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

To improve health and vitality of honey bees, Apis mellifera, beekeepers
can propagate stocks that demonstrate resistance to both parasites and
pathogens. Most breeding programs focus on resistance to Varroa destructor
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 Varroa resistance to colonies from a commercial source
that were not selected specifically for Varroa resistance but were
selected for “general” hygienic behavior using the freeze-killed brood
(FKB) assay. We challenged colonies within each line with Ascosphara apis,
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 Varroa and
diseases.