Monitoring Susceptibility to Azinphosmethyl in Field Populations of the Codling Moth (Lepidoptera: Tortricidae) with Pheromone Traps

Abstract

A procedure was developed to screen field populations of Cydia pomonella (L.) directly for resistance to azinphosmethyl or other toxicants. Male moths were collected in the field with pheromone traps and assayed with azinphosmethyl by topical application to the dorsal thorax directly on the adhesive-coated trap surface. The first flight had a steeper concentration-mortality regression than the second flight, indicating an increase in variability of the toxicological response over the season. The LC50 of moths trapped during the spring flight was somewhat higher (0.22 µg/moth) than during the summer (0.08–0.16 µg). Assays of laboratory-reared moths from the same location kept in plastic cages or on sticky trap surfaces to simulate the test procedure with field-collected moths yielded LC50’s in the same range (0.10–0.14 µg/moth). The longevity of moths and their toxicological response was not affected by the polybutene adhesive provided it was applied as a thin uniform film to the trap surface. Susceptibility to azinphosmethyl increased considerably with age in both sexes and was not correlated with loss in body weight. Female moths were slightly more susceptible when azinphosmethyl was applied to the thoracic venter instead of the dorsum. Males were equally susceptible to either application.