Can bumblebee (Bombus impatiens) queens avoid pesticide-contaminated soils when selecting underground hibernation sites?

New evidence points to substantial impacts of exposure to pesticide residues in soil for a range of bee taxa that have close regular contact with this substrate. Among others, the exposure risk is high for bumblebee (Bombus spp.) queens hibernating in agricultural soils. An important question is whether bees can detect and avoid pesticide-contaminated soils, or whether they might be attracted to such residues. To address this question, we performed a multiple-choice preference experiment in which newly emerged Bombus impatiens queens were given access to multiple crates of soil treated with different pesticides in large enclosures in fall 2021. Five of the most commonly encountered pesticides in agricultural soils (boscalid, chlorantraniliprole, clothianidin, cyantraniliprole, difenoconazole) were selected for testing at two contamination levels (lower or higher; 4 enclosures/level), based on field-realistic exposure estimates. Queen-producing bumblebee colonies (4/enclosure) were allowed to fly freely in enclosures for five weeks. We then compared the proportion of hibernating queens found in each soil type. Bumblebee queens (n=173) consistently avoided pesticide-free soil at both contamination levels (p=0.01), while showing no avoidance for any pesticide-treated soil types. On average, queens selected the pesticide-free soil 1.3-2.4-fold less frequently than any of the spiked soils at the lower contamination level, and none of the queens from the higher contamination enclosures selected pesticide-free soil. This apparent preference for pesticide-contaminated soils increases the likelihood of exposure to and potential hazard from pesticide residues in soil for bumblebee queens during hibernation, a critical and highly vulnerable period of their annual life cycle.