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United States Department of Agriculture

Agricultural Research Service

Title: Chalkbrood

Author
item James, Rosalind

Submitted to: Bee Culture
Publication Type: Book / Chapter
Publication Acceptance Date: October 16, 2002
Publication Date: May 1, 2007
Citation: James, R.R. 2007. Chalkbrood. In: Shimanuki, H., Flottum, K., Harman, A., editors. ABC & XYZ of Bee Culture. 41st edition. Medina, OH: A.I. Root Company. p. 201.

Interpretive Summary: This disease, named for the chalky appearance of the dead infected bee larvae, is caused by fungi (molds) in the genus Ascosphaera. Chalkbrood fungi have only been found in association with bees, and most species infect the larvae of solitary bees, such as the alfalfa leaf cutting bee. At least 21 species of chalkbrood fungi have been found in N. America, but Ascosphaera apis is the only one known to infect honey bees. Ascosphaera aggregata is the species most common in the alfalfa leaf cutting bee. Infections become apparent in the late larval and early pupal stages but may show up in younger larvae if a colony or nest is heavily infected. In honey bees, both worker and drone brood can become infected. Chalkbrood has been reported from throughout North America, Europe, Asia, and Australia. Ascosphaera apis, the honeybee chalkbrood, was probably introduced into the U.S. from Europe. The source of chalkbrood in leafcutting bees is uncertain. Ascosphaera aggregata, the alfalfa leafcutting bee chalkbrood, likely came from Europe as well, but other chalkbroods that infect this bee may be native to the U.S. Bee larvae become infected with the disease when they consume fungal spores in their food. Honey bee larvae tend to be more prone to infection when the brood are chilled. The typical high temperatures in the brood chamber may inhibit the pathogen, and this may also be why honey bees appear to be less susceptible to chalkbrood infections than the alfalfa leafcutting bee. Leafcutting bees are solitary and brood temperatures are not controlled as in a honey bee colony. No effective chemical control has been found for chalkbrood in either honey bees or leafcutting bees. In honey bees, managing for strong colonies has proved beneficial in preventing the disease. Management strategies include requeening with a young queen, moving colonies into full sunlight (especially in cool climates), adding supers only as needed to keep the size of the hive to a volume that the bees can keep dry and warm, exchanging wet bottom boards with dry ones, placing hives where they will remain warm and dry, and strengthening weak colonies by merging them with other colonies. Control of chalkbrood in the alfalfa leafcutting bee is done mostly through sanitation methods. Bee cells are removed from nesting boards at the end of the season, then tumbled to break the cells apart from each other. Once the cells are removed from the boards, the boards can be disinfected before they are nested in again the next year. Boards can be disinfected by either dipping them in chlorine or baking them at high temperatures. Removing the cells from the boards and breaking apart the nests also reduces the chance that emerging bees will become contaminated with spores. If the nests are not removed from the boards, emerging females must chew their way through siblings who have died from chalkbrood and are blocking the way out of the nest. These dead bees act as a source of contamination.

Technical Abstract: This disease, named for the chalky appearance of the dead infected bee larvae, is caused by fungi (molds) in the genus Ascosphaera. Chalkbrood fungi have only been found in association with bees, and most species infect the larvae of solitary bees, such as the alfalfa leaf cutting bee. At least 21 species of chalkbrood fungi have been found in N. America, but Ascosphaera apis is the only one known to infect honey bees. Ascosphaera aggregata is the species most common in the alfalfa leaf cutting bee. Infections become apparent in the late larval and early pupal stages but may show up in younger larvae if a colony or nest is heavily infected. In honey bees, both worker and drone brood can become infected. Chalkbrood has been reported from throughout North America, Europe, Asia, and Australia. Ascosphaera apis, the honeybee chalkbrood, was probably introduced into the U.S. from Europe. The source of chalkbrood in leafcutting bees is uncertain. Ascosphaera aggregata, the alfalfa leafcutting bee chalkbrood, likely came from Europe as well, but other chalkbroods that infect this bee may be native to the U.S. Bee larvae become infected with the disease when they consume fungal spores in their food. Honey bee larvae tend to be more prone to infection when the brood are chilled. The typical high temperatures in the brood chamber may inhibit the pathogen, and this may also be why honey bees appear to be less susceptible to chalkbrood infections than the alfalfa leafcutting bee. Leafcutting bees are solitary and brood temperatures are not controlled as in a honey bee colony. No effective chemical control has been found for chalkbrood in either honey bees or leafcutting bees. In honey bees, managing for strong colonies has proved beneficial in preventing the disease. Management strategies include requeening with a young queen, moving colonies into full sunlight (especially in cool climates), adding supers only as needed to keep the size of the hive to a volume that the bees can keep dry and warm, exchanging wet bottom boards with dry ones, placing hives where they will remain warm and dry, and strengthening weak colonies by merging them with other colonies. Control of chalkbrood in the alfalfa leafcutting bee is done mostly through sanitation methods. Bee cells are removed from nesting boards at the end of the season, then tumbled to break the cells apart from each other. Once the cells are removed from the boards, the boards can be disinfected before they are nested in again the next year. Boards can be disinfected by either dipping them in chlorine or baking them at high temperatures. Removing the cells from the boards and breaking apart the nests also reduces the chance that emerging bees will become contaminated with spores. If the nests are not removed from the boards, emerging females must chew their way through siblings who have died from chalkbrood and are blocking the way out of the nest. These dead bees act as a source of contamination.

Last Modified: 10/30/2014
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