Parasitism Preference And Offspring Performance As Affected By Host Species And Captive Breeding In Meteorus Pulchricornis

Meteorus pulchricornis (Wesmael) is a solitary endoparasitoid in Euphorinae (Hymenoptera:Braconidae). Its host range is broad, including most macro-Lepidopterous moth larvae such as the gypsy moth, Lymanstria dispar (L.), the cotton bollworm, Helicoverpa armigera (Hiibner), and the beet armyworm, Spodoptera exigua (Hiibner). So far, many researches have been set concerning about the choice decision in M. pulchricornis among different instars of host larvae, but the studies on different host species are hardly exist. In this article, based on controlling the influence from host size and instar, the choosing behaviors have been observed between Spodoptera litura and Mythimna separate, and the performance of offspring wasp from these hosts have also been recorded and analyzed synthetically. Further more, preliminary observations about the parasitic behaviors due to mass rearing inside artificially were carried out. Here are the main results and conclusions.1. The predication from the optimal diet model of classical foraging theory is that female wasps prefer to lay eggs in most suitable hosts for development of their offspring. Meteorus pulchricornis and its natural hosts Spodoptera litura and Mythimna separate larvae were used for the testing experiment. To control for confounding effects of host body size and age, a female parasitoid was exposed to larvae of the two species as hosts that were similar in body size and age each at three levels. The result showed that M. pulchricornis preferred M. separate to S. litura in terms of the number of ovipositor drilling and parasitization rate as measured by pupation rate. However, the offspring parasitoids from S. litura were larger than those from M. separate as measured by weight of cocoons and hind tibia length of emerged adults. Longevity of adult parasitoids from two host species were not significantly different. This should be some different from the predication, and we had a discussion as to discrepancy between oviposition preference and offspring developmental performance at last.2. Quality degeneration is a common problem in massbreeding natural enemies frobiological control. The experiment wass made to compare three types of parasitoids in parasitization selection and development performances of their offspring, which included parasitoids from the field (WF), from captive breeding stock (BI,> 14 generations), and from the field-recovered population of breeding parasitoids (RO). The result shows that RO was better than WF and BI in the performance of fecundity and offspring development. The number of offspring wasps from RO was 23.6% and 19.3% higher than those from WF and BI respectively, which up to 32.9 offsprings by each female wasp, and ii also had the longest time span of ovipsition (nine days). The rate of cocoon formation from RO (79.2%) was 19.3% higher than BI, and rate of emergence from WF (86.1%) and RO (77.2%) were 36.9% and 22.7% higher than BI respectively. The hind tibia length from WF was 10.9% and 11.4% longer than RO and BI respectively. But the longevity from three different groups of wasps has no obvious difference. In brief, the results shows that, the situation of wasps being breeding indoors for over 14 generation would be get worse, and the way of rejuvenesce by releasing in wild field works and could help us keeping wasps better.