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

Abstract

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.

Body Size Shapes Caste Expression, and Cleptoparasitism Reduces Body Size in the Facultatively Eusocial Bees Megalopta (Hymenoptera: Halictidae)

“…When there is social competition for reproduction (see West-Eberhard 1978;Michener 1990;Wcislo 1997), any parasite-induced handicap could socially castrate its host, rendering it effectively sterile. Parasites that reduce body size or otherwise lower fecundity may be more common than previously thought (Shykoff and Schmid-Hempel 1991;Hughes et al 2003;Kudo et al 2004;Bouwma et al 2005). We predict that when these parasites reduce fecundity, either directly or through indirect behavioral effects, they will also promote the expression of worker behavior in their hosts (O'Donnell 1997 …”

Mating of Xenos vesparum (Rossi) (Strepsiptera, Insecta) revisited

“…6a). The 1st instar larvae leave their hosts on flowers and subsequently mount other foraging wasps, to reach new nests; alternatively, stylopized wasps could release these larvae directly on nests, where they enter a wasp larva to start a new parasite cycle (Hughes et al, 2003).…”

“…The primitively eusocial wasp Polistes dominulus is the prime host of Xenos vesparum (Stylopidae): in Tuscany more than 50% of nests may be infected (Hughes et al, 2003). The parasitized (stylopized) wasps become sterile (Strambi and Strambi, 1973).…”

Subtle effect of Xenos vesparum (Xenidae, Strepsiptera) on the reproductive apparatus of its male host: Parasite or parasitoid?

“…its reproductive death, even in a scenario when the parasite load is the lowest (i.e. one parasite), which is indeed the most common scenario in natural populations (Hughes et al, 2003(Hughes et al, , 2004.…”