A review
      • In this 2015 review, published in Environmental International, scientists synthesized the current state of knowledge on the reported concentrations of neonicotinoids in surface waters from 29 studies in 9 countries world-wide in tandem with published data on their acute and chronic toxicity to 49 species of aquatic insects and crustaceans spanning 12 invertebrate orders. Strong evidence exists that water-borne neonicotinoid exposures are frequent, long-term and at levels which commonly exceed several existing water quality guidelines. Imidacloprid is by far the most widely studied neonicotinoid (66% of the 214 toxicity tests reviewed) with differences in sensitivity among aquatic invertebrate species ranging several orders of magnitude; other neonicotinoids display analogous modes of action and similar toxicities, although comparative data are limited. Overall, neonicotinoids can exert adverse effects on survival, growth, emergence, mobility, and behavior of many sensitive aquatic invertebrate taxa at concentrations at or below 1μg/L under acute exposure and 0.1μg/L for chronic exposure. Using probabilistic approaches (species sensitivity distributions), researchers recommend here that ecological thresholds for neonicotinoid water concentrations need to be below 0.2μg/L (short-term acute) or 0.035μg/L (long-term chronic) to avoid lasting effects on aquatic invertebrate communities. The application of safety factors may still be warranted considering potential issues of slow recovery, additive or synergistic effects and multiple stressors that can occur in the field. Our analysis revealed that 81% (22/27) and 74% (14/19) of global surface water studies reporting maximum and average individual neonicotinoid concentrations respectively, exceeded these thresholds of 0.2 and 0.035μg/L. Therefore, it appears that environmentally relevant concentrations of neonicotinoids in surface waters worldwide are well within the range where both short- and long-term impacts on aquatic invertebrate species are possible over broad spatial scales.
    • Pyrethroid pesticide effects on behavioral responses of aquatic isopods to danger cues
      • The 2014 study, published in Environmental Science and Pollution Research, sought to evaluate the behavioral responses of non-target organisms in order to determine whether phototactic responses of isopods to danger cues are altered as a function of exposure to the pyrethroid pesticides λ-cyhalothrin and bifenthrin. Experiments conducted on Gnorimosphaeroma oregonensisidentified sublethal behavioral responses to pyrethroids, λ-cyhalothrin and bifenthrin. Experimental setup tested isopod phototactic responses across six treatments: control, pyrethroid, hemolymph, predator, hemolymph + pyrethroid, and predator + pyrethroid. Isopods exhibited no preference for phototactic responses in the control and pyrethroid treatments. When exposed to danger cues (hemolymph or predator), isopods exhibited significant negative phototaxis, as expected. When exposure to danger cues was combined with pyrethroids, isopods again exhibited no preference for phototactic response. Experiments indicate that pyrethroids diminish isopod’s negatively phototactic response to danger cues.
    • Impacts of a neonicotinoid, neonicotinoid–pyrethroid premix, and anthranilic diamide insecticide on four species of turf-inhabiting beneficial insects
      • In this 2014 study, published in Ecotoxicology, researchers compared the impact of a neonicotinoid (clothianidin), a premix (clothianidin + bifenthrin), and an anthranilic diamide (chlorantraniliprole), the main insecticide classes used for multiple targeting, on four species of beneficial insects: Harpalus pennsylvanicus, an omnivorous ground beetle, Tiphia vernalis, an ectoparasitoid of scarab grubs, Copidosoma bakeri, a polyembryonic endoparasitoid of black cutworms, and Bombus impatiens, a native bumble bee. Ground beetles that ingested food treated with clothianidin or the premix suffered high mortality, as did C. bakeri wasps exposed to dry residues of those insecticides. Exposure to those insecticides on potted turf cores reduced parasitism by T. vernalis. Bumble bee colonies confined to forage on white clover (Trifolium repens L.) in weedy turf that had been treated with clothianidin or the premix had reduced numbers of workers, honey pots, and immature bees. Premix residues incapacitated H. pennsylvanicus and C. bakeri slightly faster than clothianidin alone, but otherwise we detected no synergistic or additive effects. Chlorantraniliprole had no apparent adverse effects on any of the beneficial species. Implications for controlling turf pests with least disruption of non-target invertebrates are discussed.
    • Lethal and behavioral effects of pesticides on the insect predator Macrolophus pygmaeus
      • The 2014 study published in Chemosphere examines the lethal and sublethal effects of six insecticides and a fungicide on the beneficial insect Macrolophus pygmaeus. They found “Thiacloprid and metaflumizone caused 100% and 80% mortality, respectively, and were classified as harmful. Indoxacarb and spinosad resulted in close to 30% mortality to the predator, and were classified as slightly harmful, while the fungicide copper hydroxide caused 58% mortality and was rated as moderately harmful. Chlorantraniliprole and thiacloprid were selected for further sublethal testing by exposing M. pygmaeus to two routes of pesticide intake: pesticide residues and feeding on sprayed food. Thiacloprid led to an increase in resting and preening time of the predator, and a decrease in plant feeding. Chlorantraniliprole resulted in a decrease in plant feeding, but no other behaviors were affected.”
    • Impacts of orchard pesticides on Galendromus occidentalis: Lethal and sublethal effects
      • This 2014 study published in Crop Protection tests the lethal and sublethal effects of fifteen pesticides on the principal mite predator in Washington apple orchards.Their studies provide support for the impact of sublethal effects of “reduced-risk pesticides” on beneficial species. “At the 1_ dose, only spinetoram and lambda-cyhalothrin caused >75% acute mortality of females. Carbaryl, azinphos methyl, spinosad, spirotetramat, cyantraniliprole, and sulfur had relatively little effect on mortality, but moderate to high effects on fecundity. Egg viability was most affected by carbaryl, spinosad, novaluron, spirotetramat, and sulfur. Lambda-cyhalothrin, spinosad, and sulfur were the most toxic compounds to larvae. Materials such as sulfur and spinetoram had widely divergent toxicity to adults versus larvae. The cumulative impact of these effects was best integrated by the numbers of live larvae of the F1 generation. Using this measurement, spirotetramat, sulfur, spinetoram, acetamiprid, lambda-cyhalothrin, carbaryl and novaluron caused the greatest percentage reduction compared to the check, yet only spinetoram and lambda-cyhalothrin would have been identified as harmful in acute bioassays.”
