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 (LC50s) 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 LC50s for all residues evaluated but exceeded 5% for clothianidin and imidacloprid using a solitary bee LC50. 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 soil and could use the hoary squash bee as an ecotoxicology model.

Supplemental forage ameliorates the negative impact of insecticides on bumblebees in a pollinator-dependent crop

“…This is not particularly surprising since the insecticide was applied as a soil drench, rather than a foliar spray, and the product moved systemically through the plant to reach flowers. As a result, soil exposure is likely to pose a threat to ground-nesting wild bees that come in close contact with these residues [42–44]; however, given that bumblebees were housed in aboveground structures in the experiment, we assume that insecticide detected in nest materials derived from oral exposure via collection of contaminated floral resources. The specific concentrations reported for imidacloprid in crop-treated pollen were high (median in watermelon: 75.4 ng g −1 ) but within the range detected in other studies of neonicotinoids in cucurbits [45–47].…”

Nesting habitat of ground‐nesting bees: a review

“…Although ground‐nesting bees can be found in many different natural environments, most are unwilling to nest in captivity. One exception is the squash bee, Peponapis pruinosa , which has consequently been used as a model species in many studies (Julier & Roulston, 2009; Ullmann et al ., 2016; Willis Chan et al ., 2019). These bees tolerate a broad range of soil conditions, as long as they have access to their host plant, Cucurbita spp.…”

“…Such research would be especially valuable in agricultural systems, where farming practices can involve mixing the soil to a depth of up to 40 cm during tillage, and the use of agrochemicals to combat insect pests. A few papers have investigated the effect of tillage (Ullmann et al ., 2016; Skidmore et al ., 2019), irrigation (Julier & Roulston, 2009) and pesticides (Willis Chan et al ., 2019) on ground‐nesting bees, but more research is needed on different species of ground‐nesters, other than squash bees, and their reproductive output. We still know little about the effects of agrochemicals on survival of ground‐nesting bees, whether at the underground larval stages or as adults, but recent studies have begun to show impacts of pesticides on bees through exposure to contaminated soil (Anderson & Harmon‐Threatt, 2019; Willis Chan et al ., 2019).…”

“…A few papers have investigated the effect of tillage (Ullmann et al ., 2016; Skidmore et al ., 2019), irrigation (Julier & Roulston, 2009) and pesticides (Willis Chan et al ., 2019) on ground‐nesting bees, but more research is needed on different species of ground‐nesters, other than squash bees, and their reproductive output. We still know little about the effects of agrochemicals on survival of ground‐nesting bees, whether at the underground larval stages or as adults, but recent studies have begun to show impacts of pesticides on bees through exposure to contaminated soil (Anderson & Harmon‐Threatt, 2019; Willis Chan et al ., 2019). There are also many unanswered questions related to the impacts on bee populations of agricultural machinery in settings that could be attractive nesting habitat for ground‐nesters, but that could act as ecological traps if nests are subsequently destroyed.…”

Impact of Biotic and Abiotic Stressors on Managed and Feral Bees

“…(3) Parasites, pathogens, and pests that naturally afflict bees and vector bee diseases have rapidly spread and developed resistance to control tactics [66,67]. (4) Dramatic increases in (a) pesticide applications in agricultural systems to control insect pests [68,69], (b) honey bee hives to control bee pests and diseases [70,71] as a result of their resistance development, and (c) pesticide residues in nesting materials used by non- Apis species [72,73] simultaneously expose bees to these chemistries. (5) Human-mediated bee movements have been linked to inducing colony stress, introducing foreign parasites, and increasing resource competition for native bees [74,75,76].…”