The effect of sub-lethal pesticide exposure on pollination-relevant bee foraging behaviors across a species richness gradient
Neonicotinoid pesticides, which have become the most widely used class of insecticides, are highly toxic to bees and have been shown to negatively impact bee behavior at very low levels. For instance, sub-lethal exposure may have negative impacts on worker lifespan, colony weight, and pollen collection. Yet we have little understanding of how sub-lethal neonicotinoid exposure affects bee behaviors important for pollination at both individual and community levels. At the individual level, floral fidelity, where bees temporarily specialize on one flower species, is particularly important for plant reproduction since it allows for conspecific pollen transfer. At the community level, visitation evenness is important as it allows all plant species to receive pollination services. We examined the impacts of neonicotinoid pesticides on pollination-relevant behaviors in the presence or absence of field-realistic pesticide exposure across a species richness gradient using both social (Bombus impatiens, Apis melifera) and solitary bees (Osmia lignaria, Megachile rotundata). We performed laboratory foraging experiments in an automated chamber with artificial flowers and built-in RFID tag readers that allowed for exact tracking of bee movements.
We continue to gather data, but preliminary results show that floral fidelity is reduced by sub-lethal pesticide exposure in both social and solitary bees. In a multiple species context, we found a significant interaction between pesticide exposure and species richness for both visitation evenness and floral fidelity. In the absence of pesticides, we found that greater species richness increased visitation evenness, though impacts on floral fidelity varied greatly by species identity. In the presence of pesticides, species richness had a reduced impact on bee foraging behaviors. Specifically, we found that smaller-bodied solitary bees were disproportionately impacted by sub-lethal neonicotinoid exposure compared to larger-bodied bumble bees (Bombus), which disrupted competitive outcomes. This indicates that neonicotinoid pesticides may decrease the quality of pollinators in terms of plant pollination services. These results are important for furthering our understanding of how chemical disruptions modulate biodiversity-ecosystem functioning relationships driven by plastic behaviors. Improved understanding in this field will be vital for informing pesticide management while promoting sustainable agriculture and preservation of pollinator-dependent plant communities.