Bees bred for Varroa sensitive hygiene trait demonstrate resistance to chalkbrood disease

<p>To improve health and vitality of honey bees, <em>Apis mellifera</em>, beekeepers can propagate stocks that demonstrate resistance to both parasites and pathogens. Most breeding programs focus on resistance to <em>Varroa</em> <em>destructor</em> mites and/or brood pathogens. Colonies bred specifically the trait Varroa Sensitive Hygiene (VSH) have never been explicitly tested for resistance to brood disease. The goal of this study was to test if colonies bred for VSH are both mite and disease resistance. Over two years (2023 and 2024) and in two locations (University of Minnesota and the USDA-ARS lab in Baton Rouge, Louisiana), we compared colonies from the POL line bred specifically for <em>Varroa</em><em> </em>resistance to colonies from a commercial source that were not selected specifically for <em>Varroa</em><em> </em>resistance but were selected for “general” hygienic behavior using the freeze-killed brood (FKB) assay. We challenged colonies within each line with <em>Ascosphara apis,</em> that causes chalkbrood, and quantified mites, disease and hygienic behavior. Our study demonstrated that colonies from the POL line bred for VSH are just as resistant to chalkbrood as bees from a Commercial line bred for hygienic behavior by the FKB assay. Results confirmed that the POL line is more mite resistant than the Commercial, as it had significantly lower mites in two of three trials. Both the POL and Commercial colonies had high levels of hygienic behavior as measured by the FKB assay. These results indicate that honey bees selected for VSH respond to both mite-infested and disease-infected brood. Further comparative studies are needed to clarify any differences in genetic mechanisms and olfactory sensitivity mediating the VSH-trait and general hygienic behavior. On a practical level, using lines of honey bees selected for VSH in beekeeping operations could help curb losses, improve honey bee health, and reduce financial burdens caused by <em>Varroa</em> and diseases<em>. </em></p>