Floral resource diversification promotes solitary bee reproduction and may offset insecticide effects – evidence from a semi‐field experiment

Abstract Pollinator declines in agricultural landscapes are driven by multiple stressors, but potential interactions of these remain poorly studied. Using a highly replicated semi‐field study with 56 mesocosms of varying wild plant diversity (2–16 species) and oilseed rape treated with a neonicotinoid, we tested the interacting effects of resource diversity and insecticides on reproduction of a solitary wild bee. Compared to mesocosms with oilseed rape monocultures, availability of resources from wild plants complementing oilseed rape doubled brood cell production. In addition, bee reproduction increased due to plant diversity and identity effects. Exposure to neonicotinoid‐treated oilseed rape reduced bee larval to adult development by 69%, but only in mesocosms with oilseed rape monocultures. Availability of complementary flower resources can thus offset negative effects of neonicotinoid‐treated oilseed rape on wild bee reproduction. Policy should encourage the implementation of diverse floral resources mitigating negative effects of crop monocultures and insecticides, thereby sustaining solitary bee populations in agricultural landscapes.

Pollinator declines in agricultural landscapes are driven by multiple stressors, but potential interactions of these remain poorly studied. Using a semi‐field study, we tested the interacting effects of resource diversity and insecticides on solitary bee reproduction, which increased with wild flowers complementing oilseed rape and was driven by plant diversity and identity effects. Neonicotinoid exposure negatively affected bee reproduction only in oilseed rape monocultures suggesting that complementary floral resources can mitigate insecticide effects. Policy should therefore encourage the implementation of diverse floral resources to sustain solitary bee populations in agricultural landscapes. image