Effect of Amitraz on Colorado Potato Beetle (Coleoptera: Chrysomelidae) Feeding, Development and Survival

Abstract

Effects of amitraz, a formamidine insecticide, were studied in Colorado potato beetle, Leptinotarsa decemlineata (Say), populations from Minnesota, North Dakota and Virginia. Contact exposure or ingestion of leaves dipped in 4000 ppm amitraz was not lethal to adults. However, adult feeding was reduced 50% upon exposure to 90 ppm amitraz, a rate <1/8 that recommended by the manufacturer for testing as a foliar insecticide. Ingestion of foliage treated with 945 ppm amitraz by early instar larvae had long-term effects on Colorado potato beetle development and survival, delaying adult emergence 4.7 days and causing 87% mortality. In 72 h bioassays, LC50s by contact exposure or ingestion were > 3.2× the suggested field rate. LC50s determined by exposure of larvae to treated foliage were greater than LC50s determined by immersing larvae. Egg hatch was not reduced by application of ≤ 1840 ppm amitraz. In field trials, amitraz reduced defoliation as effectively as esfenvalerate, the insecticide of choice when these trials were conducted. Amitraz-treated plots had yields intermediate between esfenvalerate and control treatments.