On-farm pollinator refuges generte opposing reproductive outcomes for two polylectic bee species.

Pollinator refuges are planted to enhance floral and nesting resources for pollinators, thereby increasing pollinator populations on farms. There is ample evidence refuges can increase pollinator abundance, but it is unclear whether increases result purely from attraction and aggregation or enhanced pollinator reproduction as well. Additionally, recent studies suggest solitary bees might not benefit from on-farm wildflower plantings as readily as bumble bees. To examine the impacts of pollinator refuges on different types of bees, we placed commercially available Bombus impatiens and Megachile rotundata out on 20 Mid-Atlantic farms in 2018, including 10 with established pollinator refuges. Bombus impatiens colonies were placed at farms in spring and summer, repeatedly weighed, collected after ca. 10 weeks, and contents inventoried. We calculated colony growth by subtracting initial weight from maximum weight measured, and MQ indices (males + 3*gynes) to quantify reproductive performance. We also placed 100 M. rotundata cocoons out at farms in spring and collected new cocoons throughout summer and fall. We collected emergent adult offspring, recording female weight and sex ratios to quantify reproductive potential. Analyses suggest M. rotundata female offspring weighed more while B. impatiens colonies grew less on farms with pollinator refuges. Thus, pollinator refuges can enhance reproduction in some species but predicting which species are likely to benefit or not and why will require more research.