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

Background/Question/Methods

Allee effects are based on the existence of mutually beneficial intraspecific interactions which make individual fitness and per capita growth rate increase along with the increase in the number of individuals in a population or group. 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. In nests with different removal percentages, we measured the number of gynes produced, the body mass of gynes and the amount of protein-food collected by foragers.

Results/Conclusions

We found that the worker removal was associated with a reduction in the number of gynes produced and affected food gathering amounts. Also, colonies in which worker removal was higher than 44.4% did not produce any gynes. We suggest that a possible mechanism that could be producing the component Allee effect is cooperative food collecting. Our results highligh the importance of the worker caste in the success of eusocial species. We also provide for the first time, evidence of Allee effects at nests level of V. germanica, which can have practical significance for the management on this invasive wasp.