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Diflubenzuron The
chlorinated diphyenyl compound, Diflubenzuron, better known by its trade
name DimilinTM, is an insect growth regulator. Diflubenzuron
can be found as a soluble concentrate, flowable concentrate, wettable
powder, or pellet (U.S. EPA 1997). All wettable powder diflubenzuron
products are classified as a Restricted Use Pesticide, meaning for
certified applicator use only, by EPA due to its severe toxicity to
aquatic organisms and other hazards to wildlife (University of MD 2000). Mode
of Action
Diflubenzuron
works by preventing the formation of chitin, a molecule necessary to the
formation of an insect’s cuticle or outer shell. Insects that absorb a
dose of diflubenzuron cannot form their protective outer shell and die
during molting. It is particularly effective against insect larva, but
also acts as an ovicide, killing insect eggs (U.S. EPA 1997). Toxicity
According
to industry tests, diflubenzuron does not pose a high risk of acute
toxicity to mammals. The oral LD50 (dose needed to kill 50% of
the animals tested) is greater than 4.64 g/kg in rats and mice and the
dermal LD50 is 4.64 g/kg in rabbits. However, EPA has given it
a toxicity class III rating (out of a scale of I to IV, I being the
highest toxicity class) with the signal word CAUTION, because it does
cause skin and eye irritation. Methemoglobinemia
and sulphemoglobinemia, indicating an impairment of the oxygen carrying
capacity of the blood, were seen in many studies (acute, sub-acute, sub
chronic, and chronic). Moderate amounts of diflubenzuron fed to day-old
ducks for 90 days showed decreased testosterone levels after 42 days (EXTOXNET
2001). Also, 2.5 parts per million of diflubenzuron in a diet fed to
growing chickens was shown to depress testosterone levels.
Diflubenzuron
has not been found to be mutagenic in short-term tests. However, when
halogenated compounds (molecules containing either chlorine, bromine,
fluorine or iodine) like diflubenzuron are tested in short-term tests,
results of ten correlate poorly with carcinogenicity in animal assays.
Environmental
Effects
The
major environmental hazard posed by diflubenzuron is its non-selective
toxicity to insects, including beneficials like the parasitic wasp.
Diflubenzuron is also highly toxic to both aquatic invertebrates and
crustaceans because they are both chitin producers. The LC50
(concentration needed to kill 50% of the test population) for the common
water-flea is 1.5 ppb (parts per billion) and blue crab reproduction is
impaired at even lower concentrations with an LC50 of only
0.5ppb. Environmental
Fate
Diflubenzuron’s
fate in water depends on the pH of the water. It degrades most rapidly in
alkaline water (half life is 1 day) and more slowly in acidic water (half
life is 16+ days). The half-life in soil is between four days and four
months, depending on the particle size. However, on leaf surfaces,
diflubenzuron is very stable. One study reports that even thirty to sixty
days after treatment, 90% of the intact pesticide could be detected on
leaves (Willcox and Coffey 1978). Plus, a small of amount of diflubenzuron
in soil will break down into 4-chloroaniline (PCA), which rapidly binds to
the soil (ETN 1996). Data
Gaps
In
1997, a Reregistration Eligibility Document was created for diflubenzuron.
Data regarding the ecological effects, acute toxicity and occupational and
residential exposures are needed for this pesticide (U.S. EPA 1997). References: Extension
Toxicology Network (ETN). 1996. Pesticide Information Profiles:
Diflubenzuron. Maddox,
J.D. 1982. “Use of insect Pathogens in pest management.” Introduction
to Pest Management. New York, NY. Madrid,
F.J. and R.K. Stewart. 1981. “Impact of diflubenzuron spray on gypsy
moth parasitoids in the field.” Journal of Economic Entomology
74:1-5. Opdyck,
J.C., et al. 1982. “Metabolism and fate of diflubenzuron in swine.” Journal
of Agriculture Food Chemistry 30:1223-1227. U.S.
EPA. 1979. Diflubenzuron decision document. Office of Pesticide Programs.
Washington, DC. U.S.
EPA. 1984. Tox One-liner No. 346A-diflubenzuron. Office of Pesticide
Programs. Washington, DC. U.S.
EPA. 1997. Reregistration Eligibility Document: diflubenzuron.
Office of Pesticide Programs. Washington, DC. <http://www.epa.gov/REDs/#D>. University
of Maryland, MD Cooperative Extension. 2000. “Restricted Use
Pesticides.” <http://pest.umd.edu/spatc/Leaflets/>. Verloop,
A. et al. 1977. “Benzoylphenyl urea-a new group of larvicides
interfering with chitin synthesis.” Pesticide Chemistry in the
Twentieth Century 37:237-270. Washington D.C. Willcox and Coffey, USDA-FS. 1978. “Environmental impacts of diflubenzuron (DimilinTM) insecticides.” Northeast Area State and Private Forum.
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BEYOND PESTICIDES |
