Tall trees and exotic herbs identified in pollen and nest materials of seven cavity-nesting solitary bee species in Australia

Introduction Solitary bees are important pollinators yet vulnerable to decline in resource-poor landscapes. Resources for solitary bees may be supplemented by land managers through targeted plantings, however, little is known about the specific plants used by different species. This study identified plants used by seven cavity-nesting solitary bee species in natural and agricultural landscapes over two years by DNA metabarcoding of pollen bread, larvae, frass and nest materials. Methods We sequenced samples from the bee species: Megachile mystacaena (23 nests), Megachile mackayensis (2), Megachile simplex (11), Megachile deanii (3), Hylaeus ruficeps (1), Hylaeus nubilosus (6) and Hyleoides concinna (3). We identified 118 plant taxa from brood provisions (or larvae and frass proxies) and nest materials, however, just 20 taxa accounted for more than 70% of all resources used. Importantly, trees were the most frequently provisioned pollen source for all bees (48 taxa). Results Introduced plants were used by all bee species studied, even in natural landscapes. Native plants, however, still accounted for more than 50% of relative read abundance for six of seven bee species. Plants identified in nest materials were mostly herbaceous species for leafcutter bees, vines and trees for cellophane bees and parasitic plants (Santalales, “mistletoes”) for resin bees. Discussion Agri-environment schemes to support pollinators may be benefit from the inclusion of these taxa or plants with similar characteristics, particularly flowering trees.