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

Abstract

Allee effects are based on the existence of mutually beneficial intraspecific interactions that individual fitness and per capita growth rate increase as the number of individuals in a population or group increase. Allee effects are often noted when individuals fall below a given number and the success of a group or population drops. In eusocial insects, cooperation is an evident defining feature since conspecifics are essential to successfully perform different tasks such as foraging and breeding. Such interactions suggest that social insects are susceptible to Allee effects. We studied Allee effects in the eusocial yellowjacket wasp Vespula germanica. We experimentally explored component Allee effects and the underlying mechanism through the removal of workers in experimental colonies. We measured the number of gynes produced, the body mass index of gynes and the amount of protein food collected by foragers in nests with different proportional change of number of workers. We found that the proportional change of number of workers was associated with a reduction in the number of gynes produced. Also, the amount of protein-food collected increased with the colony size. Our results highlight the importance of the worker caste in the success of eusocial species. We also provide evidence in Allee effects at nest level of V. germanica for the first time, which may have practical implications for the management on this invasive wasp.