Acceptance by Honey Bee Guards of Non-Nestmates is not Increased by Treatment with Nestmate Odours

Honey bee, Apis mellifera, entrance guards use chemical cues to discriminate nestmates from non-nestmates. Previous research has shown that when wax combs are reciprocally swapped between two colonies, guards become more accepting of workers from the swap partner. However, when combs were transferred only one way, guards in the comb-receiver colony became more accepting of bees from the comb-donor colony, but not vice versa. Hence, the increased acceptance of non-nestmates caused by reciprocal comb swapping was not because of introduced bees acquiring odours from the transferred combs, which was surprising because comb wax was known to affect the odour of bees. In the current experiment, we caused workers to acquire either nestmate or non-nestmate odours by holding them for 15 min in a tube, which had previously held nestmates or non-nestmates and then measured their acceptance by entrance guards of nestmate or non-nestmate hives. When transferred workers had acquired odours of non-nestmates, acceptance by their own colony's guards significantly decreased to 66% from 91%. Conversely, the acceptance of non-nestmates that had acquired odours of the guards' own nestmates was unchanged, 25% vs. 25%. These results show that when equivalent changes in the odour of introduced bees are made, guards are more sensitive to changes that cause nestmates to acquire non-nestmate odours than vice versa. These results are also a likely explanation for the earlier and surprising results from the unidirectional comb swap experiment (Couvillon et al. 2007). We make a hypothesis for the underlying mechanism in terms of a multidimensional recognition cue space.