Inefficient task partitioning among nonhygienic honeybees, Apis mellifera L., and implications for disease transmission

Abstract

Hygienic behaviour in honeybee colonies involves the recognition and removal of diseased brood by worker bees. This task is further partitioned into subtasks of uncapping cells with diseased brood and removing the cell contents. Worker bees that express hygienic behaviour remove diseased brood from the colony before the pathogen reaches the infectious stage. Although all honeybees are capable of uncapping and removing diseased brood, only those colonies with hygienic bees, the genetic specialists, do so rapidly and hence efficiently limit disease transmission. Colonies with nonhygienic bees, however, uncap and remove diseased brood only after it becomes infectious, resulting in the handling and transmission of pathogens. To understand the behavioural repertoire of individual nonhygienic bees and how the performance of the behaviour is influenced by the presence of hygienic bees as nestmates, we observed nonhygienic bees that were maintained in colonies with varying proportions of hygienic and nonhygienic bees. Our results indicated that nonhygienic bees in mixed colonies were not stimulated to perform hygienic behaviour to a higher extent in the presence of hygienic bees. The rate, duration and probability of uncapping and removing dead brood by nonhygienic bees was significantly reduced in the presence of hygienic bees. In mixed colonies, as compared to a colony of hygienic bees, a higher proportion of uncapped cells were subsequently recapped, resulting in delayed removal of dead brood. This inefficient task partitioning would allow the pathogen to reach the infectious stage and increase the probability of disease transmission.