Insecticide susceptibility of Japanese mason bees (Osmia spp.) versus that of the western honey bee (Apis mellifera)

Abstract

Acute toxicity of pesticides to wild bee species is inferred by using the LD₅₀ values of the western honey bee, Apis mellifera, as a standard baseline. However, substantial discrepancies are often reported between the LD₅₀ values for wild bees and those for A. mellifera. Here, we conducted tests to compare acute toxicity between Japanese mason bees (Osmia spp.) and the western honey bee. For nearly all tested insecticides, the mortality rates of mason bees were equivalent to, or slightly lower than, those of the western honey bee. However, the LD₅₀ of acetamiprid in male mason bees was approximately five-fold lower than that in workers of the western honey bee. These results suggest that, although the current pesticide risk assessment is generally conservative for Japanese mason bees, continued attention is warranted to ensure that their sensitivity—particularly to acetamiprid—remains within the presumed safety factor.