CHALKBROOD DEVELOPMENT IN HONEYBEE BROOD UNDER CONTROLLED CONDITIONS

Third instar larvae from a honeybee colony were fed with high doses of spores of Ascosphaera apis, the causative agent of chalkbrood disease. Optimal survival of spores was detected during a short period after sealing the cell and before larval spinning by culture of the gut contents removed from 4 stages of brood development. The inocula (5 x 10(5) spores/larva) did not induce the disease and were not present in the digestive tract before pupation. In a second experiment, third instar larvae, fed with the same amounts of spores as before, received a cooling stress (22 +/- 2-degrees-C, for 24 h). When chilling was applied 24 h before or after operculation, mummification occurred in the majority of larvae (59.6 and 65.5%, respectively). Chilling of older brood (spinning larvae or pupa) produced a much lower incidence of chalkbrood. This confirms the need for predisposing conditions over a short period of brood development for the development of this disease.