Functional leaf and plant use by leafcutter bees: Implications for management and conservation.

Wild solitary bees face a host of challenges from the simplification of landscapes and biodiversity loss to invasive species and urbanization. Pollinator researchers and restoration workers thus far gave much attention to increase flower cover to reduce the impact of these anthropogenic pressures. Over 30% of bee species need nonfloral resources such as leaves and resin for their survival and reproduction. However, the importance of leaves in bee ecology, particularly for leafcutter bees, has received very little attention. Leafcutter bees have global distribution and cut leaves for constructing brood chambers. We have very little information for (a) what bees use and do not use for foraging leaves and (b) what leaf and plant traits and plant community traits drive plant preference and plant usage. To fill this gap and recommend plants for leafcutter bee conservation, we examined 13,062 plants of 612 species and 107 families distributed in 165 plant communities of nine towns/cities of four south Indian states. The plant community of nine locations and four states was quite dissimilar, but had similar proportion of native and exotic plants. The probability of a plant foraged for leaf is governed by its clade, family, nativity, and leaf dimension, particularly the leaf width. Bees have a clear preference for plants of common families, such as Fabaceae, Phyllanthaceae, and Meliaceae for foraging leaves, but bees going to plants of distant lineages, including rare species and families is not rare. At the same time, bees also avoided plants of several cosmopolitan families, such as Apocynaceae, Moraceae, Sapotaceae, and Asteraceae, among others. Bees preferred exotic plants more to native plants. The plant usage in communities is predicted by species richness, proportion of Fabaceae plants in communities, and proportion of herbs; plant diversity and abundance are not crucial drivers. Our study suggests that the bees' preference for leaf-foraging plants is not random, but governed by leaf, plant, and plant community traits. The preference for exotic plants is helpful for planning urban and homestead greening projects as they are dominated by exotics.