Native bee pollinator diversity in Oregon blueberries

Pollination is critical for the production of larger, better quality, earlier ripening blueberries. In Oregon, highbush blueberry producers typically stock honey bee hives but honey bees do not perform efficiently during the cool weather conditions that prevail during bloom. Native bees, especially bumble bees, are considered to be better pollinators of blueberries as they forage in colder temperatures, and they remove blueberry pollen efficiently through buzz pollination. The Pacific Northwest has a rich diversity of native bees, but there is little information on their presence in blueberry growing regions during bloom. Our objective was to determine the diversity and abundance of native bees in highbush blueberry fields in Oregon. Weekly surveys were conducted over four weeks of bloom in five blueberry fields in the Willamette Valley in western Oregon. We collected 30 native bee species belonging to five families in 11 genera. Six species of bumble bees were collected, of which Bombus vosnesenskii Radoszkowski was collected in the greatest abundance. Other native bees comprised 79% of the captured bees. In the analysis of variance, the interaction of sites and weeks significantly influenced native bee captures. The five sites differed in production practices, location and adjacent habitats but there was 48% to 66% similarity in total native bees captured based on the modified Sorenson's Coefficient. However, when bumble bees were compared, one site was observed to have a significantly higher abundance compared with the other four sites. No location or production specific factor accounting for the difference was identified. Overall, the study indicated a rich native bee fauna in Oregon during blueberry bloom. However with the projected increases in blueberry production in future years, there is a need to conserve existing populations, and adopt management strategies that encourage build-up of native bee fauna in blueberry fields, and in surrounding landscapes.