On the relationship between aggression and reproduction in pairs of orphaned worker bumblebees (Bombus impatiens)

Abstract

This study characterized aggression and reproduction within pairs of orphaned bumblebee sisters (Bombus impatiens (Cresson, 1863)). Twenty-one pairs were filmed in the laboratory over 5–10 days. Frequencies of aggression and egg-laying were obtained for each bee, and the presence or absence of brood was manipulated. Aggression and egg-laying were more likely to co-occur in pairs placed without brood compared to pairs placed with brood. A significant positive correlation was found between members of a pair in the rates of aggression. In addition, a strong positive correlation was found in their rates of egg-laying: bees that had more sons also tended to have more nephews. The results show that under conditions of unrestricted food availability, behavioural interactions are compatible with continued reproduction by both orphaned workers. Though aggression may limit reproduction, it seems either to be an ineffective means of obtaining a reproductive monopoly in some situations and/or to be a set of behaviours invested with other possible functions.