Climatic change alters effects of pesticides on wild bees and pest control in oilseed rape

Pollinators provide valuable ecosystem services to agricultural landscapes; however, they are threatened by several factors of decline. Particularly for wild pollinator species, the effects of stressors neither individually nor in interaction with each other are well understood. Pesticide use is known to impart various lethal and sublethal effects on pollinator populations, and this use is likely to undergo modification with climatic change due to variation in environmental conditions and pest pressure. In order to inform management and policy decisions regarding pesticide use and pollinator conservation in agriculture in the coming decades, the interactive effects of pesticide exposure and climatic change on pollinators require examination. This study aimed to quantify these interactive effects for the pollination system of oilseed rape in Sweden, where this mass-flowering crop is widely grown. The effects of this interaction, simulated by increased winter temperature and the application of three pesticides at two concentration levels, were explored in three areas that represented the research objectives: a) pest infestation of oilseed rape, b) individual- and colony-level bumblebee (Bombus terrestris) pollination behavior and health, and c) oilseed rape yield. To address these objectives, data from a large-scale field experiment were analyzed with generalized mixed effects models to compare the effects of different pesticide-climate treatments. The findings suggest that pesticide effectiveness against pests will be diminished under climatic change and that individual- and colony-level foraging by bumblebees will remain unaffected or become less affected by field-realistic pesticide exposure with climate warming. However, interactive effects on bee locomotor activity were present and diverged according to the type of pesticide. Yield quantity was not affected by pesticide, climate warming, or their combination. It is recommended that farmers and policymakers enact integrated pest and pollinator management (IPPM) strategies to prevent increases in pesticide use and to balance the benefits of pollination services and pest control under climatic change.