The threat of theft: the effects of a robber bee pheromone on the Tetragonisca angustula defence response

Abstract Eusocial stingless bee species are of economic and cultural importance throughout the tropics. Tetragonisca angustula is a widespread stingless bee with an unusual colony organisation, it has a separate worker sub-caste dedicated to colony defence. This defence system is likely a result of the ecological pressure brought on by the kleptoparasitic stingless bee genus Lestrimelitta . To further understand this kleptoparasitic relationship, we exposed T. angustula colonies to Citral, a robber bee pheromone, and analysed the effects of this chemical on foraging, guard number and size. A strong response to Citral by T. angustula colonies has repeatedly been reported, but whether and how Citral affects foraging and has long-term effects on defence remains unclear. We found a significant long- and short-term increase in guard number in treatment colonies, as well as a significant decrease in short-term pollen foraging (-30.8%) after treatment. Long-term exposure to Citral did not lead to a change in guard size, but we found an increase in forager size and discuss how this may strengthen colony defence during robber bee raids. While an increase in colony defence aligns with earlier reports, the observation that colonies exposed to Citral experience a reduction in pollen foraging suggest that heightened colony defence might come at a cost of reduced pollen collection even in the absence of an actual confrontation.