* Caused by: Ascophaera apis * Spore-forming fungus * Brood disease Chalkbrood, a fungal brood disease of honey bees, is caused by the spore-forming fungus, Ascophaera apis. Worker, drone, and queen larvae are all susceptible. 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. When larvae are about six or seven days old and sealed in their cells, the mycelia 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.