Insensitive Acetylcholinesterase and Esterase Polymorphism in Susceptible and Resistant Populations of the Tobacco Whitefly Bemisia tabaci (Genn.)

Insecticide-sensitive and insensitive acetylcholinesterase (AChE) variants in individual adult whitefly were identified on the basis of their sensitivities to inhibition by paraoxon and azamethiphos in a microplate assay. The technique has been used successfully to monitor whitefly populations from a wide geographical area from crops of both horticultural and agricultural importance and has so far identified a sensitive and two insensitive AChE variants. The frequencies of the three variants can be assessed most reliably from a bivariate plot of mean percentage activity remaining in the AChE of haploid males after inhibition by these two insecticides. All populations of whitefly, including those from the United Kingdom, contained a large proportion of individuals with insensitive AChE capable of conferring extremely high resistance. Esterase polymorphism was also examined in these same populations using polyacrylamide gel electrophoresis. Although this identified several banding patterns, one form predominated, the so-called "B-type" originally found on poinsettia in the southern United States. The same esterase pattern was found in populations from the Middle East, Central America, and Northern Europe.