    • The impact of insecticides applied in apple orchards on the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae)
      • This 2013 study, published in Experimental and Applied Acarology, examines the side effects of insecticides on a predatory mite in apple orchards, finding that they did not in fact diminish their populations as intended. “Spider mite (Panonychus ulmi) populations reached higher densities on plots treated with etofenprox and tau-fluvalinate than in the other treatments. Single or multiple applications of neonicotinoids caused no detrimental effects on predatory mites. In the laboratory, spinosad and tau-fluvalinate caused 100 % mortality. Etofenprox caused a significant mortality and reduced fecundity. The remaining insecticides did not affect female survival except for imidacloprid. Thiamethoxam, clothianidin, thiacloprid, chlorpyrifos, lufenuron and methoxyfenozide were associated with a significant reduction in fecundity. No effect on fecundity was found for indoxacarb or acetamiprid. Escape rate of K. aberrans in laboratory was relatively high for etofenprox and spinosad, and to a lesser extent thiacloprid. The use of etofenprox, tau-fluvalinate and spinosad was detrimental for K. aberrans and the first two insecticides induced spider mite population increases. The remaining insecticides caused no negative effects on predatory mites in field trials.”
    • Imidacloprid affects the functional response of predator Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) to strains ofSpodoptera frugiperda (J.E. Smith) on Bt cotto
      • This 2013 study published in Ecotoxicology examines the impact of imidacloprid on an important biological control agent for many crops in South and Central America. The species, Podisus nigrispinus feeds on several pests including Spodoptera frugiperda.Researchers found that although the pest S. frugiperda became more aggressive, the beneficial insect P. nigrispinus showed significantly lower predation rates when exposed to imidacloprid.
    • Effect of imidacloprid on the biochemical contents of kidneys in male Swiss albino mice
      • This 2013 study published in The Bioscan examines mice that were orally administered varied doses of imidacloprid to determine their effects.” Kidney is the target organ for a wide variety of toxic agents as it acts as a blood filter during the excretory process. As kidneys receive high blood flow, the insecticides might be delivered to these organs in relatively high amounts through systemic (blood) circulation.” The study found that “The present findings on the toxicity of imidacloprid in mice suggest significant decrease in the level of protein, DNA and RNA in kidneys. Though six groups of the experimental mice were treated with varied concentrations of imidacloprid, the decrease of protein, DNA and RNA was not dose dependent in any of the 3 test organs”
    • Detection and analysis of neonicotinoids in river waters – Development of a passive sampler for three commonly used insecticides
      • This 2013 study published in Chemosphere examined a new method to detect and analyze five of the most common neonicotinoid compounds in rivers around Sydney, Australia, where 93% of samples contained two or more neonicotinoids. “As a consequence of their high water solubility and persistence in soil they pose a risk of water contamination, particularly after storm events that produce runoff pulses and by leaching to the groundwater.”
    • Trace level determination of pyrethroid and neonicotinoid insecticides in beebread using acetonitrile-based extraction followed by analysis with ultra-high-performance liquid chromatography–tandem mass spectrometry
      • This 2013 study published in the Journal of Chromatography A analysis of 32 samples of beebread from various regions in France to discover contamination levels of pyrethroids and neonicotinoids. The study detected 14 target pesticides and metabolites at sublethal levels, while 7 target substances were detected in beebread samples collected from hives. The study found that “The most frequently detected pesticides belonged to the neonicotinoid family and were generally present at low concentrations, but in some cases exceeded 170ng/g (acetamiprid and thiacloprid). Some pyrethroids were also detected (lambda-cyhalothrine and bifenthrine), but at very low levels.”
    • Pesticides reduce regional biodiversity of stream invertebrates
      • This 2013 study, published in Proceedings of the National Academy of Sciences "analyzed the effects of pesticides on the regional taxa richness of stream invertebrates in Europe (Germany and France) and Australia (southern Victoria). Pesticides caused statistically significant effects on both the species and family richness in both regions, with losses in taxa up to 42% of the recorded taxonomic pools. Furthermore, the effects in Europe were detected at concentrations that current legislation considers environmentally protective. Thus, the current ecological risk assessment of pesticides falls short of protecting biodiversity, and new approaches linking ecology and ecotoxicology are needed."
    • An overview of the environmental risks posed by neonicotinoid insecticides
      • This 2013 study, published in the Journal of Applied Ecology, determines that neonicotinoid pesticides have broad ranging negative impacts not only on beneficial pollinators, but on overall biodiversity and ecosystem health. "They are water soluble and prone to leaching into waterways. Being systemic, they are found in nectar and pollen of treated crops. Reported levels in soils, waterways, field margin plants and floral resources overlap substantially with concentrations that are sufficient to control pests in crops, and commonly exceed the LC50 (the concentration which kills 50% of individuals) for beneficial organisms. Concentrations in nectar and pollen in crops are sufficient to impact substantially on colony reproduction in bumblebees. Although vertebrates are less susceptible than arthropods, consumption of small numbers of dressed seeds offers a route to direct mortality in birds and mammals... Major knowledge gaps remain, but current use of neonicotinoids is likely to be impacting on a broad range of non-target taxa including pollinators and soil and aquatic invertebrates and hence threatens a range of ecosystem services."
    • Wildlife ecotoxicology of pesticides: can we track effects to the population level and beyond?
      • This 2013 study published in Science, examines the role of pesticides, including bee-killing pesticides, on wildlife. "One of the major challenges in wildlife ecotoxicology... is to trace the effects and side effects of chemicals, from their cellular targets through levels of increasing complexity to communities of species and the function of ecosystems. Here we provide an integrated view of the existing knowledge regarding pesticides of the past and present. This includes synthetic chemicals and biological compounds applied in agriculture..."
    • Reproductive Effects of Two Neonicotinoid Insecticides on Mouse Sperm Function and Early Embryonic Development In Vitro
      • This 2013 study, published in the journal PLoS ONE examined the role of two neonicotinoids, Acetamiprid and imidacloprid on reproduction " by using an integrated testing strategy for reproductive toxicology, which covered sperm quality, sperm penetration into oocytes and preimplantation embryonic development. Direct chemical exposure (500 mM or 5 mM) on spermatozoa during capacitation was performed, and in vitro fertilization (IVF) process, zygotes and 2-cell embryos were respectively incubated with chemical-supplemented medium until blastocyst formation to evaluate the reproductive toxicity of these chemicals and monitor the stages mainly affected. Generally, treatment of 500 mM or 5 mM chemicals for 30 min did not change sperm motility and DNA integrity significantly but the fertilization ability in in vitro fertilization (IVF) process, indicating that IVF process could detect and distinguish subtle effect of spermatozoa exposed to different chemicals. Culture experiment in the presence of chemicals in medium showed that fertilization process and zygotes are adversely affected by direct exposure of chemicals (P,0.05), in an order of nicotine.IMI.ACE, whereas developmental progression of 2-cell stage embryos was similar to controls (P.0.05). These findings unveiled the hazardous
        effects of neonicotinoid pesticides exposure on mammalian sperm fertilization ability as well as embryonic development,
        raising the concerns that neonicotinoid pesticides may pose reproductive risks on human reproductive health, especially in
        professional populations.
