Use of nest and pollen resources by leafcutter bees, genus Megachile (Hymenoptera: Megachilidae) in Central Michigan

Abstract

Many landscapes throughout the Great Lakes region have experienced reductions in floral and nesting resources for bees. Identifying the resources used by bees in the family Megachilidae can be used to inform conservation programs that aim to support this group. In this study, we identified the preferred nesting substrate and size, as well as the proportion of distinct pollen types used for offspring provisioning by Megachile (Hymenoptera: Megachilidae) species. A total of 39 completed artificial nesting tubes were collected between July 25 and August 30, 2016. A majority of completed nests were in 4 mm diameter tubes. However, more 6 mm and 7 mm diameter nests were occupied later in the season. A total of 98 cells from 20 nests were analyzed for the composition of the pollen provisions. Nesting females gathered pollen primarily from Trifolium repens L.-type (70.2% of total pollen) and the majority of collection of this species occurred between July 25 and August 10. There was also frequent pollen collection from Centaurea stoebe (L.) (9.0%), Rudbeckia-type (8.4%), and Cirsium spp. (8.3%) with the majority of collection from these species occurring after August 10. Our results show that Megachile species at our mid-Michigan site exhibited strong preferences for specific nest hole sizes, and they primarily collected pollen from non-native plants. This information can inform efforts to build local populations of these summer-active bees using combined nesting and foraging resources.