Studies On The Structure Of Venom Apparatus Of Endoparasitoid Cotesia Plutellae (Hymenoptra: Braconidae) And The Regulatory Effects On The Host Plutella Xylostella By The Venom

The venom apparatus morphology and venom component of the endoparasitoid, Cotesia plutellae (Hymenoptera: Braconidae) and the venom functions on its host, Plutella xylosytella (Lepidoptera: Plutellidae) were studied. The results are summarized as follows:(1) The parasitoid venom apparatus comprises one venom reservoir and two gland filaments, locating dorsally in the female abdomen. The sections of TEM showed that the gland filaments consist of a single outer layer of secretory cells, a layer of degenerated ectodermal cells and an inner intima that lines the lumen. Secretory cells contain a lot of organelles: RERs, mitochondrions, Golgi bodies, lysosomes and vacuoles, in which vesicular organelle secretes the venom. The reservoir consists of a muscular sheath, a layer of squamous cells and intima. The photos of SEM showed that the intima protrudes into lumen of reservoir as many small protuberances and is coated by chitin. The reservoir keeps the venom that is secreted from filaments. The injection of venom is accomplished by muscular contraction of the reservoir during oviposition. The aging phenomenon of secretory cells was observed. Many myeloid bodies were present in the degenerated secretory cells. The morphology and ultrastructure of venom apparatus of another parasitoid of Plutella xylostella, Diadegma semiclausum (Hymenoptera: Ichneumonidae) was also studied for compare.(2) The SDS-PAGE showed that about 15 protein bands were detected in the parasitoid venom, of which most of them are lower than 100 KD in molecular weight, and seven protein bands even lower than 30 KD. The proteins of 121, 84.5, 53.8, 43, 47, 20.3, 14 and 10.6KD were the highest ones in content. Five similar protein bands (molecular weight around 120, 40 and 14 KD) were found in both venoms of Apis mellifera and C. plutellae. The electrophoresis profiles also showed that there were a lot of resembling bands detected in both parasitoid venom and calyx fluid, and several specific bands of their owns. No distinctive changes of venom content and protein component were found during the lifetime of female wasp.(3) When adult parasitoid females were irradiated with Y -ray at the dose from 50 Gy to 76200 Gy, their survival rate and fecundity are not significantly affected and could normally parasitize their host larvae whilst the embryos development of their offspring were completely inhibited, successfully resulting in the phenomenon of pseudoparasitism. On the contrary, high or low temperature treatments of newly parasitized host larvae were not able to affect the survival of wasp eggs. The 150Gy dose of Y -ray was therefore selected to cause the pseudoparasitism in all experiments of this study.(4) When host larvae were parasitized by irradiated female wasps (pseudoparasitized), the growth period of host larvae was obviously prolonged. When host larvae of second, third and early fourth instars were pseudoparasitized, they were not able to developed up to the prepupal stage and consequently died. But when the late fourth instar larvae were pseudoparasitized, a part of them could pupate into abnormal pupae and most of them retained in false prepupae before dead. The body weight and length of pseudoparasitized host larvae were obviously heavier and longer than those of parasitized and non-parasitized hosts, respectively. Some abnormal phenomena were observed in the growth of pseudoparasitized host larvae: their guts were intumescent, and many red spots were present on guts when they reached the fourth instar.(5) No significant differences in the rate of pupation and eclosion were observed between the fourth instar host larvae injected with venom and control (injected with saline solution), but the higher rate of abnormal pupae and moths than those of control was observed. The effect of injection doses was not obvious, suggesting that venom alone was limited in effects to cause developmental arrest.(6) The concentration of proteins in hemolymp...