High pesticide exposure and risk to bees in pollinator plantings adjacent to conventionally managed blueberry fields.

Authors: Graham, Kelsey; MCART, SCOTT - Cornell University; ISAACS, RUFUS - Michigan State University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pollinator plantings are installed adjacent to agricultural crop fields to provide benefits such as increased diversity and abundance of wild bees. They provide benefits to bees including increased diversity of floral resources, and nesting resources. However, their proximity to pest management in the crop field may make them vulnerable to pesticide drift. Here, we tested flower and soil samples taken from pollinator plantings, unenhanced field margins, and within the crop field (blueberries) and measured them for pesticides. Additionally, we placed bumble bee colonies (Bombus impatiens) on farms and measured pesticides in bee-collected pollen. We found that pesticide exposure and risk was equivalent between farms with and without pollinator plantings, indicating that presence of pollinator plantings does not reduce pesticide exposure for wild bees. Additionally, pesticide risk was considered very high in flower samples and in pollen samples, indicating that floral resources on farms (in pollinator plantings or flowering weeds) may represent significant pesticide exposure routes for bees during the summer (post-crop bloom). Management strategies to reduce pesticide exposure at flowers on blueberry farms should be undertaken.

Technical Abstract: Wildflower plantings adjacent to agricultural fields provide diverse floral resources and nesting sites for wild bees, and so they are recommended for supporting pollinators on farms. However, their proximity to pest control activities in the crop may result in pesticide exposure and risk if pesticides drift into plantings and are contacted by wild bees. To quantify pesticide residues in pollinator plantings, we sampled flowers and soil in areas adjacent to blueberry fields with wildflower plantings or typical mowed grass perimeters, and compared them to samples from crop row middles. Flower samples at conventionally managed farms with or without pollinator plantings had similar exposure profiles, with high and similar RQ values (with planting RQ: 3.85 ± 3.20; without planting RQ: 4.03 ± 2.73), and no significant difference between sample field locations (crop row middle or field margin). Unsprayed sites had significantly lower risk (RQ: 0.005 ± 0.002). Soil samples had overall low risk to bees, though samples taken from crop row middles were significantly higher in risk compared to those taken from field margins. Additionally, we placed managed bumble bee colonies (Bombus impatiens) in field margins of crop fields with and without plantings and measured residues in bee-collected pollen. Pesticide exposure was similar in bumble bee collected pollen from sites with or without pollinator plantings, and risk was generally high (with planting RQ: 0.49 ± 0.16; without planting RQ: 1.05 ± 0.36). Risk was lower at sites where there was no pesticide activity (RQ: 0.25 ± 0.13), but there was no significant difference between management types. This supports previous findings that bees forage outside the field where they are located and risky exposures can occur in the surrounding landscape, including conventionally managed blueberry farms. Additionally, analysis of pollen collected by bumble bees found agricultural weeds and woody plants commonly found in wooded areas surrounding fields in this region with no significant difference in floral species richness between sites with and without pollinator plantings. These data, including elevated risk associated with flower and pollen samples at sites with and without pollinator plantings, suggest that plantings do not reduce pesticide risk and do not increase the pollen diversity collected by B. impatiens, within the contexts of this study. Our results highlight the need to reduce exposure, including enhanced IPM adoption, drift mitigation, and removal of attractive flowering weeds prior to insecticide applications. The costs and benefits of installing pollinator plantings should also be closely considered given the findings of this study that suggest they can be major routes of pesticide exposure for wild bees.