    • Immunotoxic effects of imidacloprid following 28 days of oral exposure in BALB/c mice
      • This 2013 study, published in Environmental Toxicology and Pharmacology, evaluated "immunotoxic effects of imidacloprid in female BALB/c mice. Imidacloprid was administered orally daily at 10, 5, or 2.5 mg/kg over 28 days. Specific parameters of humoral and cellular immune response including hemagglutinating antibody (HA) titer to sheep red blood cells (SRBC; T-dependent antigen), delayed type hypersensitivity (DTH) response to SRBC, and T-lymphocyte proliferation in response to phytohemagglutinin (PHA) were evaluated. The results showed that imidacloprid at high dose, specifically suppressed cell-mediated immune response as was evident from decreased DTH response and decreased stimulation index of T-lymphocytes to PHA. At this dose, there were also prominent histopathological alterations in spleen and liver. Histopathological analysis of footpad sections of mice revealed dose-related suppression of DTH response. Imidacloprid at low dose of 2.5 mg/kg/day did not produce any significant alterations in cellular and humoral immune response and it seemed to be an appropriate dose for assessment of ‘no observable adverse effects level’ for immunotoxicity in BALB/c mice. The results also indicated that imidacloprid has immunosuppressive effects at doses >5 mg/kg, which could potentially be attributed to direct cytotoxic effects of IMD against T cells (particularly TH cells) and that long-term exposure could be detrimental to the immune system."
    • Assessment of imidacloprid toxicity on reproductive organ system of adult male rats
      • This 2012 study, published in the Journal of Environmental Science and Health, investigated "the toxicity of low doses of imidacloprid (IMI) on the reproductive organ systems of adult male rats. The treatment groups received 0.5 (IMI-0.5), 2 (IMI-2) or 8 mg IMI/kg body weight by oral gavage (IMI-8) for three months. The deterioration in sperm motility in IMI-8 group and epidydimal sperm concentration in IMI-2 and IMI-8 groups and abnormality in sperm morphology in IMI-8 were significant. The levels of testosterone (T) and GSH decreased significantly in group IMI-8 compared to the control group. Upon treatment with IMI, apoptotic index increased significantly only in germ cells of the seminiferous tubules of IMI-8 group when compared to control. Fragmentation was striking in the seminal DNA from the IMI-8 group, but it was much less obvious in the IMI-2 one. IMI exposure resulted in elevation of all fatty acids analyzed,
        but the increases were significant only in stearic, oleic, linoleic and arachidonic acids. The ratios of 20:4/20:3 and 20:4/18:2 were
        decreased and 16:1n-9/16:0 ratio was increased. In conclusion, the present animal experiments revealed that the treatment with IMI
        at NOAEL dose-levels caused deterioration in sperm parameters, decreased T level, increased apoptosis of germ cells, seminal DNA fragmentation, the depletion of antioxidants and change in disturbance of fatty acid composition. All these changes indicate the
        suppression of testicular function."
    • Chronic exposure to imidacloprid induces inflammation and oxidative stress in the liver & central nervous system of rats
      • This 2012 study, published in Pesticide Chemistry and Physiology, examined "oxidant and inflammatory responses to chronic exposure of imidacloprid... in rats. Wistar rats were randomly allocated into two groups as control and imidacloprid-exposed group (n = 10 rat/each group).1 mg/kg/BW/day imidacloprid was administrated orally by gavage for 30 days. After exposure, rats were euthanized and liver and brain samples were surgically removed for analyses. Imidacloprid application caused a significant increase in nitric oxide production in brain (p < 0.05) and liver (p < 0.001). The quantitative analyses of mRNA confirmed the finding that imidacloprid induced the mRNA transcriptions of the three isoforms of nitric oxide synthases (iNOS, eNOS, nNOS) in brain and two isoforms (iNOS, eNOS) in the liver. Exposure to imidacloprid caused significant lipid peroxidation in plasma, brain (p < 0.001) and liver (p < 0.003). While the superoxide-generating enzyme xanthine oxidase activity was elevated in both tissues (p < 0.001), myeloperoxidase activity was increased only in the liver (p < 0.001). Antioxidant enzyme activities showed various alterations following exposure, but a significantly depleted antioxidant glutathione level was detected in brain (p < 0.008). Evidence of chronic inflammation by imidacloprid was observed as induction of pro-inflammatory cytokines such as TNF-a, IL-1b, IL-6, IL- 12 and IFN-c in the liver and brain. In conclusion, chronic imidacloprid exposure causes oxidative stress and inflammation by altering antioxidant systems and inducing pro-inflammatory cytokine production in the liver and central nervous system of non-target organisms.
    • The molecular basis of simple relationships between exposure concentration and toxic effects with time
      • This 2013 review, published in Toxicology, " re-introduces an old approach that takes into account the biochemical mode of action and their resulting biological effects over time of exposure. Empirical evidence demonstrates that the Druckrey–Küpfmüller toxicity model, which was validated for chemical carcinogens in the early 1960s, is also applicable to a wide range of toxic compounds in ecotoxicology. According to this model, the character of a poison is primarily determined by the reversibility of critical receptor binding. Chemicals showing irreversible or slowly reversible binding to specific receptors will produce cumulative effects with time of exposure, and whenever the effects are also irreversible (e.g. death) they are reinforced over time; these chemicals have time-cumulative toxicity. Compounds having non-specific receptor binding, or involving slowly reversible binding to some receptors that do not contribute to toxicity, may also be time-dependent; however, their effects depend primarily on the exposure concentration, with time playing a minor role. Consequently, the mechanism of toxic action has important implications for risk assessment. Traditional risk approaches cannot predict the impacts of toxicants with time-cumulative toxicity in the environment. New assessment procedures are needed to evaluate the risk that the latter chemicals pose on humans and the environment."
