D3387: A path to sanitation: Controlling Bacillus thuringiensis in a lepidopteran mass rearing system

Bacillus thuringiensis (Bt) is a bacterium known for its capabilities as a natural biopesticide against insect pests. However, when mass-rearing insects for biological control (or sterile insect technique), Bt is detrimental and can have catastrophic consequences, potentially crashing the whole insect colony. If not properly controlled, this pathogen rapidly becomes prevalent and difficult to eliminate. Bt forms spores that are highly resistant to disinfectants which makes effective control challenging. Here, we present our efforts and tests conducted in a lepidopteran mass rearing system to manage Bt against navel orangeworm, Amyelois transitella. A quaternary ammonium disinfectant (Quorum) and an autoclave (Steris Amsco Eagle 3041) were tested to sterilize mass rearing containers. Counts of colony forming units (CFUs), prevalence of infected larvae, and adult moth yield were observed. The abundance of Bt CFUs increased for Quorum (+ 150.34%) whereas it decreased when using the autoclave (- 99.35%). The mean severe Bt-infected larvae was 38.57% when treated with Quorum and produced a 56.21% moth yield. The autoclave had 18.31% significantly infected containers and produced a 70.88% moth yield. These results suggest that autoclaving is effective against Bt spores while Quorum accentuates Bt prevalence. Although autoclaving is an effective method of combating Bt, it is not suitable for use with all materials. This necessitates further research to find additional, general-use sterilization methods for mass rearing facilities, such as application of germicidal ultraviolet radiation. Identifying proper sterilization methods is essential in controlling Bt prevalence within the colony of a mass rearing system.