EFFECT OF AMITRAZ ON COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE) FEEDING, DEVELOPMENT AND SURVIVAL

Effects of amitraz, a formamidine insecticide, were studied in Colorad o potato beetle, Leptinotarsa decemlineata (Say), populations from Min nesota, North Dakota and Virginia Contact exposure or ingestion of lea ves dipped in 4000 ppm amitraz was not lethal to adults. However, adul t feeding was reduced 50% upon exposure to 90 ppm amitraz, a rate < 1/ 8 that recommended by the manufacturer for testing as a foliar insecti cide. Ingestion of foliage treated with 945 ppm amitraz by early insta r larvae had long-term effects on Colorado potato beetle development a nd survival delaying adult emergence 4.7 days and causing 87% mortalit y. In 72 h bioassays, LC(50)s by contact exposure or ingestion were > 3.2X the suggested held rate. LC(50)s determined by exposure of larvae to treated foliage were greater than LC(50)s determined by immersing larvae. Egg hatch was not reduced by application of less than or equal to 1840 ppm amitraz. In field trials, amitraz reduced defoliation as effectively as esfenvalerate, the insecticide of choice when these tri als were conducted. Amitraz-treated plots had yields intermediate betw een esfenvalerate and control treatments.