Efficacy of Bumble Bee Disseminated Biological Control Agents for Control of Botrytis Blossom Blight of Rabbiteye Blueberry

Abstract

Botrytis blossom blight caused by Botrytis cinerea may cause severe crop loss in rabbiteye blueberry, necessitating applications of expensive fungicides. Commercial bumble bees, Bombus impatiens, were tested as vectors of the fungicidal biological control agents, Prestop® (Gliocladium catenulatum) and Mycostop® (Streptomyces griseoviridis), against blueberry blossom blight. A single bumble bee hive and four flowering blueberry plants were confined within each of ten 1.5-m3 insect exclusion cages. Test products were applied onto the bodies of worker bees exiting each hive through a tubular V-shaped dispenser containing the test product affixed to the hive's entrance. Dissected floral parts were plated onto agar and recovery frequency of biological control agents was determined. Stylar infection rates were 100% for S. griseoviridis and 70% for G. catenulatum. In field trials, bumble bees vectored a UV-fluorescent dye and biological control agents to about one-third of the open blueberry flower clusters in a small field in as few as 8 days. Flowers were inoculated with B. cinerea 10 days after placing biological control agent vectoring bee hives in the field. The inoculated flowers on bee-visited stems (Prestop treated flowers) had more white corollas (71%) and a lower disease incidence than unvisited flowers (52% white corollas). These results indicate that bumble bees can vector sufficient biological control agent to blueberry flowers to reduce floral damage caused by B. cinerea, however, disease control may not have sufficient economic impact under high disease pressure.