Laboratory determination of particulate-matter-bound agrochemical toxicity among honeybees, mason bees, and painted lady butterflies.

Pollinator population declines are global phenomena with severe consequences for native flora and agriculture. Many factors have contributed to pollinator declines including habitat loss, climate change, disease and parasitism, reductions in abundance and diversity of foraging resources, and agrochemical exposure. Particulate matter (PM) serves as a carrier of toxic agrochemicals, and pollinator mortality can occur following exposure to agrochemical-contaminated PM. Therefore, laboratory-controlled experiments were conducted to evaluate impacts of individual PM-bound agrochemicals. Honeybees (Apis mellifera), blue orchard mason bees (Osmia lignaria), and painted lady butterfly (Vanessa cardui) larvae were exposed to bifenthrin, permethrin, clothianidin, imidacloprid, abamectin, and ivermectin via suspended, airborne PM. Agrochemical concentrations in PM to which pollinators were exposed were based on concentrations observed in fugitive beef cattle feedyard PM including a "mean" treatment and a "max" treatment reflective of reported mean and maximum PM-bound agrochemical concentrations, respectively. In general, pollinators in the mean and max treatments experienced significantly higher mortality compared to controls. Honeybees were most sensitive to pyrethroids, mason bees were most sensitive to neonicotinoids and painted lady butterfly larvae were most sensitive to macrocyclic lactones. Overall, pollinator mortality was quite low relative to established toxic effect levels derived from traditional pollinator contact toxicity tests. Further, pollinator mortality resulting from exposure to individual agrochemicals via PM was less than that reported to occur at beef cattle feedyards highlighting the importance of mixture toxicity to native and managed pollinator survival and conservation.