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Insect Growth
Regulators Insect
Growth Regulators (IGRs), also called third-generation insecticides, are
pesticides that disrupt the normal activity of the endocrine or hormone
system of insects, affecting the development, reproduction, or
metamorphosis of the target insect. They have a much slower mode of action
than synthetic chemical insecticides. IGRs include juvenile hormone (JH)
mimics and chitin synthesis inhibitors (CSIs). There
is a large concern about the effect of IGRs on non-target species and many
IGRs are lacking full health and safety data. Juvenile
Hormones (JH) Most
currently registered IGRs, such as hydroprene
and methoprene, fall into the juvenile hormone
mimic category. These pesticides mimic the JH produced in the insect brain,
which forces the insect to remain in a juvenile state. Normally, the production
of the JH would ebb as the insect progressed through the nymphal stages
until the final molt into the adult stage, when JH production would cease.
When exposed to a JH mimic, the insect remains in an immature state, and
is rendered unable to successfully molt into the adult stage or become
reproductively viable. JH
mimics are not be specific to the pest under attack, as the molecules
based on the JH system are more or less common to all insect species. Chitin
Synthesis Inhibitors (CSIs) CSIs,
such as hexaflumuron, lufenuron and diflubenzuron,
inhibit the production of chitin, a major component of the insect exoskeleton.
Insects treated with CSIs become unable to synthesize new cuticle, and
therefore unable to successfully molt into the next stage. CSIs
may be toxic to other arthropods, and IGR metabolites may have adverse
effects on vertebrates due to their ability to bind to certain members of
the nuclear hormone receptor family.
Pest Resistance to IGRsIt
was originally thought that insects would be unable to develop resistance
to molecules that mimic their own hormones, but there is already evidence
of developing resistance to several IGRs, including methoprene, hydroprene,
kinoprene, pyriproxifen, and diflubenzuron. Resistance seems to result
from decreased penetration and increased metabolism of the compound. For
additional toxicity information, please see fact sheets on individual
IGRs: diflubenzuron, hexaflumuron,
hydroprene and methoprene.
Resource: Hoffman,
K.H., Lorenz, M.W. 1998. Recent Advances in Hormones in Insect Pest
Control. Phytoparasitica 26:4.
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BEYOND PESTICIDES |
