Vespula wasps show consistent differences in colony-level aggression over time and across contexts

Abstract

Social wasps are well-known for aggressively defending their nests when these are approached, threatened, or directly attacked. However, the variability, consistency, and the determinants of such defensive and aggressive responses of wasp colonies are largely unknown. Here, we quantify the aggressiveness of Vespula vulgaris and V. germanica wasp colonies to determine if colonies exhibit consistent differences in aggression across different spans of time and disturbance contexts, and if colony-level aggression is linked to intrinsic and/or extrinsic parameters that seem to predict the aggressive response of other social insects. We conducted three experiments in locations throughout the South Island of New Zealand, where we quantified foraging activity, as well as unprovoked, and provoked (post-disturbance) colony aggression across short (one day), moderate (one week), and long (one month) spans of time. We also estimated the colony investment into nest size and pupae, as well as the temperature near the nest entrance, to determine if these intrinsic and extrinsic parameters could predict colony-level defensive response to a simulated predator attack. We found that, across all three durations of time, some wasp colonies are consistently aggressive, while other colonies exhibit little to no aggressive response to disturbance. We show that colony aggression levels are consistent across contexts over moderate and long spans of time, and that the intensity of colony response is consistent under different types of nest disturbance. The aggressive response of wasp colonies could not be predicted by activity level, temperature, or investment into nest or pupae. The existence of consistent differences in wasp colony aggression suggests that both aggressive and non-aggressive behavioral types can have fitness benefits in a population. Aggressive colonies might defend their nests more effectively, deterring potential predators better than docile colonies. On the other end, less aggressive colonies could go unnoticed by humans and develop undisturbed. Our study further suggests that different mechanisms could underlie the evolution of a wide spectrum of aggressive colony phenotypes in the eusocial Hymenoptera.