Social encapsulation of the small hive beetle (Aethina tumida Murray) by European honeybees (Apis mellifera L.)

Summary

European and African subspecies of honeybees (Apis mellifera L.) utilize social encapsulation to contain the small hive beetle (Aethina tumida Murray), a honeybee colony scavenger. Using social encapsulation, African honeybees successfully limit beetle reproduction that can devastate host colonies. In sharp contrast, European honeybees often fail to contain beetles, possibly because their social encapsulation skills may be less developed than those of African honeybees. In this study, we quantify beetle and European honeybee behaviours associated with social encapsulation, describe colony and time (morning and evening) differences in these behaviours (to identify possible circadian rhythms), and detail intra-colonial, encapsulated beetle distributions. The data help explain the susceptibility of European honeybees to depredation by small hive beetles. There were significant colony differences in a number of social encapsulation behaviours (the number of beetle prisons and beetles per prison, and the proportion of prison guard bees biting at encapsulated beetles) suggesting that successful encapsulation of beetles by European bees varies between colonies. We also found evidence for the existence of circadian rhythms in small hive beetles, as they were more active in the evening rather than morning. In response to increased beetle activity during the evening, there was an increase in the number of prison guard bees during evening. Additionally, the bees successfully kept most (~93%) beetles out of the combs at all times, suggesting that social encapsulation by European honeybees is sufficient to control small populations of beetles (as seen in this study) but may ultimately fail if beetle populations are high.