Pesticide Transfer between Solitary Bee Nesting Materials and Provisions─Implications for Larval Exposure

Solitary cavity-nesting bees have unique life histories resulting in pesticide exposure routes, especially to larvae, that differ from social bees. Pesticides in nesting materials, such as leaves and soil, are hypothesized to transfer into food provisions, adding oral and contact exposure to pesticides for solitary bee larvae. The objective of this work was to determine if pesticides in nesting materials transfer into alfalfa leafcutting bee (ALCB) or blue orchard bee (BOB) provisions. We developed novel laboratory experiments for use in quantifying this. After 24 h, the pesticide concentrations transferred into ALCB provisions were 5792 ± 656 ng/g, 1140 ± 48 ng/g, and 41 ± 9 ng/g for the high chlorpyrifos, low chlorpyrifos, and lambda-cyhalothrin transfer experiments, respectively. After 168 h, the pesticide concentrations transferred into BOB provisions were 27 ± 3 ng/g and 51 ± 1 ng/g for bifenthrin and fluxapyroxad transfer experiments, respectively. In contrast, lambda-cyhalothrin uptake into BOB provisions was not observed. In these experiments, we determined that the nesting material contribution to overall pesticide exposure for ALCB larvae was in the range of concern, while that for BOB larvae was low, as the transferred concentrations from soil into provisions were minimal.