Diversification mitigates pesticide but not microplastic effects on bees without compromising rapeseed yield in China

Humanity depends on agriculture for food, fiber and energy provisioning, but input-intensive agricultural production is impacting ecosystem services such as pollination. Pollution effects from neonicotinoid insecticides on pollinators receive much attention, but nothing is known on the synergistic effects with emerging plastic contaminants and the mitigation potential of agricultural diversification. Here, we conduct the first large-scale and full-factorial mesocosm study to understand two-generation effects of diversified floral resources (diversification treatment), neonicotinoid and microplastic pollution (pollution treatments) on Osmia cornifrons bees in 72 mesocosms. In our three-year experiment, we found that diversification can mitigate individual neonicotinoid effects. We did not find any individual or synergistic effects of microplastic on reproductive performance of solitary bees. None of our treatments affected rapeseed yield. Our results confirm the benefits of diversified flower resources to mitigate pesticide effects on bees in China and suggest that microplastics have no acute individual or interaction toxicity in semi-natural environment at realistic exposure levels. Diversified flower resources in Chinese agricultural landscapes to mitigate pesticide pollution effects on pollinators is an important policy argument for pollinator protection with downstream implications for food security.