Allee effects in an invasive social wasp: an experimental study in colonies of Vespula germanica

Abstract

Allee effects rely on the existence of mutually beneficial intraspecific interactions that increaseindividual fitness and per capita growth rate, as the number of individuals in a population or groupincreases. When the number of individuals falls below a given number, the success of a group orpopulation drops. Social insects heavily rely on cooperation between individuals for various taskssuch as foraging and breeding. In this study, we experimentally explored component Allee effectsand the underlying mechanisms in colonies of the social wasp Vespula germanica. After the removal of workers, we counted the number of gynes produced, estimated the body mass index as a proxy of their quality, and registered the protein-food collected by foragers in colonies. Our research revealed a correlation between the decrease in worker population and a subsequent decrease in the production of gynes. However, the removal of workers did not impact the quality of the produced gynes or the quantity of protein-food collected by the colonies. These findings highlight the crucial role of the worker caste in the success of eusocial species and suggested an ability of workers to perform multiple tasks that enable colonies to respond to disturbances. Additionally, our study provides the first evidence of Allee effects at the colony level of V. germanica, with potential practical implications for managing this invasive species.