The invasive yellow-legged hornet Vespa velutina nigrithorax was accidentally introduced in Europe in the early 2000s. As is the case in colonies of other wasp and hornet species, V. velutina colonies are known to produce sexuals (males and new queens) at the end of the summer. We show that early-stage colonies in French populations frequently produce males well before the usual reproductive period. The vast majority of the males produced are diploid, which is consistent with the loss of genetic diversity previously reported in introduced populations in France. Since males do not participate in colony activities, the production of early diploid males at the expense of workers is expected to hamper colony growth and, ultimately, decrease the expansion of the species in its invasive range in Europe.

Invasive social insect populations that have been introduced to a new environment through a limited number of introduction events generally exhibit reduced variability in their chemical signatures (cuticular hydrocarbons) compared to native populations of the same species. The reduced variability in these major recognition cues could be caused by a reduction of genetic diversity due to a genetic bottleneck. This hypothesis was tested in an inbred European population of the invasive hornet Vespa velutina nigrithorax. Our results show that, in spite of the limited amount of genetic diversity present in the European population, the chemical signatures of individuals were highly heterogeneous according to their caste, sex, and colony origin. In queens, some specific saturated and unsaturated hydrocarbons were identified. These results suggest that epigenetic and/or environmental factors could play a role in modifying cuticular hydrocarbon profiles in this introduced hornet population despite the observed reduction of genetic diversity.

International audienceThe yellow-legged hornet, Vespa velutina nigrithorax, was accidentally introduced from China to southwestern France in 2004 (Haxaire et al. 2006). The species is currently colonizing France and neighboring countries (Spain, Portugal, Belgium, and Italy) (Darrouzet and Gévar 2012; Monceau et al. 2013). V. velutina is a pest in France because it preys upon domestic honeybees, Apis mellifera. Beekeeping operations are directly affected by this predation, with some beekeepers reporting colony losses (Darrouzet and Gévar 2012; Monceau et al. 2013).While many factors may play a role in the successful establishment of an invasive species, research has focused on the effects of parasites (Prenter et al. 2004). It has previously been suggested that invasive species are subject to less pressure from parasites than are sympatric native species because invasive species leave their parasites behind when they invade new habitats (enemy release hypothesis). They can thus allocate more resources to gr ..