Pollen use by osmia lignaria (Hymenoptera: Megachilidae) in Highbush blueberry fields

Abstract

The blue orchard bee, Osmia lignaria (Say) (Hymenoptera: Megachilidae), is an alternative managed pollinator of rosaceous tree-crops, and potentially could be used for blueberry (Ericaceae) pollination. However, the floral preferences of this species for other types of flowers could prevent them from visiting blueberry flowers when alternative forage is available. To evaluate O. lignaria suitability for pollination of commercial blueberries in Michigan, we identified the main pollen sources in scopal loads and brood provisions, and determined the contribution of blueberry pollen to pollen collected by females nesting inside or at the border of a large blueberry field. Across two bloom seasons, we found that blueberry pollen was not the most abundant pollen type in either the scopal loads (â ‰6%) or the brood provisions (13-20%). Black cherry (Prunus serotina, Rosaceae), white clover (Trifolium repens, Fabaceae), and red clover (Trifolium pratese, Fabaceae) were the most abundant pollen types in the brood provisions. While shelter location (inside or at the border of the field) had an influence on the use of some of these plants, it did not affect the use of blueberry pollen. Our results indicate that in these field conditions, O. lignaria visit other plants rather than blueberries as a pollen source, making it poorly suited as an alternative managed pollinator for this specific crop.