Adaptive shifts in honey bee (Apis mellifera L.) guarding behavior supportpredictions of the acceptance threshold model

The acceptance threshold model predicts that in a fluctuating environment a recognition system should be adaptive rather than fixed. In particular, di scriminating individuals, such as guards at a nest entrance, should be less permissive to conspecifics when both the frequency of non-nest-mate contac t and the cost of accepting non-nest mates is high. We tested these predict ions by studying honey bee guarding during a period in which nectar conditi ons changed from dearth to abundance. Initially, during nectar dearth, indi vidual guards accepted 80% of introduced nest mates and 25% of non-nest mat es. As nectar conditions improved, both the intensity of robbing and guardi ng and the cost of non-nest-mate acceptance declined. In response, individu al guards became more permissive to nest mates and non-nest mates until eve ntually an "accept-all" threshold occurred-all nest mates and non-nest mate s were accepted. These data are consistent with a shifting acceptance thres hold and provide the first field data to support the model. A simple linear relationship occurred between the number of guards and the number of fight s, 9:1, observed at the hive entrance, suggesting that guarding may be regu lated by intruder intensity or otherwise regulated in an adaptive manner.