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Many diseases and pathogens infect honey bee colonies, but chalkbrood is likely the most common among beekeepers. Ascosphaera apis causes chalkbrood, which is a fungal brood disease. Beekeepers commonly detect chalkbrood in the spring because chalkbrood is considered a stress-related disease. However, chalkbrood is observed throughout the year. Many times, chalkbrood becomes established in colonies because of many interacting factors, such as environmental stressors, genetic makeup of colonies and beekeeping practices. Chalkbrood contaminates larvae when nurse bees admix chalkbrood spores with brood food. The fungal spores out-compete larvae for food and eventually, turn larvae into “chalk-like” mummies. Beekeepers can observe chalkbrood in many colors, ranging from white to grey to black. As larvae turn black, the chalkbrood begins producing fruiting bodies, which are highly infectious. Beekeepers can find these mummies at the entrance or bottom boards, especially if chalkbrood is widespread. At this point these mummies can spread spores to other colonies in the area. Chalkbrood often infects 3-4 day larvae, and can be found as uncapped or capped larvae. If the colony shakes a frame with capped chalkbrood, the frame will rattle when shaken.  

Read the fully article here: Chalkbrood: A common spring disease — The Daily Guide to Beekeeping