    • Water polluted with imidacloprid linked to low numbers of aquatic insects
      • This 2013 study, published in the journal PLoS ONE, found 70% fewer invertebrate species in water polluted with imidacloprid compared to clean water in the Netherlands. Mayflies, midges and molluscs, were all severely impacted with potential harm to their predators like birds. Researchers compiled and analyzed information from 700 sites between 1998 and 2009 to determine the impacts of water quality on wildlife. For highly polluted waters that exceeded the Dutch pollution limits, only 17 species were found on average in comparison to 52 species in clean water.
    • Effects of aldicarb and neonicotinoid seed treatments on twospotted spider mite on cotton 
      • This 2013 study, published in the Journal of Economic Entomology, indicates that neonicotinoid seed treatments increase infestation of pest species in cotton crops. "Twelve field experiments and one laboratory experiment were conducted to determine the effects of furrow applied aldicarb and seed treatments of thiamethoxam, imidacloprid, Avicta (thiamethoxam + abamectin), Aeris (imidacloprid + thiodicarb), and acephate on twospotted spider mite, Tetranychus urticae Koch, on cotton, Gossypium hirsutum L. For the field experiments, data were pooled across all experiments for analysis.eris, thiamethoxam, and imidacloprid treatments resulted in twospotted spider mite densities greater than those in the untreated check, aldicarb, and acephate treatments. However, cotton treated with Avicta (thiamethoxam + abameetin) had 34% fewer mites than other neonicotinoid seed treatments when infestations occurred near cotyledon stage. Untreated check and aldicarb treatments had the lowest mite densities. Only aldicarb reduced mite densities below that in the untreated check. In a laboratory trial, the fecundity of twospotted spider mite was measured. While neonicotinoid seed treatments increased mite densities in the field, they did not increase fecundity in the laboratory experiment."
    • Lethal and sublethal effects of imidacloprid and buprofezin on the sweetpotato whitefly parasitoid
      • This 2013 study, published in Crop Protection, demonstrated that the longevity and fecundity of the parasitoid, E.mundus, were reduced significantly by the two insecticides, though the sex ratio of E.mundus offspring was not affected. Population parameters of the parasitoid such as R0rm and T were also significantly reduced by the insecticides. Our results indicated that, in addition to lethal effects, sublethal effects should also be considered when these insecticides are applied.
    • Environmental impact of imidacloprid on soil fertility: a case study on Drawida willsi earthworm 
      • This 2013 study published in The Clarion, focused on imidacloprid, one of the major components of many widely used insecticides and is relatively persistent in soils. Earthworms are used as indicator species for ecotoxicological evaluation and risk assessment. The effect of Imidacloprid on mortality of a dominant crop field earthworm (Drawida willsi, Michaelsen) was studied under ideal laboratory conditions to rice field soil. The concluded that although the doses were sometimes low, that imidacloprid could affect the soil biota by altering its vita rates and metabolism.
    • Studies on the electrolytes and microelements in Wistar rat following multiple exposures to acetamiprid
      • This 2012 study, published in Toxicology and Industrial Health, performed a "subacute toxicity study of acetamiprid... in 72 female Wistar rats randomly divided into four groups (18 each). Acetamiprid was administered orally at the dose rate of 0, 25, 100 and 200 mg/kg of body weight to rats of groups I, II, III and IV, respectively. Group I served as control. Calcium, phosphorous, sodium, potassium, chloride, zinc, copper, iron and cobalt concentrations in plasma were significantly (p  0.05) increased in acetamiprid administered groups. However, no alteration was observed in plasma manganese concentration in acetamiprid-treated rats. The repeated oral toxicity study on acetamiprid in present investigation suggested that it has toxic potential and it is a high-risk insecticide."
    • Effects of binary mixtures on the life traits of Daphnia magna
      • This 2011 study, published in Ecotoxicology and Environmental Safety, assesses "the joint effect of chemical mixtures to the life—history traits of Daphnia magna Straus. For that a binary mixture of two neonicotinoid insecticides, imidacloprid and thiacloprid, and another one of imidacloprid with nickel chloride were tested. Theoretical models have been developed and applied in studies with chemical mixtures, predicting toxicity based on their modes of action: concentration addition (CA) and independent joint action (IA) models. Still there are cases where deviations are observed (e.g. synergistic or antagonistic behaviors, dose ratio or level dependency). In this study, the effects of the individual compounds and their mixtures were studied in a chronic test where reproduction, survival and body length were evaluated in D. magna. Regarding single compound effects, it was observed that the most toxic was nickel chloride followed by thiacloprid and imidacloprid. For the mixture exposure of imidacloprid and thiacloprid, a synergistic pattern was observed in the sublethal doses used for the number of neonates produced, while for the body length the best fit was shown with the CA model. In the mixture exposure of imidacloprid and nickel, no deviation from the IA was observed for the neonate production data; for the body length parameter, a synergistic pattern was observed in low doses of the chemicals while an antagonistic pattern was observed."
    • Pesticide exposure and inducible antipredator responses in the zooplankton grazer, Daphnia magna Straus
      • This 2010 study, published in Chemosphere, studies "the effects of the pesticide imidacloprid on the responses of Daphnia magnato a combination of predator-release kairomones from trout and alarm cues from conspecifics, simulating different levels of perceived predation risk. The joint effects of simultaneous exposure to both types of stressors were assessed both by traditional analysis of variance and by employing conceptual models for the evaluation of contaminant mixture exposures. Results demonstrated that pesticide exposure can significantly increase the costs of inducible antipredator defences and impair life-history responses of daphnids to fish predation pressure. Since trait-mediated effects are well-known to play a key role in population dynamics, the combined direct and indirect effects of sub-lethal concentrations of pesticides could induce maladaptive responses in zooplankton populations in the field, reducing their long-term viability."
    • The significance of the Druckrey-Küpfmüller equation for risk assessment - The toxicity of neonicotinoid insecticides to arthropods is reinforced by exposure time 
      • This 2010 study, published in Toxicology, examines The Druckrey-Küpfmüller equation which "explains why toxicity may occur after prolonged exposure to very low toxicant levels. Recently, similar dose-response characteristics have been established for the toxicity of the neonicotinoid insecticides imidacloprid and thiacloprid to arthropods. This observation is highly relevant for environmental risk assessment. Traditional approaches that consider toxic effects at fixed exposure times are unable to allow extrapolation from measured endpoints to effects that may occur at other times of exposure. Time-to-effect approaches that provide information on the doses and exposure times needed to produce toxic effects on tested organisms are required for prediction of toxic effects for any combination of concentration and time in the environment." See: Daily News Blog.
