Influence of colony genotypic composition on the performance of hygienic behaviour in the honeybee, Apis mellifera L

Hygienic behaviour, an intranidal task performed by middle-aged worker bees is an important behavioural mechanism of resistance to disease and to attack by Varroa destructor, an ectoparasitic mite. We studied the effect of a colony's genotypic composition on the expression of this behaviour among worker bees by creating normal age-structured colonies with different proportions of bees belonging to hygienic and nonhygienic lines. We established four colonies with 0, 25, 50 or 100% of worker bees belonging to the hygienic line. Analyses of the behaviour of hygienic bees in these colonies indicated that the performance of hygienic behaviour depended on the proportion of hygienic bees in the colony. Hygienic bees in the 25% hygienic colony performed the behaviour well beyond middle age and were more persistent at the task compared with bees from the same genetic line in the other colonies. However, the colony with all worker bees from the hygienic line was more efficient in achieving the task despite a lack of persistence. We also observed that in the colony with 50 and 100% hygienic bees, the behaviour was partitioned into subtasks, and some bees performed the subtask of uncapping cells at higher frequencies than the subtask of removing cell contents. These results suggest that a colony's genotypic composition influences the performance and partitioning of hygienic behaviour. We propose that the performance of hygienic behaviour and its partitioning into subtasks could be determined by response thresholds of individual worker bees and that the rate of behavioural ontogeny may be controlled by the demand for specific tasks.