Quantifying the Risks of Pesticide Exposure to Squash Bee Behavior and Pollination Services

View the project final report

Commodities

• Animals: bees

Practices

• Animal Production: animal protection and health, behavior, pollination services, pesticide impacts

Pesticides are widely used to prevent the loss of crop yields to insect pests. However, pesticides can also have detrimental effects on beneficial insects that contribute to successful crop pollination. While there has been much recent interest in the effects of pesticides on bees, the majority of this research has focused on honeybees (Apis mellifera) and bumblebees (Bombus spp.), with experiments largely conducted under lab conditions. However, other bee species are also critical pollinators to many crops. The majority of the 4,000 bee species in North America are solitary and ground nesting, and in Cucurbita crops (pumpkin, squash, zucchini) the specialist ground nesting squash bee (Eucera pruinosa) provides the majority of the pollination services. Recent studies have shown that insecticide exposure in semi-field experiments can reduce the reproductive success of squash bees, but how pesticide exposure impacts their foraging behavior and ultimately, population numbers, is not known. If foraging behavior or abundance is negatively impacted by exposure this could have major consequences to pumpkin production. In this study I will assess the influence of pesticide exposure on squash bee communities across sites in central Texas. Specifically, I will address how pesticides impact squash bee abundance and if the effects of exposure to two commonly used insecticides (thiamethoxam and bifenthrin) can be predicted based on their toxicity to honeybees. 

Aim 1: Assess how pesticide exposure and landscape composition impact squash bee abundance . It is critical to understand exposure across the community, but especially for the key pollinator, E. pruinosa; this will be done To understand variation in pesticide exposure across sites we will  compare the pesticide residues detected in the bees themselves to the residues detected in the pollen and nectar from the plants, soil, whole bees (squash bees and honeybees), and bee guts (squash bees and honeybees) from each site. Pollinator surveys on cultivated pumpkins were conducted at 17 farms in West Texas three time points during the blooming period. Specifically, we will compare how bee abundance is predicted by a traditional hazard assessment that only considers the concentrations of pesticides in the crop nectar versus a hazard assessment that additionally considers exposure through pollen and soil (Chan et al., 2019). This allows us to identify the most important routes of exposure by comparing these two different hazard assessments to our measures of pesticide residues in individual bees, to see what routes of exposure are most important to consider to prevent population declines.  

Aim 2: Experimentally test if exposure of two commonly used insecticides have lethal or sub-lethal effects on squash bees. The effects of insecticides on pollinators are typically tested using honey bees and bumblebees; we have adapted established protocols from those species to test how field realistic exposure of two commonly used insecticides affects squash bees. Specifically we will address if propensity to forage is negatively impacted by field realistic exposure to thiamethoxam and bifenthrin with a proboscis extension response assay that can be used on wild caught bees. This will allow us to test whether insecticide effects on these responses are generalizable beyond model species.