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

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.

群聚效应基于互惠互利的种内相互作用，随着种群或群体中个体数量的增加，个体适应度和人均增长率也随之提升。当个体数量降至某一临界值以下时，群体或种群的成功率便会降低，这种现象常被称为群聚效应。在真社会性昆虫中，合作是其显著的标志性特征，因为同种个体对于成功执行不同的任务，如觅食和繁殖，至关重要。此类相互作用表明，社会性昆虫易受群聚效应的影响。本研究以黄蜂属黄蜂 Vespula germanica 为例，研究了其真社会性中的群聚效应。我们通过移除实验群体中的工蜂，实验性地探索了成分群聚效应及其潜在机制。我们测量了在不同工蜂数量比例变化下的产卵蜂数量、产卵蜂的体质指数以及巢穴中觅食者收集的蛋白质食物量。我们发现，工蜂数量的比例变化与产卵蜂数量的减少相关。此外，随着群体规模的扩大，蛋白质食物的收集量也随之增加。我们的研究结果突显了工蜂等级在真社会性物种成功中的重要性。我们首次提供了 V. germanica 在巢穴层面的群聚效应证据，这可能对这种入侵性黄蜂的管理具有实际意义。