Genetic and biological influences in the evolution of insecticide resistance.

Evolution of insecticide resistance, measured by the though the rate at which this occurred varied. The slowfrequency of a resistant allele and by population size, was est response to selection occurred when (I) the populasimulated on a computer. The effects of dominance, tion was diluted by immigrants, (2) population density initial gene frequency, refugia, immigration, and reprowas drastically suppressed by severe selection, and (3) ductive potential were studied singly with a deterministic susceptible individuals had a reproductive advantage over model. In all cases, resistance evolved eventually, altheir resistant counterparts. More than 364 species of arthropods have developed resistance to insecticides over the past 30 years (Georghiou and Taylor I977a) . The main weapon for countering this resistance has been use of alternative chemicals with structures that are unaffected by cross resistance. However, the gradual depletion of substitute chemicals, as resistance to these also developed, has revealed the limitations of this practice and has emphasized the need for maximizing the "useful life" of new chemicals through their application under conditions that delay or prevent the development of resistance. To achieve this goal, it is essential to understand the parameters influencing the selection process. One classification of the many factors involved, which we proposed earlier (Georghiou and Taylor] 977a) , is as follows: A. Genetic Frequency of R alleles N umber of R alleles Dominance of R alleles Penetrance; expressivity; interactions of R alleles Past selection by other chemicals Extent of integration of R genome with fitness factors B. Biologica] Biotic Generation turn-over Offspring per generation Monogamy fpolygamy; parthenogenesis Behavioral Isolation; mobility; migration Monophagy / pol yphagy Fortuitous survival; refugia