Pesticide risk to managed bees during blueberry pollination is primarily driven by off-farm exposures

Authors: Graham, Kelsey; MILBRATH, MEGHAN - Michigan State University; ZHANG, YAJUN - Michigan State University; BAERT, NICOLAS - Cornell University; MCART, SCOTT - Cornell University; ISAACS, RUFUS - Michigan State University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2022
Publication Date: 5/3/2022
Citation: Graham, K.K., Milbrath, M.O., Zhang, Y., Baert, N., McArt, S., Isaacs, R. 2022. Pesticide risk to managed bees during blueberry pollination is primarily driven by off-farm exposures. Scientific Reports. 12. Article 7189. https://doi.org/10.1038/s41598-022-11156-1.
DOI: https://doi.org/10.1038/s41598-022-11156-1

Interpretive Summary: Managed bees are crucial for crop pollination. However, bees can be exposed to pesticide residues while on farms for pollination. Therefore, understanding typical exposure and the hazards associated with this exposure is critical for developing management strategies for reducing risks to bees. Honey bees and bumble bees are both used for highbush blueberry pollination. We performed pesticide residue analysis on blueberry flowers, foraging honey bees and bumble bees, honey bee and bumble bee collected pollen, and wax from honey bee hives while colonies were placed in blooming blueberry farms in southwest Michigan. We then calculated the associated hazard of these pesticide detections based on toxicity data. Pesticides in pollen were generally more hazardous compared to pesticides in the other sample types, and most pollen samples were above a hazard threshold of concern. The most common causes of high sample hazards were pesticides not sprayed on blueberry farms during bloom. Therefore, the most hazardous exposures to bees are happening off the farm where they are located. Management strategies to reduce hazards to bees should therefore be implemented across the diverse agricultural landscape, not just on the farms where bees are located.

Technical Abstract: When managed bee colonies are brought to farms for crop pollination they can be exposed to pesticide residues. Quantifying the hazard posed by these exposures can indicate which pesticides are of the greatest concern and helps focus efforts to reduce exposure. To estimate the hazard from pesticides to bees while they are pollinating blueberry fields we sampled blueberry flowers, foraging bees, pollen collected by returning honey bee and bumble bee foragers at colonies, and wax from honey bee hives in blooming blueberry farms in southwest Michigan. We screened the samples for 259 active ingredients using a modified QuEChERS method. The most abundant pesticides were those applied by blueberry growers during blueberry bloom (e.g. fenbuconazole and methoxyfenozide). However, we also detected highly toxic pesticides not used in this crop including chlorpyrifos, clothianidin, avermectin, and thiamethoxam. Using LD50 values for contact and oral exposure to honey bees, we calculated the Hazard Quotient for each individual pesticide and the average sample HQ for each farm. Pollen samples were the most likely to have detections above the HQ threshold of concern compared to the other sample types (48.5% of honey bee pollen samples; 66.7% of bumble bee pollen samples; 2.5% of flower samples; 10.3% of whole honey bee samples; 0% of whole bumble bee samples; 12.4% of wax samples). Average sample hazards varied widely by farm, with most farms having average HQ values above the relevant threshold of concern, and some farms with samples above the elevated threshold. There was also considerable variation in hazard between the two sampled years. Landscape analysis indicated that high sample hazards were correlated with the abundance of other crops located within the flight range of the bees. Our results highlight the need to mitigate pesticide hazards to bees across the wider agricultural landscape, in addition to focusing on the impact of applications on the farm where they are applied.