Physiological susceptibility and hygienic behaviour affect chalkbrood disease incidence in worker and drone larvae in honey bees (Apis mellifera L.)
Chalkbrood disease is a mycosis of honey bee (Apis mellifera) larvae caused by the heterothallic fungus Ascophaera apis. In infected colonies it is often found that drone larvae are more affected than worker larvae and this difference is attributed to the higher probability of chilling of drone brood. Given the great differences found between worker and drone larvae, however, it would be expected to find differential physiological resistance to chalkbrood disease. Additionally, if hygienic behaviour of adult bees (uncapping of cells containing dead brood and its subsequent removal) is expressed differently in worker and drone cells, it may differentially affect the proportion of mummified larvae of each sex. The goal of this research was to determine how physiological resistance and hygienic behaviour affect chalkbrood incidence in worker and drone larvae. Firstly, the proportion of worker and drone larvae mummified after receiving food containing A. apis spores was determined. Then hygienic behaviour in relation to dead brood of both sexes was evaluated. It was found that drone larvae mummify and have fruiting bodies in a greater proportion than worker larvae and that hygienic behaviour is more efficient in relation to worker rather than drone cells. These results indicate that physiological susceptibility and hygienic behaviour are two factors that could explain satisfactorily the greater proportion of mummified drones found in diseased colonies.