Strawberries are among the most important fruit crops in Denmark and are commonly grown in tunnels to enable season long production using ever bearing cultivars. These systems depend heavily on commercial bumblebees (Bombus terrestris) for pollination, especially early in the season when natural pollinators are scarce. Tunnel grown strawberries are affected by arthropod pests and diseases, with Western Flower Thrips (Frankliniella occidentalis) representing a major challenge during flowering. Control options for thrips are limited, and microbial agents such as the ento-mopathogenic fungus Beauveria bassiana are considered alternatives, although their use during flowering raises concerns for pollinator safety.
This study investigated whether commercial bumblebee hives can vector B. bassiana (BotaniGard WP, strain GHA) to strawberry flowers to control thrips, and assessed potential effects on bumblebee health.
Laboratory bioassays showed dose dependent mortality of thrips exposed to B. bassiana. Bumblebees successfully transferred viable fungal spores to flowers in greenhouse experiments, where spores persisted for up to one week. However, api vectoring did not significantly reduce thrips infestations under greenhouse conditions.
Direct laboratory exposure to B. bassiana was lethal to individual bumblebee workers, but colony level exposure in greenhouse settings showed no detectable effects over two weeks. Api vectoring resulted in fungal accumulation within hives and changes in gut microbiota, without observable impacts on mortality, activity, or colony growth. The results demonstrate that api vectoring of B. bassiana to strawberry flowers is feasible, but improved environmental conditions and longer term studies are needed to evaluate practical efficacy and pollinator safety under commercial production.