FIELD-EVALUATION OF INSECTICIDE APPLICATION STRATEGIES ON DEVELOPMENT OF INSECTICIDE RESISTANCE BY COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE)

Five insecticide application regimes were evaluated to investigate their influence on development of insecticide resistance in field populations of Colorado potato beetle, Leptinotarsa decemlineata (Say). These regimes included season-long sequential esfenvalerate applications; two alternate uses of esfenvalerate, azinphosmethyl, endosulfan, oxamyl, and Bacillus thuringiensis ssp. tenebrionis; an integrated pest management (IPM) program; and one early season esfenvalerate application. Response of Colorado potato beetle from each treatment to four insecticides was determined at the beginning and end of the growing season. A filter-paper technique was used to estimate the concentration-response relationship for first instars, and a topical application bioassay was used to measure response of adults. Differences in esfenvalerate susceptibility existed among treatments in the early season; these differences were correlated with frequency of esfenvalerate applications during the previous season. Populations from all field treatments at the end of season showed an increase in resistance to esfenvalerate and endosulfan but not to azinphosmethyl or oxamyl. Increases in resistance generally were related to the frequency that a specific chemical was applied. We observed significant correlations between increase in esfenvalerate resistance and number of esfenvalerate applications in a given regime; 10 applications resulted in a 3.6-fold increase. Direct selection by esfenvalerate appeared to be the primary factor in development of resistance in these populations. Consequently, we suggest that reduction of repeated pyrethroid use is critical for limiting resistance development. The lowest increase in esfenvalerate resistance was found in the IPM treatment, indicating that this management strategy was also effective in retarding resistance development.