Physiological Regulation Mechanisms Of Cotesia Plutellae (Kurdjumov) (Hymenoptera: Braconidae) Teratocytes 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) (Lepidoptera: Plutellidae), an important insect pest of crucifer vegetable crops. The characterization of the major parasitoid-associated factor—teratocytes and their physiological effects on host and parasitoid larvae in the system of C. plutellae--P xylostella were studied in this paper. The physiological regulation of C. plutellae on its host P. xylostella were preliminarily outlined. The major results are summarized as follows.1. Immunosuppression of host immunity by Cotesia plutellae teratocytesThe activity of phenoloxidase (PO) of host larval hemolymph varied with the change of time. In general, it was evidently higher of the parasitized host larval hemolymph than that of unparasitized host hemolymph treated with PTU, but obviously lower than that of unparasitized host hemolymph without PTU. The activity of phenoloxidase (PO) of host larval hemolymph was related to the inhibition effect by teratocytes. When teratocytes became matured, their ability of immunosuppression on PO activity ascended, and then descended while they disaggregated.Incubated with haemocytes, more than half of the teratocytes were encapsulated by haemocytes in one hour, the percentage of encapsulation reached to 100% in six hours, and teratocytes were killed and reduced to 20% in numbers in 12 hours. Wile incubated with haemocytes, the percentage of encapsulation of the parasitoid larvae by haemocytes was only 4.2% in one hour and up to 49.2% in 12 hours, and the haemocytes were still active and did not reduce much in numbers. When teratocytes and parasitoid larvae incubated together with haemocytes, the percentage of encapsulation of teratocytes and parasitoid larvae reduced, The reason for this is probably that teratocytes and parasitoid larvae could activate each other, resist encapsulation, and then acceletate the disaggregation of haemocytes.2. Regulation and utilization of host nutrition by Cotesia plutellaeThe feeding, development and nutrition metabolism of the host P. xylostella were changed dramatically after parasitized by the endoparasitoid C. plutellae with the impact of different parasitoid-associated factors and the growth of parasitoid larvae. Teratocytes as one factor play an important role. By comparing the changes in proteins of parasitized host and unparasitized host hemolymph and the incubation mediums of 2nd instar parasitoid larvae using these two hemolymph in vitro, we found that the protein concentration of the parasitized host hemolymph was only slightly (not significantly) lower than that of the unparasitized host, but the protein concentration of the incubation medium using unparasitized host hemolymph was significantly lower than that of parasitized host, indicating that the teratocytes have the ability to secrete proteins. The body weight of parasitized host was greater than that of unparasitized host while the reverse is true for the weight of fat body in the late stage of parasitization. Microscopy observations revealed that the moniliform fat body was broken into granules induced by teratocytes which attach the fat body tissue;correspondingly the soluble protein and lipid concentration of fat body decreased rapidly, much lower as compared to those of unparasitized host. At the same time parasitoid larva grows rapidly, its midgut becomes matured and absorbed the large amount of the host nutrients, the esterase activity of the midgut of parasitoid larvae increased accordingly and its amount of total lipid of the parasitoid larva increased up to its highest level. In conclusion, in the late stage of parasitization the parasitoid larva robbed the host nutrients for its own development and growth with the help of teratocytes. 3. Secretory function of Cotesia plutellae teratocytes and parasitoid larvaeProtein component analysis of host larval hemolymph showed that there were no evident differences between parasitized and unparasitized host larval hemolymph. The host larvae parasitized in five days and the unparasitized host larvae one day before pupation had more protein bands. There were 72KDa and 92KDa proteins in parasitized host hemolymph as well as in unparasitized host hemolymph, but only parasitized host had 62KDa protein. The 92KDa protein existed in the incubation medium of the different-age teratocytes. There were abundant 62KDa protein in the incubation medium of parasitoid larvae.The similar results were obtained from the collagenase zymography: there were gelatinase A and B in both parasitized and unparasitized host hemolymph;a 62KDaproteinase. which was the active format of gelatinase A, presented in parasitized host hemolymph in four days after parasitization;the incubation medium of teratocytes had abundant gelatinase A and B;a 62KDa proteinase which was the main proteinase in the incubation medium of parasitoid larvae appeared in the incubation medium of teratocytes from host larvae in five days after parasitization.