FIELD SELECTION FOR ESFENVALERATE RESISTANCE BY THE COLORADO POTATO BEETLE

Five insecticide application regimes were evaluated for two years to determine their influence on the development of esfenvalerate resistance by the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say). These included sequential applications of esfenvalerate; two alternated uses of esfenvalerate, azinphosmethyl, endosulfan, oxamyl, and Bacillus thuringiensis or cryolite; an IPM program; and one early season esfenvalerate application. Both CPB adults and first instars were tested for esfenvalerate resistance before and after insecticide applications. The LC50's in the early 1992 season were correlated with values in the late 1991 season. However, over the winter, esfenvalerate resistance of CPB adults decreased, but was relatively stable for first instars. Esfenvalerate LC50's late in the season were generally higher than values early in the season. Increases in esfenvalerate LC50's were correlated with the number of esfenvalerate applications made in these fields during the growing season, with the greatest increase found in the sequential esfenvalerate treatment.