Ascophaera: not just in larvae anymore!

Ascophaera: not just in larvae anymore!

Sarah A. Maxfield-Taylor, Sujaya Rao, and Kimberly Skyrm

Oregon State University, Dept. of Crop and Soil Science, 3017 ALS, Corvallis, OR

Worldwide, native bee declines have been attributed, in part, to disease. While diverse organisms cause diseases in bees, many of the causal agents are fungal in origin. Pathogenic fungi in the genus Ascosphaera (Ascomycota: Plectomycetes: Ascosphaearales), cause chalkbrood disease in solitary bees and honey bees. Only larval stages of these bees are affected, and the fungus has never been reported from adult bees. Here, we report the first-ever detection of Ascosphaera in adults of bumble bees, Bombus spp. The discovery was made during a larger study, the objective of which was to compare pathogens in wild and laboratory reared bumble bees in Oregon.  In 2011, wild-caught bumble bee queens belonging to five species were placed in containers in the laboratory for initiation of colonies. Queens and workers that died in rearing were frozen and subsequently dissected for detection of potential mortality factors. Unknown organisms were plated on artificial media containing broad spectrum antibiotics for isolation of the fungus and for identification using molecular markers. The results indicated that Ascosphaera was present in both workers and queens of three species, B. griseocollis, B. nevadensis, and B. vosnesenskii. Of 113 bees dissected, 13(1%) were infected. The fungus was also isolated from two larvae and from pollen pots collected from colonies of B. griseocollis. These, and other results related to associations of Ascosphaera with bumble bees in Oregon, will be presented, and the significance and implications of the discovery will be discussed.