Variable susceptibility to chalkbrood infection between Russian honey bee lines and life stages

Ascosphaera apis is the causal agent of the mycosis known as chalkbrood disease. Once ingested, the fungal spores piece through larval honey bee guts, producing a whitish “mummy,” reducing brood populations, and draining colony resources. Although preventative measures can be implemented to lessen the spread and severity of chalkbrood, no effective treatment currently exists to cure an infected colony. This, combined with the regionally-variable severity of chalkbrood disease has driven interest in the development of additional cultural controls, namely, genetically resistant honey bee lines. Russian honey bees have demonstrated increased disease and pest resistance compared to commercially available Italian stocks and previous investigations have also shown some degree of inconsistent A. apis resistance. Here, we exposed colonies divided between 11 Russian honey bee breeding lines to A. apis spores and compared relative susceptibility among lines by counting mummies produced and periodically assessing colony health. After identifying the most and least susceptible lines, we then in vitro reared larvae from the corresponding colonies to determine if colony phenotypes were attributable to larval resistances. In vitro reared larvae were orally inoculated with A. apis and subsequent mortality was compared. We expect to see a range of resistances across the 11 tested breeding lines, potentially correlating to the hygienic behavior of each colony. Our results will help expand our understanding of genetic disease resistances in honey bees and our disease prevention toolkits, both of which will ultimately contribute toward the sustainability of the apicultural and agricultural industries.