Odour transfer between colonies of the stingless bee Frieseomelitta varia demonstrates that entrance guards use an "undesirable-absent" cue recognition system.

In group-level recognition, discriminators use sensory information to distinguish group members and non-members. For example, entrance guards in eusocial insect colonies discriminate nestmates from intruders by comparing their odour with a template of the colony odour. Despite being a species-rich group of eusocial bees closely related to the honey bees, stingless bee nestmate recognition is a relatively little-studied area. We studied Frieseomelitta varia, a common Brazilian species of stingless bee known as marmelada. By measuring the rejection rates of nestmate and non-nestmate worker bees by guards, we were able to show that guards became significantly less accepting (from 91 to 46%) of nestmates that had acquired odour cues from non-nestmate workers; however, guards did not become significantly more accepting (from 31 to 42%) of non-nestmates that had acquired equivalent amounts of odour cues from the guard's nestmates. These data strongly suggest that guards use an "undesirableabsent" system in recognition, whereby incoming conspecific workers are only accepted if undesirable cues are absent, despite the presence of desirable cues. We suggest that an undesirableabsent system is adaptive because robbing by conspecifics may be an important selective factor in F. varia, which would lead to selection for a non-permissive acceptance strategy by guards.