Genetic variation of Ascosphaera apis and colony attributes do not explain chalkbrood disease outbreaks in Australian honey bees.

Chalkbrood infection caused by the fungus Ascosphaera apis currently has a significant impact on Australia's apicultural industry. We investigated the genetic variation of A. apis and colony and apiary level conditions to determine if an emerging, more virulent strain or specific conditions were responsible for the prevalence of the disease. We identified six genetically distinct strains of A. apis, four have been reported elsewhere and two are unique to Australia. Colonies and individual larvae were found to be infected with multiple strains of A. apis, neither individual strains, combinations of strains, or obvious colony or apiary characteristics were found to be predictive of hive infection levels. These results suggest that host genotype plays an important role in colony level resistance to chalkbrood infection in Australia.

Hygienic behaviour selection via freeze-killed honey bee brood not associated with chalkbrood resistance in eastern Australia.

Hygienic behaviour is a social immune response in honey bees shown to help provide resistance to honey bee pests and diseases. A survey of hygienic behaviour and brood diseases was conducted on 649 colonies in eastern Australia to initiate a selective breeding program targeting disease resistance and provide a level of resistance to Varroa (Varroa destructor Anderson and Trueman and V. jacobsoni Oudemans) mites should they become established in Australia. The test population showed a remarkably high baseline level of hygienic behaviour with 17% of colonies meeting or exceeding breeding selection thresholds. Colonies belonging to a breeding program were 5.8 times more likely to be highly hygienic and colonies headed by queens raised from hygienic queen mothers were 2.2 times more likely. Nectar availability (nectar yielding flowering plants within honey bee forage range) influenced hygienic behaviour expression but was not a significant predictor of level of hygienic behaviour. Surprisingly, hygienic behaviour was not a significant predictor of the presence of infection of the honey bee brood disease chalkbrood (Ascosphaera apis) and was not influential in predicting severity of chalkbrood infection in surveyed honey bee colonies. This study, along with reports from commercial beekeepers that chalkbrood infection is on the rise, warrants a deeper exploration of the host-pathogen relationship between Apis mellifera and Ascosphaera apis in Australia.