Parasitism-induced Regulation On Host Development And Immune By Three Endoparasitoids

The important agricultural pest insects diamondback moth, Plutella xylostella and cotton bollworm, Helicoverpa armigera, and their effective natural enimies, namely Cotesia vestalis, Diadegma semicalausum and Campoletis chlorideae, were used to build the host-endoparasitoid system, they were Plutella xylostella-Cotesia vestalis, Plutella xylostella-Diadegma semiclausum and Helicoverpa armigera-Campoletis chorideae respectively. In the present study, the host body weight gain, protein content and phenoxidase activity of parasitized host were systemly campared in order to explore the regulative ability of endopatasitoids with different parasitic factors on host growth and development, nutritive metabolism, and immune reaction. Firstly, the reproductive systems of three endoparasitoids were studied to investigate their structures. Secondly, the effects of parasitization by three endoparasitoids on host body weight gain were investigated to demonstrate that the parasitic fators carried by endoparasitoid wasps played key roles. Thirdly, the changes of protein content of host insects after parasitization by three endoparasitoids may be related to the different strategy used by these three wasps. Finaly, to look for a quick detection of host parasitism, the host immune material phenoxidase activity were researched. The main results were as follows:1. The reproductive system of three parasitic waspsAt (25±1)℃under laboratory conditions, three kinds of mated female and male parasitic wasps were frozen for5min at-20℃, then the external genital organs and internal reproductive organs of three wasps were observed under optical microscope. The results showed that three parasitic wasps all have needle-shaped ovipositors, but the ovipositor of Cotesia vestalis was short and only one-third the length of other two ichneumonids. The female internal reproductive system consists of paired ovares each with multiple ovarioles. Each ovary is connected to a lateral oviduct, and the paired lateral oviducts meet medially in the common oviduct. The ovarian shape and sling length were different in three parasitic wasps. The three parasitic wasps all have paired venom glands and venom sac where venom is stored. The shape of venom sac of Cotesia vestalis is oval and transparent, but it is oblong oval in Diadegma semiclausum. The male reproductive system of three wasps have similar basic structure, but there were some in testicular size, shape of testis and the length of the spermaducts. The results showed that three kinds of female and male reproductive systems had similar basic structure; there are more similarities between Campoletis chorideae and Diadegma semiclausum.2. Parasitism-induced effects on host growth and development by three endoparasitoidsThe body weight of insect is an important index in measuring the growth of the host larvae. After parasitization of the2nd larvae of Helicoverpa armigera larvae or Plutella xylostella larvae, the body weight of each larva was recorded daily for six consecutive days. The host body weight and changes of instar had great differences in Helicoverpa armigera larvae parasitized by Campoletis chorideae and Plutella xylostella larvae parasitized by Cotesia vestalis or Diadegma semiclausum. The parasitized Helicoverpa armigera larvae did not significantly increase in body weight than that non-parasitized host larvae at the frist three days, and the development of parasitized Helicoverpa armigera larvae was constantly inhibited as compared with that of the non-parasitized inhibition of host development at the last three days, the body weight of non-parasitized host larvae was six times more than that of the parasitized Helicoverpa armigera larvae by Campoletis chorideae on the sixth day. Meanwhile, the developmental duration of parasitized Helicoverpa armigera larvae was distinctly prolonged and the development was completely inhibited in3rd instar when the non-parasitized host larvae had already pupated. The body weight of Plutella xylostella larvae parasitized by Cotesia vestalis or Diadegma semiclausum respectively were different. After parasitization by Cotesia vestalis, the body weight of the host larvae were consistently lower than that of non-parasitized host larvae, and the most significant difference appeared on the second day post parasitization. After parasitization by Diadegma semiclausum, the body weight of Plutella xylostella larvae was almost the same as control, but during the last parasitization stage, the parasitized host had greater weight than control. All results showed that the parasitized host larvae were distinctly prolonged in the developmental duration and eventually failed to pupate. In all three host-endoparasitoids system, the growth and development of Helicoverpa armigera larvae parasitized by Campoletis chorideae changed significantly, that means Campoletis chorideae can influence the hormone levels of parasitized Helicoverpa armigera larvae. The growth and development of Plutella xylostella larvae parsitized by two endoparsitoids also had different results; the inhibition of Cotesia vestalis on host was greater than Diadegma semiclausum becase of its wasp-associated factors.3. The changes of protein concentration in the hemolymph of host larvae parasitized by three parasitic wasps.Using the Bradford method to determine the protein contents in the hemolymph of host larvae parasitized by three parasitic wasps, the changes of protein contents were different in three host-endoparasitoid systems. The protein content in Helicoverpa armigera larvae parasitized by Campoletis chorideae was always significantly higher than that of the non-parasitized host, but the difference decreased gradually in later post parasitiziation stage. Also the protein profile was studied by SDS-PAGE. The results showed that the quantity of91Kda protein in parasitized host larvae increased significantly, maybe it is closely related to the growth and development of Campoletis chlorideae, or this protein can significantly inhibit the growth and development of parasitized host. The protein content in hemolymph of Plutella xylostella larvae parasitized by Cotesia vestalis was higher than that of the non-parasitized host on the third day after parasitizetion, but it was obviously lower than that of control on the fourth and fifth day after parasitization. The protein content in the hemolymph of host larvae parasitized by Diadegma semiclausum was higher than that of the non-parasitized host on the fourth day post parasitism, but it was lower than controls on the third and fifth day after parasitization. These results suggested that the protein synthesis was affected significantly in Helicoverpa armigera larvae parasitized by Campoletis chorideae, leading to more protein production in parasitized host than control. The protein synthesis and meatabolism were also affected by different wasp-associated factors carried by Cotesia vestalis or Diadegma semiclausum, which was the reason why different results observed from the same host Plutella xylostella larvae after parasiteization by two endoparasitoids.4. Rapid diagnosis of parasitism of host insectThe purpose of this study was to obtain a rapid diagnosis of parasitism of host insect by determination the phenoloxidase activity using absorbance value of 0-100min. Following parasitism of the2nd instar of Helicoverpa armigera larvae by Campoletis chorideae, or Plutella xylostella larvae parasitized by Cotesia vestalis or Diadegma semiclaus respectively. The ground whole host insect body was used to detect phenoloxidase activety. The results showed that the phenoloxidase activity changed differently between parasitized Helicoverpa armigera larvae and Plutella xylostella larvae. The PO activity of Helicoverpa armigera larvae was almost completely inhibited by parasitism of Campoletis chorideae, but the PO activity of Plutella xylostella host larvae was activated on the fourth and fifth day after parasitizetion by Cotesia vestalis. However, the degree of inhibition was almost0on second and fifth day post parasitizetion by Diadegma semiclausum. The PO activity changed differently because of the different wasp-associated factors. The results showed that the degree of inhibition of PO activety induced by Campoletis chorideae was higher than that by Cotesia vestalis or Diadegma semiclausum. Therefore, by testing the PO activity of ground Helicoverpa armigera larvae, we can judge the parasitism of cotton bollworm in the field.The PO activity of Plutella xylostella larvae parasitized by Oomyzus sokolowskii was determined by using the hemolymph supernatant of Plutella xylostella host larvae, which was different from the above method. The results showed that the PO activity of parasitized host larvae was only slightly inhibited compared with the control because Oomyzus sokolowskii is a larval-pupal endoparasitoid of diamondback moth, it belongs to obedient type other than regulator.