Chalkbrood, a fungal brood disease of honey bees, is reportedly on the increase in Pennsylvania. The disease is caused by the spore-forming fungus, Ascosphaera apis. Worker, drone, and queen larvae are all susceptible. Dead larvae are chalky white and usually covered with filaments (mycelia) that have a fluffy, cottonlike appearance. These mummified larvae may be mottled with brown or black spots, especially on the ventral sides, due to the presence of spore cysts or fruiting bodies of the fungus.

Diseased larvae can be found throughout the brood-rearing season, but are most prevalent in late spring when the brood nest is rapidly expanding. Chalkbrood usually disappears or declines as the air temperature rises in the summer. Affected larvae are found on the outer fringes of the brood nest where there are not enough nurse bees to maintain brood nest temperature. Brood cells can be either sealed or unsealed. Young pupae or recently sealed larvae are most susceptible. Infected larvae, stretched out in their cells in an upright position, are removed by nurse bees two to three days after symptoms first appear. Dead larvae (mummies) are often found in front of the hive, on the landing board, or in the pollen trap. In strong colonies, most of these mummies will be discarded by worker bees outside of the hive, thus reducing the possibility of reinfection from those that have died from the disease.

Spores of the fungus are ingested with the larval food. The spores germinate in the hind gut of the bee larva, but mycelial (vegetative) growth is arrested until the larva is sealed in its cell. At this stage, the larva is about six or seven days old.

The mycelial elements break through the gut wall and invade the larval tissues until the entire larva is overcome; this process generally takes from two to three days.

Spores remain virulent for years. Therefore, infected pieces of equipment, especially brood combs, are a reservoir for further infection. Chalkbrood usually does not destroy a colony. When the disease is serious, however, it can prevent normal population buildup and surplus honey production. Research has shown that the spores are easily passed from bee to bee. Therefore, drifting and robbing bees are potentiai vectors of the disease. Both workers and queens taken from infected colonies can transmit infection to healthy colonies. Colonies fed pollen collected from infected colonies will also contract the disease.

Chalkbrood infections are not always visible in the broodnest. Therefore, beekeepers who collect pollen to sell or to feed to their bees should check the pollen and pollen traps from each colony for whole mummies or mummy parts. No treatment is presently available for control.