Escalation of Aggressive Interactions During Staged Encounters in Halictus ligatus Say (Hymenoptera: Halictidae), with a Comparison of Circle Tube Behaviors with Other Halictine Species'

Circle tube experiments on the primitively eusocial bee, Halictus ligatus, were performed for a variety of combinations of caste and size. Push, Lunge, and Back without reverse behaviors enabled us to determine the dominant individual in most comparisons. Behavioral differences were readily detected within the first 15 min except for different-size forager–forager and same-size foundress–foundress pairs, for which 30 min of observations was required. In same-size forager–forager pairs, no differences in behaviors between individuals were detected even after 90 min. In extended observations, decreases in the frequency of the mild dominant behaviors were accompanied by a switch to the highly aggressive mandibular hold on the neck, particularly in different-size foundress–foundress and gyne–gyne pairs. Three workers were killed by their own queen as a result of this escalation of aggression. We discuss caste-based differences in the circle tube setting in terms of behaviors expected under more normal conditions and compare our data with published results from other species.