| The characteristics and effects of the venom of Cotesia plutellae (Hymenoptera: Braconidae) and the immature development of this parasitoid in the host, Plutella xylostella (Linnaeus) were primarily studied. The results are summarized as follows:1 Venom protein components of Cotesia plutellaeEach venom reservoir contained about 0.169 μg proteins. Analysis of the 12 % SDS-PAGE profile revealed the presence of 20 protein bands with molecular weight ranging from 7.98 to 301.6 kDa, i.e., 301.61, 183.18, 134.65,112.31, 82.34, 70.46, 63.76, 60.62, 46.11, 45.06, 42.27, 31.93, 27.73,26.36, 24.23,21.78, 15.27, 12.89, 10.21 and 7.98 kDa, of which nine protein bands including 112.31, 82.34, 63.76, 60.62, 45.061, 27.73, 26.36, 24.23 and 10.21 kDa, were relatively abundant.2 Enzyme analysis of venom of Cotesia plutellaeActivities of four enzymes were detected in the venom from C. pltellae, including acid phosphatase (ACP), alkaline phosphatase (ALP), esterase (EST) and trehalase (TRE). From emergence, the ALP was present at a stable activity level. Enhanced activities of ACP and TRE were detected and the highest activity was present two days after. While the EST activity decreased and reached to the lowest level 6 days after and then increased.3 Effects of venom/calyx fluid from Cotesia plutellae on the hemocytes of its host Plutella xylostella in vitroVenom from C. plutellae displayed high activities toward the spreading of plasmatocytes of P. xylostella at the early time of the incubation period, and the inhibition was more severe as the concentration of venom increased. However, most of ever inhibited hemocytes spread normally after incubated for 4 h. No effects were found toward granular cells from the host. Additionally, the venom from C. plutellae had no lethal effects on hemocytes of P. xylostella. In contrast, when incubated with different concentrations of calyx fluids, the spreading of some hemocytes wereinhibited, some began to disintegrate, and some were badly damaged with only nucleus left. After 4 h, the majority of hemocytes died. The same results were observed when incubated in the calyx fluid together with venom. These results show that calyx fluids from C.plutellae play main roles in the suppression of the host immune system and venoms from C. plutellae only synergize the effect of calyx fluid or polydnavirus.4 Development of venom apparatus of Cotesia plutellae and its relationship with the oogenesisWhen fed with honey, the length of venom glands from C. plutellae had no significant changes with the development of female wasps, while more changes were observed on venom reservoir volume and venom protein content. When emergence, venom reservoir was small with only 0.06231 ± 0.0007ug protein each reservoir. Both venom reservoir volume and protein content increased one day after, and reached to the highest level with 0.1681 ± 0.0013 \ig protein two days after. When not feeding, the development of venom reservoir was relatively slow and the volume was much smaller with only 0.152 ± 0.0012 ug protein each reservoir. And their life was shortened to two days. In contrast, mating had no significant effects on the venom apparatus development.When feeding and mating, the length of venom glands from C. plutellae showed negative correlation with the number of immature eggs from the ovary while positive correlations were observed between the number of mature eggs and the venom reservoir volume as well as venom protein content. And linear relations were found between the parts of venom apparatus from female C. plutellae.5 Observation on morphology of eggs, larvae and pupae of Cotesia plutellaeOur results showed that the egg stage of C. plutellae last 2 days. Before hatching, obvious segments, the gut and a pair of sclerotized mandibles were observed clearly. The larvae appeared to have 3 instars, in which the first, second and third instar last 2, 5 and 1 days, respectively. The first instar larvae were charactered with a larger head, a pair of reaphook-like mandibles and a tail. The mandibles disappeared and the tail was replaced by a vesicle at the second instar. And the vesicle would shrink back to thelarvae at the end of the second instar and the tracheal system completely formed. The third instar larve came out of the host body and began to extrude filaments to form a cocoon. The prepupae were little yellow with a pair of orange red compound eyes distinct. The midgut and hindgut began to fuse and the meconium was excluded. The pupae were bright yellow with three dorsal ocelli obvious, and the antennae, legs and wings were transparent with no colour and adhered to the body. The exuviae of the third instar larvae remained attached to the abdominal apex.
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