Reduction of larval resistance and adult reproductive capacity in Spodoptera littoralis at different degrees of superparasitization by Microplitis rufiventris

The solitary endoparasitoid, Microplitis rufiventris Kok, attacks and can develop in the first three instars of Spodoptera littoralis (Boisd.) larvae with preference for third-instar. We used the last three instars to show the effect of increasing superparasitization on host resistance and reproductive capacity of surviving moths of S. littoralis that had been parasitized during their newly moulted fourth, fifth and sixth instar larvae. The degree of resistance of late instars and reproductive capacity of surviving moths varied significantly as a function of both, the virulence factors (number of wasp eggs, venom and polydnavirus) and size of host instars. Increasing number of parasitism events overcame resistance in larger host instars. The host survival was increased with the host instar and decreased with the number of ovipositions, while the chances that at least one wasp emerges follow a reverse pattern. When the survived parasitized hosts were able to pupate, parasitism usually reduced their weight, but sometimes the host pupal weight was increased. Furthermore, for surviving hosts, the weight of egg masses produced in female moths, decreased with increasing superparasitization, that is, the number of ovipositions during their larval stage. The 'threshold' number of parasitoid eggs, which allows the development of host, accounts for three parasitoid eggs in the fourth and fifth host instar and five parasitoid eggs in the sixth instar. The survived parasitized hosts (L4-L6) exhibited fitness-related costs in terms of smaller size and lower reproductive output.