Leafcutter bees use plants not only as pollen and nectar sources, but also cut leaf discs and use them to line their nests. Which plant species they choose as nesting material and why have remained obscure, however. We explored leaf choices of Megachile spp. from three climatically and ecologically contrasting regions in the world (tropical South Asia, temperate Canada and Southwest US desert). Weasked:1) how are plant species known to be used by leafcutter bees distributed across the angiosperms? 2) does plant choice differ across geographical regions, and if so, what drives this choice? and 3) are the most heavily used plant species in each region natives or exotics? To determine whether leaf selection was predicted by clade, family, local abundance, or the geographical zone of origin of available plant species, we monitored over 3000 plants of 208 native and exotic species planted in the 3 sq. km. campus arboretum of University of Arizona and recorded leaf damage inflicted by bees.
Results/Conclusions
Megachile in all three regions showed a strong preference for plants in the rosid clade (71%-77% of the plants used by the bees), particularly the phylogenetic cluster of Fabales, Fagales and Rosales (together ~45%). Most species from the ancient Magnolid clade were also used. As would be expected, plant species used by leafcutter bees differed greatly among these regions (average similarity=2.8%). However, plant use was similar at the levels of genera (14.73%) and family (43%) across the geographical regions, suggesting that preferences are preserved at the higher taxa or at the root clade level. Membership in the rosid clade and Fabaceae family predicted bees’ plant preferences, whereas the plant species’ local abundance and geographical origin did not. Within a given geographic region, 32-45% of the plants leafcutter bees selected were introduced species. We argue that consideration of leafcutter bees’ plant preferences might help explain the underlying reasons for their cosmopolitan distribution. This information is vital if we aim to manage their habitats in a way that guarantees the persistence of these ecologically critical pollinators.