Supplementing small farms with native mason bees increases strawberry size and growth rate.
Pollination services, especially those of bees, play a vital role in agriculture. Declining honeybee populations require us to find alternative solutions for sustainable agriculture. Native bees are proving to be efficient pollinators. Mason bees (Osmia lignaria) provide valuable pollinator services for some woody orchard species, but their value as pollinators for herbaceous crops is largely untested. We assessed the effectiveness of O. lignaria supplementation on nine strawberry farms over two growing seasons. We specifically selected mason bees for this work because they emerge from cocoons in the springtime, when few other bees are available for pollination. Cocoons are easily deployed on farms and emerged bees have a small flight radius, so they remain localized. We placed cocoons on one side of each berry farm plot (our mason bee addition treatment) but not on the opposite side (our control). We tagged and monitored berries on nine farms throughout the growing season. We performed statistical comparisons of berries from the treatment and control for differences in berry growth rate and size. In addition, we supplemented farms with native bee homes constructed from three materials (bamboo, Phragmites and wood). This allowed us to determine whether adult mason bees would produce a subsequent generation of bees on farms and whether the bees had a preference for nest material type. Our work demonstrates that mason bees can be used successfully to pollinate herbaceous berry crops. We found that berry growth rate was significantly higher and berry volume was significantly larger for berries from the treatment relative to the control. We also found that adult bees successfully utilized the bee homes for laying the next generation of offspring and that bees colonized bamboo homes more than other home types. Synthesis and applications. Our results are the first to show that native mason bees (Osmia lignaria) can be used successfully to provide pollination services on strawberry farms. Their use results in the production of bigger berries and faster berry growth rates than managed honeybees alone. Mason bees overwinter (and can be purchased) in cocoons, offering great potential for efficient and effective pollination services, for a variety of agricultural applications across different geographical regions. The availability of suitable nesting sites and protection of subsequent generations of cocoons from wasp parasitization warrant future consideration.