Wild bees nest in the stems of cultivated Rubus plants and act as effective crop pollinators

In order to act as effective agricultural pollinators wild bees must not only pollinate the target crop, but also have nesting behaviours that allow them to nest nearby or in situ. To establish their potential as crop pollinators we studied stem-nesting bees in the genus Exoneura, in and around Rubus berry farms in the Yarra Valley, Australia, where they had been observed nesting in nearby forested areas. Honey bees (Apis mellifera L.) are used as managed pollinators of Rubus crops, but we found that a single Exoneura visit to blackberry (Rubus fruticosus L. sp. agg.) was equivalent to a single honey bee visit, causing a three-fold increase in drupelet count. We found Exoneura nesting on farm in the stems of raspberry (Rubus idaeus L.) plants, at an estimated density of 3320 bees per hectare. Nests were more likely to be found in stems that were narrow and upright, suggesting that crop pruning strategies could focus on preserving select suitable stems for nesting. Exoneura were more abundant on flowers when local nest density was high (at 50 m) and when there was more native vegetation cover nearby (1 km), indicating that Exoneura are flexible in their selection of nesting habitat and able to nest on farm, but with their broader-scaled abundance still influenced by presence of native vegetation.