The synergistic effects of stressors on bee mortality

The global declines in bee populations threaten food security and wild ecosystems. Declines are thought to be driven by interaction effects between agrochemicals, parasites and nutritional stressors. However, studies investigating these interactions have produced varied results. Here Harry Siviter and colleagues carry out a meta-analysis of the interaction effects between agrochemicals, parasites and nutritional stressors on the health of bees. Synergistic effects, whereby the impact of combined stressors is significantly higher than predicted additive effects, on mortality occur when bees are exposed to multiple agrochemicals at field-realistic levels. Interactions are not greater than additive expectations when bees are exposed to parasites and/or nutritional stressors. Environmental risk assessment schemes that assume additive effects of agrochemical exposure may underestimate the impact of anthropogenic stressors on bee mortality.