The use of treated seeds with systemic agrochemicals represents a potential risk of chronic exposure for bees through pollen

Pesticides and drought are implicated in patterns of worldwide bee declines. Systemic pesticides applied to seeds can be transported to other tissues, including pollen and nectar, resulting in pollinator exposure during foraging. Pesticide exposure makes bees more susceptible to pathogen infections and behavioral changes with implications for survival and reproduction. In addition, drought may also affect pollinators by increasing pesticide concentrations in pollen and reducing the nutritional value of pollen and nectar. Thus, increasing drought frequency could negatively affect pollinators, but these effects are almost entirely unexplored.









We assessed how drought stress affects pesticide concentration in pollen of three major US crops whose seeds are treated with systemic pesticides: sunflower, cotton, and squash. Plants of each crop were randomly assigned to one of three drought treatments (well-watered, moderate water, and drought), and the pollen was tested for pesticides.









Out of 94 agrochemicals tested, the detections for the herbicide Metolachlor were exceptionally high across the three crops (Cotton 72 %, sunflower 80 %, and Squash 31%). Also, the neonicotinoid Thiamethoxam was detected in 93% of the squash across treatments, with medium and full irrigation treatments displaying the highest values. Importantly, the maximum concentrations detected of these two compounds were estimated to exceed the LD50s for bees in some of the samples.









Overall, we found that irrigation treatments did not influence pesticide concentrations in pollen across the three crops; however, we demonstrated that systemic pesticides accumulate in pollen, exposing pollinators to the cascade effects of chronic toxicity.