Effectiveness of Bumblebees and Honeybees for Delivering Inoculum ofGliocladium roseumto Raspberry Flowers to ControlBotrytis cinerea

The effectiveness of bees in vectoring inoculum of the biocontrol agentGliocladium roseumto raspberry flowers was investigated in shade-cloth-enclosed field plots of raspberry cv. Boyne and cv. Redwing. For bee-vectoring treatments, a colony box of bumblebees with about 50 workers, or a hive of honeybees with about 3000 workers, was placed in each replicate plot enclosure. Each colony box and hive was equipped with an inoculum dispenser to contaminate bees with a powder preparation ofG. roseum(4.0–18.0 × 108CFU/g). Bumblebees carried inoculum loads of 0.3–128 (x = 39.7) × 104CFU/bee and honeybees carried 1.3–81 (x = 29.9) × 104CFU/bee when they emerged from dispensers. Similar amounts of inoculum were delivered to raspberry flowers by bumblebees (mean daily density of 451–2461 CFU/flower) and honey bees (693–1659 CFU/flower). Bees maintained inoculum densities of ≥ 102–103CFU/flower during 6- to 15-day study periods except when weather discouraged foraging. Inoculum density on flowers in plots that were sprayed withG. roseum(107CFU/ml) decreased from about 102–105to < 10 CFU/flower within 2 days. Inoculum density on individual flowers varied (from 0–20,666, 0–4000, and 0–44,166 CFU/flower, respectively) in plots treated with bumblebees, honeybees, or sprays. Incidence of flowers with no inoculum was high in sprayed plots (55–57%) compared to plots treated by bumblebees (6–9%) or honeybees (14–15%).G. roseumgenerally suppressedB. cinereain stamens and stigmas more effectively when applied by bees than as a spray. All treatments moderately suppressed fruit rot in cv. Boyne but not in cv. Redwing. A combination of bee-vectoredG. roseumto protect flowers and a spray against direct infection of fruits is proposed to optimize fruit rot control.