The stinging response of the common wasp ( Vespula vulgaris ): plasticity and variation in individual aggressiveness

We studied the variability and plasticity of individual aggressiveness in a social insect, describing and quantifying the sting extension response (SER) of the common wasp Vespula vulgaris . As a proxy for individual aggressiveness we measured the SER of individual wasps, scoring the extent by which the sting was extruded in response to a mild electric shock (7.5 or 12 V for 2 s) on a scale from 0 to 1. We found that wasps vary greatly in their stinging propensity and aggression thresholds and that individuals change their SER during their life. Extremely aggressive or docile phenotypes, showing at first consistent mutual differences on different days, tended to converge over time and developed comparable SER responses later in their life. Older individuals tended to be more aggressive. Wasp size was not related to the stinging phenotype. Wasp foragers had a less pronounced sting extension than individuals previously involved in nest defense. For the same individual, the aggressive response was proportional to the intensity of the negative stimulus. We discuss the advantages of the SER bioassay as a tool to measure individual aggressiveness, plasticity and inter-individual variability in the Aculeata group, and its great potential in comparative and learning studies.