Effects of Helicoverpa armigera (Noctuidae, Lepidoptera) host stages on some developmental parameters of the uniparental endoparasitoid Meteorus pulchricornis (Braconidae, Hymenoptera)

A single choice test was performed to examine developmental strategies in the uniparental endoparasitoid Meteorus pulchricornis and its host, the cotton bollworm Helicoverpa armigera. The results support the dome-shaped model in which the fitness functions are 'dome-shaped' relative to size (and age) of host at parasitism. Older and, hence, larger host larvae were simply not better hosts for the developing parasitoids. Although parasitoid size (measured as cocoon weight and adult hind tibia length) was positively correlated with host instars at parasitism, parasitoids developing in larger hosts (L-5 and L-6) suffered much higher mortality than conspecifics developing in smaller hosts (L-2-L-4). Furthermore, egg-to-adult development time in M. pulchricornis was significantly longer in older host larvae (L-4-L-6) than in the younger. Performance of M. pulchricornis, as indicated by fitness-related traits, strongly suggests that the L-3 host is the most suitable for survival, growth and development of the parasitoid, followed by both L-2 and L-4 hosts; whereas, L-1, L-5 and L-6 are the least favourable hosts. The oviposition tendency of M. pulchricornis, represented by parasitism level, was not perfectly consistent with the performance of the offspring; L-2-L-4 hosts, although with the same parasitism level, had offspring parasitoids with differences in fitness-related performance. Larval development in Helicoverpa armigera was usually suspended, but occasionally advanced, in the final instar.