Physiological Regulation Mechanisms Of Cotesia Plutellae (Kurdjumov) (Hymenoptera: Braconidae) On Its Host Diamondback Moth, Plutella Xylostella (Linnaeus) (Lepidoptera: Plutellidae)

Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) is one of major larval parasitoids of the diamondback moth (DBM), Plutella xylostella (Linnaeus)(), an important insect pest of crucifer vegetable crops. A better understanding of the physiological interactions between the parasitoid C. plutellae and its host P. xylostella will certainly enhance the biological control of the diamondback moth by this parasitoid. The characterization and physiological effects of the main parasitism factors, including teratocytes, polydnavirus (PDV) and venom, and their interactions in the system of C. plutellae--P. xylostella were studied in this paper. The physiological regulation mechanisms of C. plutellae on its host P. xylostella were preliminarily outlined. The major results are summarized as follows.1. Ultrastructure and development of C. plutellae teratocytesC. plutellae is an endoparasitoid, developing in the haemocoel of larval stages of the diamondback moth P. xylostella. Teratocytes were released from the serosal membrane during hatching of the parasitoid eggs into first instar larvae at 33~36h after oviposition at 25(?)癈; an average of 192 cells were released per embryo; the teratocytes increased in diameter from about 15.31(?.06) urn to 63.25 (?2.65) um, sometimes up to a size of 118.75um; the number of teratocytes declined during the course of parasitoid larval development. The photos of scanning electron microscopy (SEM) revealed that the surface of the teratocytes was covered with microvilli, which were much denser and longer on the 4th day than those on the 1st day. This implicated that they were actively involved in functions of absorption and secretion. The sections of transmission electron microscopy (TEM) revealed that the extensive dentritic ramification were developed on mature teratocyte nucleus, and the cells were endowed with the extensive endoplasmic reticulum, abundant mitochondria, large numbers of lysosome, and also the accumulation of glycogen granules and lipid droplets, especially in older teratocytes, thus providing circumstantial evidence for the occurrence of protein synthesis and secretion of teratocytes.2. Effects of host state and superparasitism on development of C.136plutellae larvae and their teratocytesThe effects of host state and superparasitism on the development of the parasitoid larvae and their teratocytes were studied. The results showed that the larvae of C. plutellae and their teratocytes developed faster in haemolymph of the hosts feeding on wild cabbage and Chinese cabbage than those on radish's. When the 4th instar host larvae were parasitized, the percentage of pseudoparasitism increased, and the developmental duration of parasitoid larvae were variable as compared those when the 2nd and 3rd instar larvae parasitized. After superparasitism, more numbers of teratocytes were present in host haemolymph with the diameter much smaller as compared with normal (parasitized only once). Other factors, for example, the rearing temperature and pathogens, also had effect on the development of teratocytes and parasitoid larvae. The numbers of teratocytes decreased and the activity was reduced in the parasitized host larvae starved for a period of time, and the development of parasitoid was also arrested at the same time. All of these results revealed that there is a positive interaction relationship among the development of host, parasitoid and teratocytes.3. Characterization and physiological effects of C. plutellae polydnavirus on host larvae of P. xylostellaThe polydnavirus of C. plutellae was characterized and its physiological effects on the host larvae, P. xylostella were studied . The results showed that the virion of polydnaviruses (PDVs) in the calyx region of female ovary had a tail and multiple nucleocapsids (up to 16) enveloped; the nucleocapsid measured 40 -168 nm in length and 39 - 40 nm in diameter; PDVs replicated only in calyx cells that underwent lysis after replication completed; the calyx fluid was injected...