First Detection of the Larval Chalkbrood Disease Pathogen Ascosphaera apis (Ascomycota: Eurotiomycetes: Ascosphaerales) in Adult Bumble Bees

Abstract

Fungi in the genus Ascosphaera (Ascomycota: Eurotiomycetes: Ascosphaerales) cause chalkbrood disease in larvae of bees. Here, we report the first-ever detection of the fungus in adult bumble bees that were raised in captivity for studies on colony development. Wild queens of Bombus griseocollis, B. nevadensis and B. vosnesenskii were collected and maintained for establishment of nests. Queens that died during rearing or that did not lay eggs within one month of capture were dissected, and tissues were examined microscopically for the presence of pathogens. Filamentous fungi that were detected were plated on artificial media containing broad spectrum antibiotics for isolation and identification. Based on morphological characters, the fungus was identified as Ascosphaera apis (Maasen ex Claussen) Olive and Spiltoir, a species that has been reported earlier only from larvae of the European honey bee, Apis mellifera, the Asian honey bee, Apis cerana, and the carpenter bee Xylocopa californica arizonensis. The identity of the fungus was confirmed using molecular markers and phylogenetic analysis. Ascosphaera apis was detected in queens of all three bumble bee species examined. Of 150 queens dissected, 12 (8%) contained vegetative and reproductive stages of the fungus. Both fungal stages were also detected in two workers collected from colonies with Ascosphaera-infected B. nevadensis queens. In this study, wild bees could have been infected prior to capture for rearing, or, the A. apis infection could have originated via contaminated European honey bee pollen fed to the bumble bees in captivity. Thus, the discovery of A. apis in adult bumble bees in the current study has important implications for commercial production of bumble bee colonies and highlights potential risks to native bees via pathogen spillover from infected bees and infected pollen.

Viral transmission in honey bees and native bees, supported by a global black queen cell virus phylogeny

“…Additionally, we found that BQCV isolated from the fungus Ascosphaera apis from honey bees in Maryland clustered with our New York honey bee and native bee samples, illustrating the close relatedness of the virus and potential for virus crossover between fungal and bee species. Some bee viruses can infect and replicate within Ascosphaera apis, which causes chalkbrood in honey bees (Li et al, 2014) and is known to be pathogenic in bumble bees (Maxfield-Taylor et al, 2015). Both pathogenic and saprotrophic strains have been found in solitary bees (Osmia cornifrons) (Hedtke et al, 2015).…”

Characterization of the Beekeeping Value Chain: Challenges, Perceptions, Limitations, and Opportunities for Beekeepers in Kayonza District, Rwanda

“…The more elderly beekeepers showed more experience and understanding in the interpretation of the findings of these inspections. However, there was a common misconception that moulds indicated cold instead of chalkbrood as the primary problem [49][50][51]. This showed that inspection alone was not sufficient in disease diagnosis.…”

Microbial Diversity Associated with the Pollen Stores of Captive-Bred Bumble Bee Colonies

“…There are several documented cases of pathogen transmission from honey bees to bumble bees in Europe and North America [106][107][108][109][110][111]. The honey bee pathogen A. apis has been detected within the colonies of many captive-reared bumble bees species, including B. griseocollis, B. nevadensis, B. vosnesenskii, and B. terrestris [112]. A recent study reveals that infected colonies of B. terrestris showed symptoms similar to that of chalkbrood disease in honey bees [100].…”

“…Another potential route of exposure is the use of infected honey bee-collected pollen as diet for the developing colonies reared in captivity [118]. Contaminated honey bee pollen, which often carries bumble bee pathogens, has been reported to cause widespread infections at commercial rearing facilities and can lead to rapid declines in bumble bee populations [112,[118][119][120][121]. The risk of pathogen spillover from the release of such infected colonies to native bee populations poses a significant threat to the health of wild bees [35,38,41,118,120,122,123].…”