Phone: 614-292-5274 Fax: 614-292-9783
e-mail: extento@postoffice.ag.ohio-state.edu
William F. Lyon
Insect resistance to insecticides is an increasing problem. It happens as individually resistant insects survive, breed and pass on their resistant genes to their offspring. (A population of insects becomes resistant over a period of several generations .) Resistance develops more quickly under heavy doses of insecticides or very frequent application. The type of insect pest makes a difference on how fast resistance can develop. With social insects, such as ants, resistance is seldom a problem since usually only the queen is reproductive. With nonsocial insects such as fleas, each individual is reproductive and can allow resistance to develop more quickly. The time needed to become a reproductive adult also determines the development of resistance. The life cycle of the flea is only 21 to 28 days compared to an ant of about 10 to 12 months.
Different classes of insecticides provide different ways for resistance development. (Insecticides are broken down in bodies of resistant insects.) With carbamate and organophosphate insecticides, resistance occurs by one mechanism. With pyrethroid insecticides, three mechanisms of resistance have been identified, making resistance development more possible. Also, insect resistance to one insecticide can be cross-resistant to other insecticides of the same class or even of other insecticides having a similar mode of action. With pyrethroids, the mechanism of cross-resistance is complex, but common. While no resistance has been identified for insect growth regulators (IGRs), the potential exists. An ideal application will kill as many insects as possible without underdosing or overdosing. The only proven solution to resistance problems is to rotate the use of different chemical classes or families of insecticides.