Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/15/2005
Publication Date: 10/1/2005
Citation: James, R.R., Skinner, J.S. 2005. PCR diagnostic methods for Ascosphaera infections in bees. Journal of Invertebrate Pathology. 90:(2):98-103. Interpretive Summary: Chalkbrood is a serious disease affecting bees. This disease is caused by fungi called Ascosphaera, but it is difficult to tell the different Ascosphaera species apart because they all look very similar. Most identifications are based on the size and shape of the spores and spore-producing structures. Unfortunately, much overlap occurs in the size of these structures, and some Ascosphaera species will not produce spores when grown on a culture plate, they must have a host. We report a quick and reliable diagnostic method for identifying Ascosphaera infections in bees using DNA markers. We can identify any Ascosphaera fungus as such, and can differentiate species for those known to occur in leafcutting bees and honey bees. Using these methods, chalkbrood can be detected and identified from samples of bees, including bees that have not yet developed disesase symptoms. Furthermore, our diagnostic methods can detect co-infections of multiple Ascosphaera species in a single host.
Technical Abstract: Fungi in the genus Ascosphaera are the causative agents of chalkbrood, a major disease affecting bee larval viability. Identification of individual Ascosphaera species based on morphological features has been difficult due to a lack of distinguishing characteristics. Most identifications are based on the size and shape of the ascomata, spore balls and conidia. Unfortunately, much overlap occurs in the size of these structures, and some Ascosphaera species will not produce sexual structures in vitro. We report a quick and reliable diagnostic method for identifying Ascosphaera infections in Megachile bees (leafcutting bees) using PCR markers that employs genus-specific primers for Ascosphaera, and species-specific primers for species known to occur in Megachile. Using these methods, species identifications can be performed directly on bees, including asymptomatic individuals. Furthermore, the PCR markers can detect co-infections of multiple Ascosphaera species in a single host. We also identified a marker for A. apis, the predominant cause of chalkbrood in Apis mellifera, the honey bee. Our diagnostic methods eliminate the need for culturing samples, and could be used to process a large number of field collected bee larvae.