Bombus terrestris as biocontrol agent vector to suppress Botrytis cinerea in greenhouse tomato.

BACKGROUND Tomato gray mold, caused by Botrytis cinerea, is a major disease affecting tomato yield and quality. Excessive use of chemical fungicides has led to resistant strains. Due to the drawbacks of chemical fungicides and traditional spraying, entomovectoring methods have been developed for plant protection. Here, the potential of a biocontrol agent vectored by Bombus terrestris using a self-made flying doctor system to inhibit gray mold on tomato plants during flowering was investigated. RESULTS A 14-day risk assessment and a 4-week chronic toxicity study demonstrated that Trichoderma harzianum and Bacillus subtilis had no negative effects on bumblebee performance or activity. Bacillus subtilis exhibited superior antipathogen efficacy on plates and detached fruit at the same fold recommended field concentration (RFC). Consequently, it was selected for field trails, which revealed that the Bacillus subtilis could be carried by Bombus terrestris via a self-made dispenser and delivered to flowers at an average of 102 to 103 colony-forming unit (CFU) per flower. The Bacillus subtilis-vectored group reduced Botrytis cinerea infection rates by an average of 54.2% compared to the control group. Furthermore, its effectiveness was comparable to traditional spraying methods, with no significant difference in infection rates between the two approaches. CONCLUSION This study demonstrated that Bacillus subtilis vectored by Bombus terrestris through a self-made dispenser during flowering successfully decreased Botrytis cinerea infection without adversely impacting on bees, achieving a level of disease prevention comparable to traditional spraying methods. These findings provide a foundation for efficient and sustainable management of gray mold in greenhouse tomatoes. © 2025 Society of Chemical Industry.