Assessment of risk to hoary squash bees (Peponapis pruinosa) and other ground-nesting bees from systemic insecticides in agricultural soil

Abstract

Using the hoary squash bee ( Peponapis pruinosa ) as a model, we provide the first probabilistic risk assessment of exposure to systemic insecticides in soil for ground-nesting bees. To assess risk in acute and chronic exposure scenarios in Cucurbita and field crops, concentrations of clothianidin, thiamethoxam and imidacloprid (neonicotinoids) and chlorantraniliprole (anthranilic diamide) in cropped soil were plotted to produce an environmental exposure distribution for each insecticide. The probability of exceedance of several exposure endpoints (LC 50 s) was compared to an acceptable risk threshold (5%). In Cucurbita crops, under acute exposure, risk to hoary squash bees was below 5% for honey bee LC 50 s for all residues evaluated but exceeded 5% for clothianidin and imidacloprid using a solitary bee LC 50 . For Cucurbita crops in the chronic exposure scenario, exposure risks for clothianidin and imidacloprid exceeded 5% for all endpoints, and exposure risk for chlorantraniliprole was below 5% for all endpoints. In field crops, risk to ground-nesting bees was high from clothianidin in all exposure scenarios and high for thiamethoxam and imidacloprid under chronic exposure scenarios. Risk assessments for ground-nesting bees should include exposure impacts from pesticides in soil and could use the hoary squash bee as an ecotoxicology model.

Neonicotinoid exposure affects foraging, nesting, and reproductive success of ground-nesting solitary bees

“…This species exhibits an unusually high degree of dietary specialization, depending entirely upon Cucurbita crops (Cucurbitaceae) for pollen across most of its range 22,23,25 . Each hoary squash bee female constructs its own nest in the ground 26,27 , commonly within cropping areas 10 where systemic insecticides are often applied as soil drenches or seed treatments 8 .…”

“…While all bees that forage on treated crops may be at risk of exposure to systemic pesticide residues in pollen and nectar 28,29 , there is an additional risk of exposure to residues in soil for ground-nesting bees 4,8 . This route of pesticide exposure is currently not considered in regulatory environmental risk assessments for pollinators because honeybees rarely come into direct contact with soil 3,4,7,8 .…”

“… Despite their indispensable role in food production 1,2 , insect pollinators are threatened by multiple environmental stressors, including pesticide exposure 2-4 . Although honeybees are important, most pollinating insect species are wild, solitary, ground-nesting bees 1,4-6 that are inadequately represented by honeybee-centric regulatory pesticide risk assessment frameworks 7,8 . Here, for the first time, we evaluate the effects of realistic exposure to systemic insecticides (imidacloprid, thiamethoxam or chlorantraniliprole) on a ground-nesting bee species in a semi-field experiment.…”

“…Here, for the first time, we evaluate the effects of realistic exposure to systemic insecticides (imidacloprid, thiamethoxam or chlorantraniliprole) on a ground-nesting bee species in a semi-field experiment. Hoary squash bees ( Eucera ( Peponapis ) pruinosa ) provide essential pollination services to North American pumpkin and squash crops 9-14 and commonly nest within cropping areas 10 , placing them at risk of exposure to pesticides in soil 8,10 , nectar and pollen 15,16 . Hoary squash bees exposed to an imidacloprid-treated crop initiated 85% fewer nests, left 84% more pollen unharvested, and produced 89% fewer offspring than untreated controls.…”

Biotic and Abiotic Factors Associated with Colonies Mortalities of Managed Honey Bee (Apis mellifera)

“…Krupke, et al [97] considered different routes of contamination of beehives with neonicotinoids but focused primarily on the use of coated seeds and granules, which contaminate the soil. Yang, et al [98] found a negative effect of sublethal doses of imidacloprid on honey bee behavior. Feeding individuals with sugar syrup containing 50 µg/L has shown to prolong the time interval between two visits to the feeding site [99,100].…”