Floral strips adjacent to rotationally managed crop fields significantly increase nesting density and support pollen foraging of leafcutter bees

1. Bees in many regions of the world are in decline with strong evidence that agricultural practices are to blame. Although wildflower enhancements adjacent to croplands have proven effective at increasing wild bee abundance and diversity, how these enhancements can improve the diet and nesting density of bees remains poorly known. 2. We placed hollow reeds next to floral strips, control fields, and semi-natural areas in Manitoba from 2019–2021 to determine how pollen utilization and provisioning density of stem-nesting leafcutter bees ( Megachile ) differed between treatments. 3. We found that strip sites significantly increased nesting density of Megachile when compared to the other treatments. Strip sites contained the most pollen species, including 30 % of species sown into the floral strip itself, suggesting that Megachile use the strip for pollen provisioning. 4. At the landscape scale, nesting density of Megachile responded positively to the amount of rewarding agriculture (crops frequently visited by insects for floral rewards). However, the number of offspring per nest responded negatively to rewarding agriculture and local Shannon vegetation diversity, indicating that Megachile create more nests with fewer offspring in areas of large-scale flowering crops or higher vegetation diversity. Possible reasons for this are discussed. 5. Our research supports the idea that floral strips increase beneficial insect abundance and that floral strips supplement pollen foraging of bees. • Floral strips increase nesting rates of Megachile over control or natural treatments. • Strips provide up to 30 % of pollen used for Megachile offspring provisioning. • Nesting density responded positively with blooming agriculture within 3 kilometers. • Number of offspring per nest was negatively associated with local vegetation diversity.