Agonistic interactions between Vespula vulgaris (Linnaeus) and Vespula germanica (Fabricius) (Hymenoptera: Vespidae) during foraging.

Foraging behavior is a key factor associated with the success of social insect invasions. Vespula wasps show complex behavioral patterns and social mechanisms associated with foraging, which are directly related to their invasive success in several countries worldwide. Vespula vulgaris (Linnaeus) and Vespula germanica (Fabricius) are invasive wasps, coexisting in Patagonia, showing temporal and dietary overlap. As generalist, opportunistic predators and scavengers with broad diets, these sympatric wasps share similar niches and foraging habits. We analyzed their foraging strategies and interaction, observing the behavior of each species in the presence of workers of the same species, and the other species at a given resource, directly and indirectly. Directly, from a continuous visual record, we observed and recorded the frequency of wasp's behavior at a feeder for 30 min. Indirectly, we conducted pairwise choice tests to compare wasp preference for treated and untreated feeders with visual and olfactory cues simulating the presence of wasps of the same or different species. We found consistent differences between species in aggressiveness. V. vulgaris showed a greater degree of intraspecific agonistic behavior than toward V. germanica, while V. germanica was less aggressive, and intraspecific and interspecific interactions were similar. Also, V. vulgaris preferred landing on baits without visual and olfactory cues simulating wasps presence, while V. germanica preferred baits with cues simulating its own species over baits with cues representing V. vulgaris. Our results suggest that V. germanica prioritize social facilitation as foraging strategy, while for V. vulgaris aggression is the predominant strategy.