2017 ASHS Annual Conference

Fruit set in northern highbush blueberry (Vaccinium corymbosum) is relatively low, especially in western Washington. Climactic conditions influence the activity levels of blueberry’s primary commercial pollinator, the honey bee (Apis mellifera). Cool springs with frequent rainfall, which is common in western Washington, can reduce honey bee activity, pollination efficiency, and subsequent fruit set and yields. Increasing honey bee density may increase fruit set, even during bloom periods with unfavorable weather for honey bee activity. Additionally, colonies of native bumble bees (Bombus sp.) are becoming increasingly commercially available and their use may improve pollination in regions with low honey bee activity. The objective of this study was to evaluate if modified honey bee hive densities and supplementation with native bumble bees improves pollination and subsequent yield components in western Washington blueberry. To address this objective, two experiments were conducted in commercial ‘Duke’ and ‘Draper’ plantings in 2016. For the hive density experiment (Experiment 1), three ‘Duke’ sites were stocked with 2 hives/ha of honey bees (control) and another three sites were stocked with 4 hives/ha. For the bumble bee supplementation experiment (Experiment 2), three ‘Draper’ sites were stocked with 2 hives/ha (control) and another three sites with 2 hives/ha plus 3 colonies of bumble bees (Bombus vosnesenskii). Honey bee activity, yield components, and fruit quality attributes (berry firmness and weight) were monitored. There were no significant differences in fruit set or estimated yield regardless of increased honey bee density or bumble bee supplementation in 2016. However, a consistent numerical trend of increasing fruit set and yields with increased honey bee hive density was observed. Seed number per berry and berry weight were significantly increased with increased honey bee density. Results indicate that increasing honey bee hive densities can help blueberry growers overcome reduced fruit set due to insufficient pollination.