Production of Early Diploid Males by European Colonies of the Invasive Hornet Vespa velutina nigrithorax

Abstract

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.

Fig 1. Flow cytometric DNA histogram of diploid female (a), haploid male (b) and diploid male (c).

Each histogram shows the nuclear frequency with regard to DNA content for the head of a single individual. The first peak corresponds to ploidy level, the second peak to nuclei with a double DNA content and the third peak to polyploid nuclei. In haploid males, the second peak (2C) corresponds to nuclei from mandibular muscles where cells are diploids.