Prevalence of the parasite Strepsiptera in Polistes as detected by dissection of immatures

Though the paper wasp genus, Polistes, is well studied, we know little of the incidence of parasitism in this group. Here we present details of 45 nest dissections for 4 species: P. dominulus (Christ), P. gallicus (L.), P. stabilinus Richards and P. carnifex (F.) to detail levels of parasitism of colony members by the obligate parasitic group of insects, the Strepsiptera. All 4 species showed evidence of parasitism among immature members. For 3 species, more than 50% of inspected nests were parasitized and the levels of parasitism among brood (larvae and pupae) was very high and did not differ significantly between parasitized nests. One species, P. stabilinus, suffered very low levels of parasitism, which may be related to its habitat choice. The number of parasites per host was positively related to the proportion of infected brood (parasite prevalence) and in some cases reached phenomenally high levels, which casts doubt on previously assumed mechanisms of infection for nest-making Hymenoptera, i.e. phoresy. We also document cases of egg parasitism and encapsulation in Polistes nests. Our data show that parasitism levels greatly varied among areas. Finally, the recent debate on the competitive advantage of P. dominulus in its introduced range, USA, has credited an absence of strepsipteran parasites of this species in facilitating its spread. For the first time, we document levels of parasitism for this species in its nature P range and this would appear to corroborate previous claims. We place our work in the context of other studies of parasitism of social insects and posit that the genus Polistes may have much to offer to this field.