Development of Bacillus thuringiensis as a Varroa mite biocontrol
By Kirk E. Anderson and Vincent Ricigliano
Conducted at Carl Hayden Bee Research Center Tucson AZ.
We have made significant progress in the development of a Varroa mite biocontrol strategy.Over the last 10 months we have successfully developed methodologies for isolation, genetic characterization, and toxicity assays (in vitro and host-associated) of candidate Bacillus thuringiensis (BT) strains.
Initial and widespread sampling of Varroa mite populations included two sources of commercial migratory colonies. Multi-gene analysis of the cultured BT enabled the identification of novel isolates and ensured genetic diversity and variable toxicity of our BT strain bank. Using in vitro bioassays we continue to identify an increasing number of BT strains exhibiting acaricidal potential (Fig. 1). Strains with strong in vitro effects will be field tested for toxicity to both bees and mites at the colony level over the coming months and fall of 2017. We are presently assessing efficacy in cage experiments that include host-associated components. These findings confirm and extend the results shown in table 1, and will be discussed at the meeting in November. Conclusive colony-level testing will require another yearly cycle of Varroa, allowing time to adequately design and quantify the critical fall treatment.
Figure 1. Bar graph depicting survival (±SE) of Varroa destructor 48 hours after treatment. Results are based on in-vitro assays in culture plates containing six different bacterial strains selected for their putative insecticidal potential. We introduced non-toxic E. coli as a control.