    • Assessing the effects of the neonicotinoid insecticide imidacloprid in the cholinergic synapses of the stellate cells of the mouse cochlear nucleus using whole-cell patch-clamp recording
      • This 2010 study, published in Neurotoxicology, sought to "determine to what extent imidacloprid (IMI) affects the nAChRs of the stellate cells of mouse cochlear nucleus (CN), using whole-cell patch-clamp recording. Puff application of 1 mM IMI had no significant effect on the membrane properties of the neurons tested, while a concentration of 10 mM caused a significant depolarizing shift in themembrane potential and resulted in increases in the fluctuation of the membrane potential and in the frequency of miniature postsynaptic potentials (mpps) within less than a minute of exposure. IMI at concentrations 50 mMcaused a significant depolarizing shift in themembrane potential, accompanied by amarked increase in the frequency of action potential. IMI decreased the membrane input resistance and the membrane time constants. Bath application of 50 mM d-tubocurarine (d-TC) reversibly blocked the depolarizing shift of the resting membrane potential and the spontaneous firing induced by IMI application in current clamp and blocked the inward currents through nicotinic receptors induced by IMI application in voltage clamp. Similarly, 100 nMa-bungarotoxin (a-BgTx) blocked the spontaneous firing induced by IMI (n = 3). The amplitude of the 100 mM IMI-induced inward current at 60 mV holding potential was 115.0  16.2 pA (n = 7). IMI at a concentration of 10 mM produced 11.3  3.4 pA inward current (n = 4). We conclude that exposure to IMI at concentrations 10 mM for <1 min can change the membrane properties of neurons that have nAChRs and, as a consequence, their function.
    • Acute oxidant and inflammatory effects of imidacloprid on the mammalian central nervous system and liver in rats
      • In this 2010 study, published in Pesticide Toxicology and Physiology, researchered examined "potential acute neuro and liver toxic effects of imidacloprid... in rats as a model of mammalian using antioxidant–oxidant and inflammatory system. 10 lM imidacloprid was administrated intravenously and 2 h post-administration, the rats were sacrificed, liver and brains were surgically removed. Exposure to imidacloprid led to significant increases in nitric oxide concentrations in brain, liver and plasma samples. The quantitative mRNA transcriptional analyses demonstrated that imidacloprid-elevated production of NO levels due to the induction of iNOS in liver, but neither nNOS nor iNOS were induced in brain. The oxidant-generating enzymes xanthine oxidase and myeloperoxidase activities in both tissues were elevated and significant lipid peroxidation in liver and plasma was observed. The antioxidant catalase, superoxide dismutase and glutathione peroxidase activities were differently responded to imidacloprid administration. Significant intracellular glutathione depletion was also measured in both tissues. Imidacloprid treatment upregulated inflammatory cytokines TNF-a, IL-6 and IL-1b mRNA transcriptions by 2.5- to 5.2-fold increases in both brain and liver. Conversely, anti-inflammatory mediator IL-10 mRNA was down-regulated in both organs. These results suggest that imidacloprid cause oxidative stress and inflammation in central nervous system and liver in non-target organisms in rats."
    • The impact of neonicotinoid insecticides on bumblebees, Honey bees and other non-target invertebrates
      • This 2009 report, published by BugLife,, reviews existing approvals research and independent research on the effects of neonicotinoid pesticides on Honey bees, bumblebees and other non-target invertebrates, and investigates the current approvals mechanism and its standards.

    Parasites and Viruses

    • bee flowerBee declines driven by combined stress from parasites, pesticides, and lack of flowers
      • In this review, published in Science, the authors recognize that bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined, bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple, interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future.
    • Honeybee Colony Disorder in Crop Areas: The Role of Pesticides and Viruses
      • The present study, published in PLOS ONE in 2014, aims to determine the role of both pesticide exposure and virus load on the appraisal of unexplained honeybee colony disorders in field conditions. From July 2011 to May 2012, 330 colonies were monitored. Three acaricides, 5 insecticides and 13 fungicides were detected in the analyzed samples. A significant correlation was found between the presence of fungicide residues and honeybee colony disorders. A significant positive link could also be established between the observation of disorder and the abundance of crop surface around the beehive. According to the results, the researchers state that the role of fungicides as a potential stressor for honeybee colonies should be further studied, either by their direct and/or indirect impacts on bees and bee colonies.
    • Impact of chronic exposure to a pyrethroid pesticide on bumblebees and interactions with a trypanosome parasite
      • In this 2014 study, published in the Journal of Applied Ecology, researchers focus on the impacts of chronic exposure to the commonly used pyrethroid pesticide lambda (λ)-cyhalothrin on the bumblebee Bombus terrestris at both the individual and colony level. Furthermore, they investigated the interactions of pesticide exposure with a highly prevalent trypanosome parasite Crithidia bombi. Pesticide-treated colonies produced workers with a significantly lower body mass. However, out of the twelve variables of colony development measured, this was the only metric that was significantly affected by pesticide treatment and there was no subsequent significant impact on the reproductive output of colonies. Lambda-cyhalothrin had no significant impact on the susceptibility of workers to C. bombi, or intensity of parasitic infection. Pesticide exposure did not cause differential survival in workers or males, even when workers were additionally challenged with C. bombi. Chronic exposure to λ-cyhalothrin has a significant impact on worker size, a key aspect of bumblebee colony function, particularly under conditions of limited food resources. This could indicate that under times of resource limitation, colonies exposed to this pesticide in the field may fail. However, the lack of other impacts found in this study indicates that further field trials are needed to elucidate this.
    • Transcriptome Analyses of the Honeybee Response to Nosema ceranae and Insecticides
      • In this 2014 study, published in PLOS ONE, researchers investigated the molecular response of honeybees exposed to N. ceranae, to insecticides (fipronil or imidacloprid), and to a combination of both stressors. Midgut transcriptional changes induced by these stressors were measured in two independent experiments. Although N. ceranae-insecticide combinations induced a significant increase in honeybee mortality, researchers observed that they did not lead to a synergistic effect. According to gene expression profiles, chronic exposure to insecticides had no significant impact on detoxifying genes but repressed the expression of immunity-related genes. Honeybees treated with N. ceranae, alone or in combination with an insecticide, showed a strong alteration of midgut immunity together with modifications affecting cuticle coatings and trehalose metabolism. An increasing impact of treatments on gene expression profiles with time was identified suggesting an absence of stress recovery which could be linked to the higher mortality rates observed.
