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Title: Water requirements of the fungus Ascosphaera apis, and spatial analysis of growth rate as an illustration of predicting favorable conditions in a honey bee pathogen-colony model

Author
item YODER, JAY - Wittenberg University
item NELSON, BLAKE - Wittenberg University
item MAIN, LEIGHANNE - Wittenberg University
item LORENZ, ANDRE - Wittenberg University
item JAJACK, ANDREW E - University Of Cincinnati
item Aronstein, Katherine

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2016
Publication Date: 7/27/2016
Citation: Yoder, J.A., Nelson, B.W., Main, L.R., Lorenz, A.L., Jajack, A., Aronstein, K.A. 2016. Water requirements of the fungus Ascosphaera apis, and spatial analysis of growth rate as an illustration of predicting favorable conditions in a honey bee pathogen-colony model. Applied and Environmental Microbiology. pg. 1-9.

Interpretive Summary: The purpose with this study is to provide insight into the association between water activity in the bee colony and incidence of chalkbrood disease caused by the entomopathogenic fungus, Ascosphaera apis. Water activity-temperature relationships are examined, with the goal of exploring key survival elements of A. apis within the bee colony. Our experiments also seek to determine whether there is variation with regard to water requirements in different isolates of A. apis, by comparing one isolate from Arizona, two from Louisiana, and one isolate that was revived from chalkbrood-infected frozen bee larvae after many years of storage. In particular, we will investigate water requirements for A. apis spore production at documented temperatures within the hive. We are testing the hypothesis that water activity may affect the ability of A. apis to grow and produce spores, and that different isolates may have different water requirements that could account for differences in virulence as related to the production of ascospores. This new study provides the biological data for monitoring and early prediction of honey bee fungal disease outbreaks and can be used in conjunction with latest wireless sensor technology.

Technical Abstract: We report an approach to visualize traditional growth curve data by conceptualizing them into a three-dimensional projection based on the honey bee fungal pathogen, Ascosphaera apis. This approach brings together habitat conditions within the colony, pathogenesis of the disease, and factors limiting to fungus growth: water activity (aw) and temperature. Features of A. apis were a high water requirement, 0.85-0.90 aw at 25°C/30°C, 0.90-0.95 aw at 35°C, and a minimum water activity of 0.95 aw to produce spores. Growth rates varied between isolates; although one from Louisiana was similar to one from Arizona, two other Louisiana isolates displayed lower growth rates. None of these characteristics changed as the result of cycling, or descending/ascending between low and high water activity media, implying that A. apis cannot be made more dry- or wet-adapted. Temperature and relative humidity fluctuations within the colony in early spring as brood production increases facilitate pathogenesis of chalkbrood disease. A. apis has a high water requirement for spore production, and incidence of infection and transmission via spores can be critically limited by healthy bees that keep the internal brood area hot and dry. This new study provides the biological data for monitoring and early prediction of honey bee fungal disease outbreaks and can be used in conjunction with latest wireless sensor technology