Blue orchard bees improve pollination of spring fruit crops

Efficient pollination of tree fruit crops is a necessary component of orchard management. The supply of honey bees for pollination of tree fruit orchards has become increasingly limited and expensive due to various pest, disease, and environmental factors. However, Osmia lignaria (blue orchard bee) can be managed as highly-efficient pollinators or co-pollinators of early spring crops due to their behavior and life history. O. lignaria is a spring-flying, cavity-nesting bee that forages in cool temperatures, which makes them well-suited for early-blooming and high elevation orchards. Over three years, we measured pollination of Washington State pear and sweet cherry crops in two treatments: 1) the combination of O. lignaria and honey bees, and 2) only honey bees. Honey bees were stocked at the standard stocking density for cherry and pears in both treatments. We assessed fruit set and fruit yield for both crops. We found that in all trials, the addition of O. lignaria for both cherry and pear crops increased fruit set. This increase in fruit set, however, did not translate to an increase in fruit yield. Given the increasing demand for honey bees (e.g., for almond pollination) and the challenge of keeping bee colonies healthy and affordable, it is important to identify alternative pollinators that may be better suited for early spring fruit crops.