    • Evaluation of the Distribution and Impacts of Parasites, Pathogens, and Pesticides on Honey Bee (Apis mellifera) Populations in East Africa
      • In this 2014 study, published in PLOS ONE, researchers initiated a nationwide survey encompassing 24 locations across Kenya in 2010 to evaluate the numbers and sizes of honey bee colonies, assess the presence of parasites (Varroa mites and Nosemamicrosporidia) and viruses, identify and quantify pesticide contaminants in hives, and assay for levels of hygienic behavior. The results suggest that Varroa, the three viruses, and Nosema have been relatively recently introduced into Kenya, but these factors do not yet appear to be impacting Kenyan bee populations. Thus chemical control for Varroa and Nosema are not necessary for Kenyan bees at this time. This study provides baseline data for future analyses of the possible mechanisms underlying resistance to and the long-term impacts of these factors on African bee populations.
    • Thiacloprid–Nosema ceranae interactions in honey bees: Host survivorship but not parasite reproduction is dependent on pesticide dose
      • In this 2014 study, published in the Journal of Invertebrate Pathology, researchers demonstrated that a synergistic effect on mortality by the low toxic, commonly used neonicotinoid thiacloprid and the nearly ubiquitous gut parasite Nosema ceranae is dependent on the pesticide dose. Furthermore, thiacloprid had a negative influence on N. ceranae reproduction. These results highlight that interactions among honey bee health stressors can be dynamic and should be studied across a broader range of combinations.
    • A Causal Analysis of Observed Declines in Managed Honey Bees (Apis mellifera)
      • This 2013 study, published in Human and Ecological Risk Assessment: An International Journal, summarized the results of a workshop that was convened during which bee experts were introduced to a formal causal analysis approach to compare 39 candidate causes against specified criteria to evaluate their relationship to the reduced overwinter survivability observed since 2006 of commercial bees used in the California almond industry. Candidate causes were categorized as probable, possible, or unlikely; several candidate causes were categorized as indeterminate due to lack of information. Due to time limitations, a full causal analysis was not completed at the workshop. In this article, examples are provided to illustrate the process and provide preliminary findings, using three candidate causes. Varroa mites plus viruses were judged to be a “probable cause” of the reduced survival, while nutrient deficiency was judged to be a “possible cause.” Neonicotinoid pesticides were judged to be “unlikely” as the sole cause of this reduced survival, although they could possibly be a contributing factor.
    • Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae
      • This 2013 study published in the journal PLoS ONE importantly evaluated field relevant combinations and loads of pesticides and their effect on honey bee health. “We collected pollen from bee hives in seven major crops to determine 1) what types of pesticides bees are exposed to when rented for pollination of various crops and 2) how field-relevant pesticide blends affect bees’ susceptibility to the gut parasite Nosema ceranae.” The study found that there were 35 different pesticides in the sampled pollen, and found high fungicide loads. “While fungicides are typically seen as fairly safe for honey bees, we found an increased probability of Nosema infection in bees that consumed pollen with a higher fungicide load. Our results highlight a need for research on sub-lethal effects of fungicides and other chemicals that bees placed in an agricultural setting are exposed to.”
    • Towards a systems approach for understanding honeybee decline: a stocktaking and synthesis of existing models
      • This 2013 study published in Journal of Applied Ecology reviewed "existing honeybee models that are relevant to examining the effects of different stressors on colony growth and survival. Most of these models describe honeybee colony dynamics, foraging behaviour or honeybee – varroa mite – virus interactions. We found that many, but not all, processes within honeybee colonies, epidemiology and foraging are well understood and described in the models, but there is no model that couples in-hive dynamics and pathology with foraging dynamics in realistic landscapes."
    • Pesticide exposure in honey bees results in increased levels of the gut pathogen Nosema.
      • Study exposed honey bee colonies during three brood generations to sub-lethal doses of a widely used pesticide, imidacloprid, and then subsequently challenged newly emerged bees with the gut parasite, Nosema spp. The pesticide dosages used were below levels demonstrated to cause effects on longevity or foraging in adult honey bees. Nosema infections increased significantly in the bees from pesticide-treated hives when compared to bees from control hives demonstrating an indirect effect of pesticides on pathogen growth in honey bees. Interactions between pesticides and pathogens could be a major contributor to increased mortality of honey bee colonies, including colony collapse disorder, and other pollinator declines worldwide.
    • A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis. 
      • Study provides the first documentation that the phorid fly Apocephalus borealis, previously known to parasitize bumble bees, also infects and eventually kills honey bees and may pose an emerging threat to North American apiculture. Parasitized honey bees show hive abandonment behavior, leaving their hives at night and dying shortly thereafter. On average, seven days later up to 13 phorid larvae emerge from each dead bee and pupate away from the bee. Using DNA barcoding, study confirmed that phorids that emerged from honey bees and bumble bees were the same species. Phorid parasitism may affect hive viability since 77% of sites sampled in the San Francisco Bay Area were infected by the fly and microarray analyses detected phorids in commercial hives in South Dakota and California's Central Valley. Study concludes that understanding details of phorid infection may shed light on similar hive abandonment behaviors seen in CCD.
    • Iridovirus and Microsporidian Linked to Honey Bee Colony Decline 
      • Synopsis: In 2010 Colony Collapse Disorder (CCD), again devastated honey bee colonies in the USA, indicating that the problem is neither diminishing nor has it been resolved. Many CCD investigations, using sensitive genome-based methods, have found small RNA bee viruses and the microsporidia, Nosema apis and N. ceranae in healthy and collapsing colonies alike with no single pathogen firmly linked to honey bee losses. These findings implicate co-infection by invertebrate iridescent virus (IIV) (Iridoviridae) and Nosema with honey bee colony decline, giving credence to older research pointing to IIV, interacting with Nosema and mites, as probable cause of bee losses in the USA, Europe, and Asia. See: Daily News Blog
    • Nosema ceranae, a newly identified pathogen of Apis mellifera in the U.S. and Asia 
      • Synopsis: Nosemosis (Nosema disease) is one of the most serious and prevalent adult honey bee diseases worldwide. For years, Nosema apis was thought to be the only microsporidia infecting domestic bee colonies. However, recently it was discovered that N. ceranae could jump from Asian honey bees (Apis cerana) to European honey bees (Apis mellifera) that are widely used for crop pollination. The data presented in the studies demonstrated that N. ceranae infection is widespread in the U.S., China and Australia and that infection with N. ceranae was more common than infection with N. apis in European honey bees. The finding about the prevalence of N. ceranae in the U.S. and Asian bee populations in conjunction with findings in other parts of the world invites further research of the evolutionary history of N. ceranae infection in European honey bees.
