Using Commercial Bumble Bee Colonies as Backup Pollinators for Honey Bees to Produce Cucumbers and Watermelons

Abstract

The effectiveness of bumble bees, Bombus impatiens Cresson, and honey bees, Apis mellifera L., on the pollination of cucumber, Cucumis sativus L., and watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai, was compared under field conditions. Comparisons were based on fruit abortion rates and seed set as influenced by bee type (honey bee or bumble bee) and the number of bee visits to treatment flowers (1, 6, 12, and 18 bee visits), plus two controls: a no-visit treatment and an open-pollinated (unrestricted visitation) treatment. For both crops, an increased number of bee visits had a strong positive effect on fruit and seed set. All cucumber and watermelon flowers bagged to prevent insect visitation aborted, demonstrating the need for active transfer of pollen between staminate and pistillate flowers. Bumble bee-visited flowers consistently had lower abortion rates and higher seed sets in the cucumber and watermelon studies than did honey bee-visited flowers when compared at the same bee visitation level. Only slight differences in fruit abortion rates were detected between bee types in the watermelon study. However, abortion rates for bumble bee-visited flowers were consistently less than those for honey bee-visited flowers when compared at equal bee visitation levels, with one exception at the 12 bee visit level. As the number of honey bee colonies continues to decline due to parasitic mite pests and based on the data obtained, we conclude that bumble bees have a great potential to serve as a supplemental pollinator for cucumbers, watermelons, and possibly other vine crops, when honey bees available for rental are in limited supply.