Physiological Regulation Mechanisms Of Opius Caricivorae Fischer (Hymenoptera: Braconidae) On Its Host Liriomyza Sativae Blandchard (Diptera: Agromyzidae)

Opius caricivorae Fischer (Hymenoptera: Braconidae) is an important endoparasitoid of the vegetable leafminer, Liriomyza sativae Blandchard (Diptera: Agromyzidae) in China. The physiological interaction between the endoparasitoid and the leafminer was preliminarily studied. The morphology and ultrastructure of venom apparatus and venom component of the endoparasitoid, and the presence of virus-like particles and its distribution both in parasitoid and host were examined; the physiological effects of venom on the host were preliminarily evaluated. The results are summarized as follows:(1) The venom apparatus of O. caricivorae Fischer locating dorsally in the female abdomen belongs to Type I, and consists of a cone-shaped, tan coloured reservoir, seven transparent gland filaments, and a venom duct that ends at the base of the ovipositor. The TEM graphs of the venom apparatus shew that the gland filaments consist of an outer single layer of secretory cells, a layer of degenerated ectodermal cells and an inner intima which lines the lumen. Secretory cells contain a lot of organelles: vesicular organelles which secrete the components of venom, RERs (the most abandunt), mitochondria, Golgi bodies, vacuoles and nucleus. Secretory cells have strong secretary activity. The reservoir consists of muscular sheath, secretory cells, squamous cells and intima. There were vesicular organelles in the reservoir secretory cells, therefore the reservoir can not only reserves the venom but also secrete venom, but the morphology of vesicular organelles in the reservoir secretory cells differs from that in the gland filaments. The intima protrudes into lumen as many small protuberances and is coated by chitin.(2) There are two virus-like particles in O. caricivorae. One kind of spherical-shaped particles occurs both in the secretory cells of the gland filaments and the ovarial epithelial cells, approximately 50 nm in diameter. Another kind of rod-shaped particles occurs in the ovarial epithelial cells, about 300 nm long and 50 nm wide. They are not present on the surface of parasitoid eggs laid in the parasitized hosts, not in the venom reservoir, fat body and the tegument of parasitized host larvae.(3) The venom SDS-PAGE indicated that there were approximately 12 protein bands present, in which most of them are less than 100 kDa in molecular weights and only twobands are more than 100 kDa, with 20.1, 26 and 43.5 kDa bands the highest concentration, while in the Dufour's there were approximately 15 protein bands, in which four bands are less than 30 kDa, and the most abundant bands were 36.5, 42.7, 51.5, 77 and 121.4 kDa.(4) By choosing the right radiant intensity among 50, 100, 150 and 200 Gy γ-ray the livability of Opius caricivorae Fischer female wasps and eggs laid in the host was compared, indicating that 50 Gy dose could result in effective pseudoparasitism. The livability and fecundity of the parasitoid were not significantly affected and could normally parasitize their host larvae, whilst the development of their offspring embryos was completely inhibited.(5) Almost all of the wasp's eggs laid in the pseudoparasitized host were not encapsulated. Because pseudoparasitism can effectively eliminate the effect of larval secretion, we concluded that the parasitoid's venom (and probably virus-like particles) could play an important role in the suppression of host's encapsulation.(6) The development of the host larvae was not affected after pseudoparasitism as compared to the unparasitized host and parasitized host larvae. The duration of prepupa and the growth period of hosts were not significantly prolonged, and the body length and weight were not distinctly changed. However, some red flecks appeared on the tegument of host larvae about 7 hours after parasitism. The fat body became loose, released some transparent substance by 12 hours after pseudoparasitism, and then decomposed. These changes appeared earlier than normal host's.(7) The SDS-PAGE of hemolymph of normal, parasitized and pseudoparasitized hosts (3rd instar, mature larvae and pupae) indicated that there were no obvious differences among protein bands. The molecular weights of proteins were between 18 to 170 kDa. There were two proteins (31 and 32 kDa) in the larval hemolymph of normal, parasitized and pseudoparasitized hosts. At the same time, there was a 40 kDa protein in the hemolymph of pseudoparasitized 3rd instar larvae, mature larvae and parasitized mature larvae. A 28 kDa protein disappeared in the pseudoparasitized mature larvae and pupae. However a 42 kDa protein disappeared in the pseudoparasitized mature larvae and pupae. The SDS-PAGE of fat body suggested that there are no evident differences among protein bands. The content of 72 and 25.2 kDa proteins in the mature larvae and pupae is more...