Abstract
In social wasps, female lifespan depends on caste and colony tasks: workers usually live a few weeks while queens as long as 1 year. Polistes dominula paper wasps infected by the strepsipteran parasite Xenos vesparum avoid all colony tasks, cluster on vegetation where parasite dispersal and mating occur, hibernate and infect the next generation of wasp larvae. Here, we compared the survival rate of infected and uninfected wasp workers. Workers’ survival was significantly affected by parasite sex: two-third of workers parasitized by a X. vesparum female survived and overwintered like future queens did, while all workers infected by a X. vesparum male died during the summer, like uninfected workers that we used as controls. We measured a set of host and parasite traits possibly associated with the observed lifespan extension. Infected overwintering workers had larger fat bodies than infected workers that died in the summer, but they had similar body size and ovary development. Furthermore, we recorded a positive correlation between parasite and host body sizes. We hypothesize that the manipulation of worker’s longevity operated by X. vesparum enhances parasite’s fitness: if workers infected by a female overwinter, they can spread infective parasite larvae in the spring like parasitized gynes do, thus contributing to parasite transmission.
Highlights
The flexible caste determination mechanism of Polistes dominula[22,23] is exploited by the strepsipteran Xenos vesparum (Xenidae), a parasitic castrator that usurps the host reproductive resources to complete its life c ycle[24]
Survival rates differed among the four groups of wasps that we analysed: workers parasitized by a X. vesparum female or by a male, non-parasitized workers and non-parasitized gynes, collected 3 months later, in October, when gynes form pre-hibernating aggregations (Table 1)
In the present study we provide the first evidence that the strepsipteran X. vesparum extends the lifespan of P. dominula workers, which can overwinter like future queens
Summary
The flexible caste determination mechanism of Polistes dominula[22,23] is exploited by the strepsipteran Xenos vesparum (Xenidae), a parasitic castrator that usurps the host reproductive resources to complete its life c ycle[24]. Parasitized P. dominula females, the primary host[25,26], do not develop ovaries, desert the colony early in the season without performing any social task[27] and forage on selected plants, rich of extra-floral nectaries secreting immune-stimulant compounds[28,29]. They form aberrant summer aggregations, where parasite mating o ccurs[30], and may overwinter in sheltered sites with future queens[31]. Theoretical and empirical data[3,24] suggest that parasitic castrators often grow to a body size that allows them to maximize their fitness without compromising host longevity
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