The Physiological Regulations Of "Regulator" Or "Conformer" Parasitoids On Their Host Plutella Xylostella

In the present paper, we compared the phsiological effects of parasitization on diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), the most important crucifer pest worldwide, parasitized by two major endoparasitoids, the"regulator"Cotesia vestalis (Haliday) (Hymenoptera: Braconidae) or the"conformer"Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae). The major results are summarized as follows.1.The ongeny of Oomyzus sokolowskiiThe ongeny of Oomyzus sokolowskii was observed at 25±1℃, RH 60%-80%, photoperiod of 14 h light and 10 h dark with light intensity of 1000-1500lux, under lab conditions. The development period required for the embryo of O. sokolowskii is forty-four to forty-eight hours. After hatching, the larvae undergoes a obviously molting, it has two larval instars. The duration of larval stage was 6-8 d. The final larvae enters pre-pupal stage after ceasing feeding. The whole pupal stage was divided into three phases. The pupal period was 8-9 d. After emergence, the longevity of adult was only 4 days without feeding any food. The developmental time for O. sokolowskii from egg batch to adult emergence was 16-18 days.2.The effect of host instar on biological characters of Oomyzus sokolowskii, a larval-pupal parasitoid of Plutella xylostellaHost insect quality significantly influences the progeny fitness of endoparasitoid wasps. Choosing the suitable host instar and size will be useful for developing augmenting parasitoids as biological control agents. In present paper, we investigated the effects of host different instar and size on biological characters of Oomyzus sokolowskii (Kurdjumov), an important larval-pupal endoparasitoid of Plutella xylostella L. in the laboratory at (25±1)°C. The results showed that parasitoids developing in different host instars did not exhibit significant differences in development time, and adult longevity was almost the same. The proportion of male wasps that emerged from the late fourth instar hosts was significantly higher than for the late third instar larvae. In choice experiment, the wasp did not show any differences to four larval instars, the number of egg laid per host, indicating almost the same host suitability among different larval instars. However, the late third instar larvae was the most suitable host compared with the other instars for parasitoid, because the biggest wasp emerged from them. 3.Determination of free amino acids in the hemolymph of parasitized Plutella xylostella by ion chromatographyChanges in free amino acids were analysed in hemolymph of fourth instar larvae, prepupae and parasitized Plutella xylostella larvae by ion chromatography. Seventeen primary amino acids were detected among which histidine, proline and alanine were the predominant free amino acids at all stages. The concentration of total amino acids increased significantly with the age of larvae. However, the amount declined with the larvae entering the prepupal phase. This suggested that changes in amino acid metabolism occurred. After parasitization by Cotesia vestalis, the concentration of total amino acids increased significantly compared with synchronous non-parasitized controls. The parasitism resulted in increased levels of most of the amino acids. This parasitoid strongly redirected host protein and amino acid metabolisms to make the host nutritional environment suitable to its development. At the end of the immature development of this parasitoid, we observed a very significant decline in total amino acid contents. This suggested that C. vestalis used these amino acids effectively to ensure its larval development. The definition of a suitable artificial diet according to our results for in vitro mass production of this parasitoid in the future is necessary and helpful.4.The mechanisms of inerspecific competition between two endopatasitoids of diamondback mothIt can provide important theory basis for introduction of exotic natural enemies to control insect pests by establishing an ideal host-parasitoid model systems to clarify the mechanisms of interspecific competition between endoparasitoids. The interspecific competitive capacity between Oomyzus sokolowskii and Cotesia vestalis was studied using the 2nd instar larvae of Plutella xylostella as the host at 25℃in the laboratory. Different time intervals between parasitism and two parasitoid sequences were chosen. C. vestalis outcompeted O. sokolowskii from the multiparasitized host irrespective of whether it parasitized first or second. The one reason for this result was that C. vestalis can physically attack O. sokolowskii using advanced scleritized mandibles in multiparasitized host. Compared with C. vestlis, O. sokolowskii lack mandibles. The another reason for this result was that these two endoparasitoids regulated the host in different ways. C. vestalis has polydnaviruses, venom and teratocytes, whereas O. sokolowkii only has venom. The braconid has stronger regulatory ability on host than eulophid. In the presence of polydnaviruses and venom of C. vestalis, the duration of host larval stage was prolonged and could not pupate. Under this host physiological state, O. sokolowkii could not successfully develop. Furthermore, the high mortality of host parasitized by O. sokolowkii first lead to great reductions of eulophid.