FIELD SELECTION FOR ESFENVALERATE RESISTANCE BY THE COLORADO POTATO BEETLE

Five insecticide application regimes were evaluated for two years to d etermine their influence on the development of esfenvalerate resistanc e by the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) . These included sequential applications of esfenvalerate; two alterna ted uses of esfenvalerate, azinphosmethyl, endosulfan, oxamyl, and Bac illus thuringiensis or cryolite; an IPM program; and one early season esfenvalerate application. Both CPB adults and first instars were test ed for esfenvalerate resistance before and after insecticide applicati ons. The LC50's in the early 1992 season were correlated with values i n the late 1991 season. However, over the winter, esfenvalerate resist ance of CPB adults decreased, but was relatively stable for first inst ars. Esfenvalerate LC50's late in the season were generally higher tha n values early in the season. Increases in esfenvalerate LC50's were c orrelated with the number of esfenvalerate applications made in these fields during the growing season, with the greatest increase found in the sequential esfenvalerate treatment.