En garde: rapid shifts in honeybee, Apis mellifera, guarding behaviour are triggered by onslaught of conspecific intruders

In a recognition context, discriminating agents decide whether to accept or to reject. In the honeybee, entrance guards distinguish between nestmates and intruders. Those below a threshold of dissimilarity are accepted. However, the threshold is dependent on ecological conditions and may shift to become either restrictive or permissive, depending on the frequency of intrusion and cost of admitting an intruder. Previous research on the honeybee has shown that both the number of guards and their acceptance threshold to conspecific non-nestmates can change dramatically over weeks owing to changing nectar availability and robbing intensity. This project investigated whether these changes could also occur rapidly, over minutes, in response to sudden increases in conspecific intruders (robber bees). We induced high levels of intrusion at nest entrances and determined changes in the number of guards, the number of fights per guard, and the acceptance thresholds of guards. Our results show a rapid response within 15 min. At the level of individual guards, acceptance declined from 83 to 55% for nestmates and 67 to 43% for conspecific non-nestmates. Also, per individual guard, mean fights increased from 0.005 to 0.06 fights/guard. At the colony level, the mean number of guards at the entrance rose from 1.9 to 2.3, and overall acceptance in a 3-min trial declined from 74 to 52% for nestmates and 59 to 30% for conspecific non-nestmates. These results show that honeybees can make rapid behavioural shifts at both the colony and the individual levels. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.