Acute contact toxicity of insecticidal baits on honeybees Apis mellifera: a laboratory study

Abstract

The honeybee Apis mellifera L. (Hymenoptera: Apidae) is an important pollinator, an object of human economic activity and a bioindicator of environmental pollution. Insecticides used in Agriculture for treatment of plants, bee colonies, and farm animals may be dangerous for bees. This paper reports the results of a comparative assessment of the acute contact toxicity of four toxic bait formulations designed for insect pest control on livestock farms to the honeybees. Toxic baits consisted acetamiprid, ivermectin, chlorfenapyr, and fipronil, with residues of which on the filter paper adult bees contacted on plastic containers. It was found that the bait formulation with ivermectin manifested toxicity slower than the other ones. We used probit analysis to calculate median lethal doses (LD50) of each active substance showed that their toxicity to bees decreased in the following order: fipronil-ivermectin-chlorfenapyr-acetamiprid. Considering the mass content of active substances in formulations, median lethal doses of toxic baits were 202.6 μg/bee (bait with fipronil), 229.3 μg/bee (bait with ivermectin), 1188.3 μg/bee (bait with chlorfenapyr), and 6552 μg/bee (bait with acetamiprid). Thus, bait formulations themselves may be considered practically non-toxic to bees, since their LD50 exceeded the threshold value of 100 μg/bee. Assessment of hazard degree for bees by the hazard index showed that the insecticide bait containing acetamiprid were less dangerous than the other three bait formulations under laboratory conditions. The future semi-field and field studies are needed to evaluate the possible exposure and the hazard degree of insecticidal baits for bees under conditions close to practice use of these formulations.