Potential of bumble bees as bio-vectors of Clonostachys rosea for Botrytis blight management in lowbush blueberry

The effectiveness of bees as vectors for microbial biological control agents has been demonstrated in greenhouses and some small-acreage crops. Less is known about the viability of this tactic for other cropping systems, or the effects of outfitting hives with dispensers on the bees. Experiments conducted in lowbush blueberry (Vaccinium angustifolium) fields indicated that home-made wooden, Koppert, and Enviroquest dispensers had no significant effects on foraging behavior or pollen loads of the bumble bee Bombus impatiens, but the presence of a dispenser did reduce the rate of workers exiting hives. Following exit of bees from dispensers, no difference was found in the quantity of the microbial agent Clonostachys rosea applied to the bees or blossoms, and distribution of product in the field was not influenced by dispenser design or distance from hives. However, the prevalence of the pathogen Botrytis cinerea in blossoms from cages that contained hives with dispensers with C. rosea was significantly less (10-20 %) than blossom infection in control plots, despite unseasonably inclement conditions and restricted foraging. These results suggest that C. rosea can be effectively delivered by commercial bumble bees for prevention of B. cinerea infection in V. angustifolium, but the efficacy of the technique will be limited during periods of poor weather that often occur in regions where lowbush blueberries are grown. Some technical issues with dispensers and commercial B. impatiens hives also need to be addressed before widespread use can be expected within commercial lowbush blueberry production.