A comparison of pollen and syrup exposure routes in Bombus impatiens (hymenoptera: apidae) microcolonies: implications for pesticide risk assessment

Bumble bees are important pollinators for both native plants and managed agricultural systems. Accumulating evidence has shown that pesticides, including neonicotinoids, can have a range of adverse effects on bumble bee health. Most laboratory studies that assess the effects of chronic neonicotinoid exposure on bumble bees dose syrup as the vehicle, rather than pollen. However, in the field, it is likely that bumble bees are exposed to neonicotinoids in both nectar (syrup) and pollen. To examine the potential for different effects based on the vehicle, we compared two studies of chronic exposure to acetamiprid in Bombus impatiens microcolonies. We found treatment related effects on the number of drones produced when acetamiprid was delivered via either syrup or pollen. In contrast, we found that average drone weight was affected at a range of doses only when microcolonies were exposed to acetamiprid via pollen. Furthermore, independent of the route of exposure, we identified associations between the timing of colony pollen consumption and drone emergence, suggesting that the number of drones produced mediates the demand for pollen. In general, our analyses point to the importance of the treatment vehicle and suggest that critical effects on developing brood could be missed when neonicotinoid exposure occurs only through syrup.

Impact/Purpose

Bumble bees are important pollinators for both native plants and managed agricultural systems. Accumulating evidence has shown that pesticides, including neonicotinoids, can have a range of adverse effects on bumble bee health. Most laboratory studies that assess the effects of chronic neonicotinoid exposure on bumble bees dose syrup as the vehicle, rather than pollen. However, in the field, it is likely that bumble bees are exposed to neonicotinoids in both nectar (syrup) and pollen. To examine the potential for different effects based on the vehicle, we compared two studies of chronic exposure to acetamiprid in Bombus impatiens microcolonies. We found treatment related effects on the number of drones produced when acetamiprid was delivered via either syrup or pollen. In contrast, we found that average drone weight was affected at a range of doses only when microcolonies were exposed to acetamiprid via pollen. Furthermore, independent of the route of exposure, we identified associations between the timing of colony pollen consumption and drone emergence, suggesting that the number of drones produced mediates the demand for pollen. In general, our analyses point to the importance of the treatment vehicle and suggest that critical effects on developing brood could be missed when neonicotinoid exposure occurs only through syrup. These results are important for informing approaches toward pesticide risk assessment.

Citation

Weitekamp, C., R. Koethe, AND D. Lehmann. A comparison of pollen and syrup exposure routes in Bombus impatiens (hymenoptera: apidae) microcolonies: implications for pesticide risk assessment. Entomological Society of America, Lantham, MD, 51(3):613-620, (2022). [DOI: 10.1093/ee/nvac026]

DOI: A comparison of pollen and syrup exposure routes in Bombus impatiens (hymenoptera: apidae) microcolonies: implications for pesticide risk assessment