Development of a rapid resistance monitoring bioassay for codling moth

The codling moth, Cydia pomonella (L.), is the most important apple pest worldwide. Due to internal larval feeding and high crop value, the economic threshold for this pest is essentially zero. Thus, it is not surprising that codling moth resistance is wide spread in many apple growing regions around the world and for a variety of chemical groups. Although there are valid methods to monitor for codling moth resistance, such as larvae exposed to treated artificial diet or topical application of insecticide to diapausing larvae, they usually take months to complete. Therefore, information obtained from these bioassays is usually not available to growers in the same year. As a result, a rapid method was developed to monitor for codling moth resistance. Different codling moth populations were established in the laboratory, including two colonies that were highly resistant to methoxyfenozide, from infested apples collected from commercial orchards in 2007. Novel sixteen-well bioassay plasticware was designed containing lyophilized codling moth diet, and seven different insecticides concentrations were used for the bioassays. Mortality data were obtained 3 and 4 days later for fourth instars and neonates, respectively. A single diagnostic dose was calculated across different susceptible populations and larval stages (neonate and fourth instar). This single diagnostic dose will be later tested against larvae extracted from infested apples from different orchards, including orchards with a known history of insecticide failures to validate a new assay kit for the convenient and rapid detection of insecticide resistance.