    • Winter losses of honeybee colonies (Apis mellifera): The role of infestations with Aethina tumida and Varroa destructor 
      • Synopsis: Multiple infections and infestations of honeybee colonies with pathogens and parasites are inevitable due to the ubiquitous ectoparasitic mite Varroa destructor and might be one of the mechanisms underlying winter losses. Here the authors investigated the role of adult small hive beetles, Aethina tumida, alone and in combination with V. destructor for winter losses and infections with the microsporidian endoparasite Nosema ceranae. High losses occurred in all groups highly infested with V. destructor, supporting the central role of this mite in colony losses. Data suggest that A. tumida alone is unlikely to contribute to losses of overwintering honeybee colonies.
    • Changes in Gene Expression Relating to Colony Collapse Disorder in honey bees, Apis mellifera 
      • Synopsis: Colony collapse disorder (CCD) is a mysterious disappearance of honey bees that has beset beekeepers in the United States since late in 2006. Pathogens and other environmental stresses, including pesticides, have been linked to CCD, but a causal relationship has not yet been demonstrated. Considerable variation in gene expression was associated with the geographical origin of bees, but a consensus list of 65 transcripts was identified as potential genetic markers for CCD status. Reduced expression of two genes associated with detoxification and a mixed response from genes involved in immune function were observed. Unusual ribosomal RNA fragments were also conspicuously more abundant in CCD bee guts. The presence of these fragments may be a possible consequence of picornavirus infection. Ribosomal fragment abundance and viral presence may prove useful as diagnostic markers for colonies afflicted with CCD.
    • Honeybee Sacbrood virus infects adult small hive beetles, Aethina tumida (Coleoptera: Nitidulidae) 
      • Synopsis: The Small Hive Beetle (SHB) is a recently discovered pest that invades honey bee colonies and causes damage to comb, stored honey and pollen. A laboratory experiment was conducted to investigate whether SHB could harbor honey bee virus(es) via feeding on virus infected brood and thereby serving as a vector of viruses in honey bee colonies. Study demonstrated for the first time that SHB could become infected with honey bee Sacbrood virus (SBV) via the food-borne transmission route. This study should raise awareness among scientists, beekeepers, and regulatory personnel to the threats of SHB not only for its directly negative impact on bee health but also for its ability to transmit viral diseases in bee colonies.
    • Entombed pollen: A new condition in honey bee colonies associated with increased risk of colony mortality 
      • Synopsis: Here we describe a new phenomenon, entombed pollen, which is highly associated with increased colony mortality. Entombed pollen appears as sunken, wax-covered cells amidst "normal", uncapped cells of stored pollen, and the pollen contained within these cells is brick red in color. The increased incidence of entombed pollen in reused wax comb suggests that there is a transmittable factor common to the phenomenon and colony mortality. In addition, there were elevated pesticide levels, notably of the fungicide chlorothalonil, in entombed pollen. Additional studies are needed to determine if there is a causal relationship between entombed pollen, chemical residues, and colony mortality.
    • Differential gene expression of the honey bee Apis mellifera associated with Varroa destructor infection
      • Synopsis: The parasitic mite, Varroa destructor, is the most serious pest of the western honey bee, Apis mellifera, and has caused the death of millions of colonies worldwide. Authors investigated whether Varroa infestation induces changes in Apis mellifera gene expression, and whether there are genotypic differences in the bee’s tolerance, as first steps toward unraveling mechanisms of host response and differences in susceptibility to Varroa parasitism. Results suggest that differences in behavior, rather than in the immune system, underlie Varroa tolerance in honey bees. They provide a first step toward better understanding molecular pathways involved in this particular host-parasite relationship.
    • A metagenomic survey of microbes in honey bee colony collapse disorder 
      • Synopsis: In Colony Collapse Disorder (CCD), honey bee colonies inexplicably lose all of their workers. CCD has resulted in a loss of 50-90% of colonies in beekeeping operations across the United States. The observation that irradiated combs from affected colonies can be repopulated with naïve bees suggests an infectious basis for CCD. One organism, Israeli acute paralysis virus (IAPV) of bees, was strongly correlated with CCD. The prevalence of IAPV sequences in CCD operations, as well as the temporal and geographic overlap of CCD and importation of IAPV infected bees from Australia, indicates that IAPV is a significant marker for CCD.
    • Honeybee colony collapse due to Nosema ceranae in professional apiaries 
      • Synopsis Honeybee colony collapse is a sanitary and ecological worldwide problem. To date there has not been a consensus about its origins. This report describes the clinical features of two professional bee-keepers affecting by this syndrome. Anamnesis, clinical examination and analyses support that the depopulation in both cases was due to the infection by Nosema ceranae (Microsporidia), an emerging pathogen of Apis mellifera. No other significant pathogens or pesticides (neonicotinoids) were detected and the bees had not been foraging in corn or sunflower crops. The treatment with fumagillin avoided the loss of surviving weak colonies. This is the first case report of honeybee colony collapse due to N. ceranae in professional apiaries in field conditions reported worldwide.
    • Recent Honey Bee Colony Declines 
      • Synopsis : In 2006, commercial migratory beekeepers along the East Coast of the United States began reporting sharp declines in their honey bee colonies. Current reports indicate that beekeepers in 35 states have been affected. Recent surveys indicate that about one-half of surveyed beekeepers have experienced "abnormal" or "severe" colony losses. To date, the potential causes of CCD, as reported by the scientists who are researching this phenomenon, include but may not be limited to the following: parasites, mites, and disease loads in the bees and brood; emergence of new or newly more virulent pathogens; poor nutrition among adult bees; lack of genetic diversity and lineage of bees; level of stress in adult bees (e.g., transportation and confinement of bees, or other environmental or biological stressors); chemical residue/contamination in the wax, food stores, and/or bees; and a combination of these and/or other factors.
