Laboratory toxicology of six forestry insecticides to four species of bee (hymenoptera: Apoidea)

Laboratory dose-response studies were conducted with four species of adult bees, Apis mellifera (workers), Andrena erythronii (females), Megachile rotundata (females), and Bombus terricola (workers), using six insecticides, permethrin, mexacarbate, aminocarb, fenitrothion, carbaryl, and trichlorfon. All insecticides were applied topically to the thorax of the bees as technical grade in an acetone carrier. Mortality was accumulated over 48 h, and probit analyses were conducted separately on data sets expressed in units of gAI (active ingredient)/g body weight and of gAI/bee. LD₅₀ values with 95% confidence limits and slopes with standard errors are provided for each bee/insecticide combination in each data set. Relative toxicities, relative susceptibilities, and fresh body weights are also provided. The analysis in units of gAI/g body weight indicated that the insecticides were typically ranked in order of decreasing toxicity—permethrin, mexacarbate, aminocarb, fenitrothion, carbaryl, and trichlorfon. Likewise, the bees ranked from the most to least susceptible in the order of A. mellifera, A. erythronii, M. rotundata and B. terricola. Trends within the data set for units of gAI/bee were less consistent. These data are discussed and compared with other published data on the toxicology of insecticides to bees and from the perspective of risk assessment.