Determination of Susceptibility to Seven Insecticides Registered in Canada for the Control of the Colorado Potato Beetle (CPB), Leptinotarsa decemlineata Say

The 2017 insecticide susceptibility survey in Canadian populations of Colorado potato beetle (CPB) determined that forty percent of the tested CPB populations were resistant to the neonicotinoid insecticide, ACTARA® (thiamethoxam). A further fifty to sixty percent of the populations could be considered to have reduced susceptibility to thiamethoxam and a second neonicotinoid, TITAN™ (clothianidin), respectively. These results are not surprising as over 76% of the populations were collected from fields where neonicotinoid products have been applied within the past five years. Interestingly, two thirds of populations tested with the butenolide product SIVANTO® PRIME (flupyradifurone), registered only two seasons prior to the survey, showed reduced susceptibility. The majority of CPB populations where reduced susceptibility or resistance to flupyradifurone was observed were also found to be resistant or less susceptible to neonicotinoids. At present, only thirty percent of the CPB populations have been tested with spinosyn (ENTRUST™ and DELEGATE®) and anthranilic diamide (CORAGEN™ and VERIMARK®) insecticides. All were susceptible to spinosyns, but only 20% remained susceptible to diamides. In the three cases where susceptibility to diamides was reduced or resistance was observed, either diamide products had previously been applied or there was reduced susceptibility or resistance to neonicotinoid products in the same populations. Based on the survey findings, cross-resistance among insecticide classes, and possibly between classes, should be an issue of concern for potato growers in the coming season.