11: Sublethal pesticide exposure increases development time and reduces the rate of weight gain in Japanese orchard bee (Osmia cornifrons) larvae

Solitary bees are exposed to various chemicals applied for pest management while pollinating crops. There is an unmet need to study sublethal toxicity of agricultural pesticides on solitary bees as increasing evidence is suggesting that bees from other families do not respond to pesticides in the same way as social bees. Conducting such studies with solitary bees has been difficult, because of the need for thousands of test subjects and due to the single generation of solitary bees. It is even more difficult to conduct larval bioassays because of the difficulties in obtaining eggs or young larvae. This study examined the effects of four widely used plant systemic pesticides on Osmia cornifrons (Hymenoptera: Megachilidae). Pollen stores from the nests of this solitary bee were collected in large numbers in which we incorporated different doses of three insecticides (acetamiprid, flonicamid, and sulfoxaflor) and a fungicide (dodine) and exposed eggs in artificial rearing chambers. After egg hatch, larvae were allowed to feed on the pollen-mass treated with known concentrations of the pesticides, and various effects caused by the chronic ingestion of contaminated pollens were measured until adult eclosion. This year-long study reveals that the sublethal exposure of systemic pesticides could cause delayed larval development and lower body weights at higher concentrations. In addition, exposure to the systemic fungicide dodine caused delayed mortality and abnormal larval defecation, indicating potential threats to bees. These findings could be helpful in understanding and mitigating the effects of systemic pesticides on other species of solitary bees.