The Polistes war: weak immune function in the invasive P. dominulus relative to the native P. fuscatus

Invasive species are of growing ecological concern, in part because of conflicts arising with native congeners. The European paper wasp Polistes dominulus was first introduced to North America in the 1970s, and may be displacing at least one native species, P. fuscatus. Previous reports indicate that in native territories over half of P. dominulus colonies are infected by Strepsipteran parasites, which decrease host fitness. In North America, P. fuscatus are parasitized to a lesser degree (approximately one-third), but no infected colonies of invasive P. dominulus have been reported. Because immune function is an indicator of susceptibility to parasitism, we quantified activated levels of immune function by measuring the encapsulation response and phenoloxidase activity and then compared these levels between species. Counterintuitively, our results indicate that P. dominulus has lower levels of both mechanisms of immunity. Additionally, P. dominulus displayed less self-grooming activity than P. fuscatus. We briefly discuss possible immunological explanations for this invasion success, including the selective expression of low immunocompetence.