Influence of agricultural intensification on pollinator pesticide exposure, food acquisition and diversity

Pollinators are essential for maintaining sustainable crop production, while the decline of pollinators is a widespread concern. Agricultural intensification is one of the primary drivers of the decline of insect pollinators. Agricultural intensification usually involves a decreasing of non-crop semi-natural habitat and an increasing of pesticide exposure for pollinators. However, causal links between agricultural intensification, increased pesticide exposure, and reduced pollinator's food sources and pollinator diversity remain underexplored. We assessed pollinator diversity across a landscape gradient where the proportion of rice ranged from 11% to 85% in South China. We placed honeybee (Apis mellifera) and mason bee (Osmia excavata) in these landscapes and investigated pesticide exposure in honeybee foragers and pollen, and in mason bee pollen and nesting materials. We also assessed the acquisition of food by mason bees. We found a higher frequency of pesticide detection in honeybee foragers and honeybee pollen samples in areas with a higher proportion of rice fields. There was a strong positive relationship between mason bee food acquisition and the proportion of semi-natural habitats, while no significant effects of pesticide exposure on pollinator diversity were found in addition to the effect of semi-natural habitat. Synthesis and applications: Our results suggest that pollinator communities could be at an increased risk of pesticide exposure due to intensified agriculture, while the negative impact on pollinator diversity mainly results from the loss of habitat and/or reduced food sources. This study highlights the importance of conserving semi-natural habitat to mitigate the causes of decline in pollinator diversity. We also recommend long-term, multi-year studies to further understand the mechanisms behind the loss of pollinators in farming landscapes.