Pest description BOB larvae become infected by ingesting spores from contaminated pollen and nectar provisions. Long filaments penetrate the gut epithelium and cause death of the immature bee. Spores are spread to adult BOBs when they chew their way through a nest cell containing a dead larva. These spores can also be deposited on pollen and nectar provisions as the nest is built. Some infested BOBs that die during pupation after consuming the entire spore-containing provision show a continuous darkened layer of chalkbrood spores throughout the body. When infested BOBs do not fully consume contaminated provisions, the larvae are only partially filled with spore aggregations. Uninfected newly emerging adult BOBs may become infected with spore dust when they chew their way through a nest cell containing a chalkbrood-infested larva cadaver. Then these spores may be transferred into the provisions of the new nest.
Management BOB immatures should be reared at appropriate temperatures. Over-winter BOBs for at least 180 days ≤ 45°F and emerge 1 to 7 days after warming between 72°-78°F. Removal of infested cells is a simple way to control chalkbrood. The use of new nesting cavities is important, as spores can remain viable for years. If reusing nesting materials, rinsing this equipment with a light bleach solution of one part bleach and one part water after cocoons are removed can kill leftover fungal spores responsible for chalkbrood. In winter, randomly inspect 10% of nests for chalkbrood cadavers (and presence of other beetle and mite parasites by visually observing cocoons). If more than 10% of nests examined are diseased or parasitized, inspection of all remaining nests is necessary.