    • IAPV, a bee-affecting virus associated with Colony Collapse Disorder can be silenced by dsRNA ingestion 
      • Synopsis: Colony Collapse Disorder (CCD) has been associated with Israeli acute paralysis virus (IAPV). CCD poses a serious threat to apiculture and agriculture as a whole, due to the consequent inability to provide the necessary amount of bees for pollination of critical crops. Here we report on RNAi-silencing of IAPV infection by feeding bees with double-stranded RNA, as an efficient and feasible way of controlling this viral disease. The association of CCD with IAPV is discussed, as well as the potential of controlling CCD. 
    • Behavioral attributes and parental care of Varroa mites parasitizing honeybee brood 
      • Synopsis: Varroa jacobsoni, an ectoparasite of the Asian honeybee Apis cerana, has been introduced world-wide, and is currently decimating colonies of the European honeybee Apis mellifera. Study describes here how a single fertilized female, infesting a brood cell, can produce two to four adult fertilized females within the limited time span of bee development (270 h in worker and 330 h in drone cells), despite the disturbance caused by cocoon spinning and subsequent morphological changes of the bee.
    • Nutritional stress due to habitat loss may explain recent honeybee colony collapses 
      • Synopsis: In spite of the tremendous public interest in the recent large honeybee losses attributed to colony collapse disorder, there is still no definitive explanation for the phenomenon. With the hypothesis that nutritional stress due to habitat loss has played an important role in honeybee colony collapse, study analyzes the land use data in United States to show that the colony loss suffered by each state is significantly predicted by the extent of its open land relative to its developed land area. Study also discusses how increasing loss of foraging resources could be synergistically acting with emerging diseases to stress honeybee populations and the importance therefore for preserving natural areas that act as important pollinator habitats.
    • Effects of neonicotinoid pesticide pollution of Dutch surface water on non-target species abundance 
      • MSc Thesis by Teresa C. van Dijk, 2010. 
        Sustainable Development Track Land use, Environment and Biodiversity (SD: LEB), Utrecht University

    Special Interest

    Partial list of key studies demonstrating the impacts of neonicotinoids and other pesticides on pollinators

    Authors/Date Pesticides Species Significance Daily News
    Sanchez-Bayo & Goka, 2014 Insecticides, acaricides, fungicides, herbicides A. mellifera, B. bombus Pyrethroids and neonicotinoids pose the highest risk by contact exposure of bees with contaminated pollen.  
    Zhu et al. 2014 Fluvalinate, coumaphos, chlorothalonil, chloropyrifos A. mellifera Combination of the four most common pesticides found in pollen/wax synergize, increase bee larvae mortality. Bee Larvae Adversely Affected by Mix of Pesticides and Inert Ingredients
    Carrillo et al. 2014 Fipronil, imidacloprid Africanized A. mellifera Learning, as evaluated through proboscis extention, is diminished. None
    European Food Safety Authority 2013 Imidacloprid, clothianidin, thiamethoxam A. mellifera Identifies a number of risks associated with the use of seed treatments that pose unaccpetable hazards to bees. The report led to a two-year suspension. Victory in Europe! EU Votes to Ban Bee-Killing Pesticides
    Di Prisco et al. 2013 Clothianidin A. mellifera Altered immune response allowed replication of viral pathogens in exposed bees. New Study Links Neonicotinoids to Bee Virus
    Goulson 2013 Clothianidin, thiamethoxam, imidacloprid A. mellifera Reviews the environmental risks of these chemicals to bees, birds, and beneficials. New Study Exposes Range of Harm from Neonicotinoid Pesticides
    Bryden et al. 2013 Imidacloprid B. bombus Chronic sublethal stress causes bee colony failure according to models. Scientists Link Pesticide-Related Stress to Bee Colony Collapse
    Williamson & Wright 2013 Clothianidin, coumaphos A. mellifera Long term memory, short-term memory, and odor differentiation all decrease. Studies Find that Pesticides Cause Brain Damage in Bees
    Palmer et al. 2013 Imidacloprid, clothianidin, organophosphate miticides A. mellifera Cognitive damage from exposure causes "epileptic type" hyperactivity with implications for survival. Studies Find that Pesticides Cause Brain Damage in Bees
    Matsumoto 2013 Clothianidin, dinotefuran, etofenprox, fenitrothion A. mellifera

    Demonstrates behavioral changes and declines in homing success.

    Derecka et al. 2013 Imidacloprid A. mellifera Metabolizing genes for honeybee larvae reduce at low levels of exposure. None
    Byrne et al. 2013 Imidacloprid A. mellifera Citrus tree flowers and nectar expose honey bees to the chemical at elevated levels for prolonged periods. None
    Hatjina, et. al. 2013 Imidacloprid A. mellifera Of the few physiological studies this finds sublethal doses decrease phyopharyngeal glands & respiratory rhythm. None
    Gill et al. 2012 Imidacloprid, lambda-cyhalothrin B. bombus Combination of two pesticides impairs foraging, increases worker mortality, and reduces colony success. Latest Study Again Links Pesticides to Bee Die-Offs
    Krupke et al. 2012 Clothianidin, thiamethoxam, metochlor, azoxystrobin A. mellifera Implicated seed treatments as an exposure pathway. None
    Henry et al. 2012 Thimethoxam A. mellifera Foraging success and survival in honey bees diminished. Two Studies Link Pesticides to Bee Health, Strengthen Case for Ban
    Whitehorn et al 2012 Imidacloprid B. terrestris Field realistic levels drastically reduce queen production and growth rates. Two Studies Link Pesticides to Bee Health, Strengthen Case for Ban
    Schneider et al 2012 Imidacloprid, clothianidin A. mellifera Sublethal exposure to these chemicals impacts foraging.  
    Congressional Research Service 2012 Multiple pesticides A. mellifera Summary of scientific studies and regulatory activity, identifies impacts to bee health: pesticides, pests and diseases, diet and nutrition, genetics, habitat loss, and beekeeper issues. Report Cites Multiple Causes, including Pesticides, of Declines in Bee Population
    Eiri & Nieh 2012 Imidacloprid A. mellifera Sublethal doses affects honey bee waggle dance, required for communicating food sources. None
    Tapporo et al. 2012 Neonicotinoids A. mellifera An underestimated route of exposure--atmospheric emission of particulate matter--demonstrate lethal effects None