EFFECT OF PARASITIZATION BY THE PUPAL ENDOPARISITOID,PTEROMALUS PUPARUM (HYMENOPTERA: PTEROMALIDAE) ON HUMORAL IMMUNE REACTIONS OF PIERIS RAPAE (LEPIDOPETERA: PIERIDAE)*

Abstract Studies on the effect of parasitization by the endoparasitoid on host humoral immune reactions are carried out with the pupal endoparisitic wasp, Pteromalus puparum, and its host, Pieris rapae. Phenoloxidase (PO) activity of parasitized hosts hemolymph increased significantly at 12 h, day four and day five after parasitization. Hem‐agglutination activity of parasitized hosts hemolymph was always higher than that of wounded and unparasitized ones. Moreover, antibacterial activity of parasitized hosts hemolymph became more and more stronger, whilst wounded and unparasitized pupae only owned a weak antibacterial activity. It suggested that activities of humoral immune factors of Pieris rapae could be influenced to some degrees by P. puparum.     

分离自苏云金芽胞杆菌的首例细菌乌头酸异构酶TbrA的酶学性质研究

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The impact of co-infection by a nucleopolyhedrovirus and the endoparasitoid Microplitis pallidipes on the total hemocyte count and composition in larval beet armyworm,Spodoptera exigua

The physiological effects of nucleopolyhedrovirus (NPV) infection and parasitism by Microplitis pallidipes (Hymenoptera: Braconidae) on the hemocytes of Spodoptera exigua (Lepidoptera: Noctuidae) larvae were examined. We found that compared to healthy (control) larvae, the total hemocyte count (THC) and granulocyte count in parasitized larvae increased 1 day after parasitization and then decreased, while the plasmatocyte count was not significantly affected for the first 5 days but was significantly enhanced on day 6 after parasitization. In parasitized + infected larvae, both the THC and granulocyte counts began be lower from day 1 compared to parasitized larvae, while the plasmatocyte count was generally lower than in parasitized larvae. Compared to the control, THC, and granulocyte counts of virus-infected larvae were higher 1 day after infection. Compared to that in virus-infected larvae, THC and granulocyte counts in parasitized + infected larvae began to decrease from day 1 while the plasmatocyte count generally decreased. We concluded that the host immune response of cell communities to parasitization by M. pallidipes was elicited during the development of the parasitoid egg, but that immune response was inhibited during larval development of parasitoids in the host body. Meanwhile, we found that NPV infection impeded the regulatory effect of M. pallidipes on host cellular immune responses, and parasitization by M. pallidipes similarly inhibited the host cellular immune response caused by NPV infection.     

CLP gene family,a new gene family of Cotesia vestalis bracovirus inhibits melanization of Plutella xylostella hemolymph

Polydnaviruses (PDVs) are obligatory symbionts of parasitoid wasps and play an important role in suppressing host immune defenses. Although PDV genes that inhibit host melanization are known in Microplitis bracovirus, the functional homologs in Cotesia bracoviruses remain unknown. Here, we find that Cotesia vestalis bracovirus (CvBV) can inhibit hemolymph melanization of its host, Plutella xylostella larvae, during the early stages of parasitization, and that overexpression of highly expressed CvBV genes reduced host phenoloxidase activity. Furthermore, CvBV-7-1 in particular reduced host phenoloxidase activity within 12 h, and the injection of anti-CvBV-7-1 antibody increased the melanization of parasitized host larvae. Further analyses showed that CvBV-7-1 and three homologs from other Cotesia bracoviruses possessed a C-terminal leucine/isoleucine-rich region and had a similar function in inhibiting melanization. Therefore, a new family of bracovirus genes was proposed and named as C -terminal L eucine/isoleucine-rich P rotein (CLP). Ectopic expression of CvBV-7-1 in Drosophila hemocytes increased susceptibility to bacterial repression of melanization and reduced the melanotic encapsulation of parasitized D. melanogaster by the parasitoid Leptopilina boulardi. The formation rate of wasp pupae and the eclosion rate of C. vestalis were affected when the function of CvBV-7-1 was blocked. Our findings suggest that CLP genes from Cotesia bracoviruses encoded proteins that contain a C-terminal leucine/isoleucine-rich region and function as melanization inhibitors during the early stage of parasitization, which is important for successful parasitization.     

Bionomic notes on Pachysomoides sp. (Hymenoptera: Ichneumonidae), a parasitoid of the Neotropical social wasp Polistes satan Bequaert (Hymenoptera: Vespidae)

Although most polistine wasp species are found in the Neotropical region, mainly in Brazil, only a very limited number of South American parasitoids or parasites are known to exist. We assessed the frequency of a hymenopterous parasitoid, Pachysomoides sp. (Ichneumonidae, Cryptinae), in the nests of the Brazilian independent‐founding wasp Polistes satan and compared the rates of the parasitization of P. satan by Pachysomoides sp. between the dry (winter) and wet (summer) seasons. Pachysomoides sp. larvae were seen to feed on P. satan pupa and were found in both the upper and lower parts of the host pupal cell (ca. 10 individuals in each host pupal cell). Approximately one‐third of the pupal cells in the P. satan colonies were parasitized in the dry season, whereas there were no parasitized pupal cells in the wet season. Consequently, the rates of parasitization by Pachysomoides sp. were significantly greater during the dry season than during the wet season due to unknown reasons.     

Survival of the parasitoidEncarsia formosa after treatment of parasitized greenhouse whitefly larvae with fungal spores ofAschersonia aleyrodis

The interaction between the entomopathogenic fungusAschersonia aleyrodis and the parasitoidEncarsia formosa on greenhouse whitefly as a host organism was studied, in particular, the survival of the parasitoid after treatment of parasitized hosts with fungal spores. The mean number of parasitized black pupae per parasitoid produced at 25°C was significantly reduced after spore treatment in the first three days following parasitization. Spore treatment four, seven or ten days after parasitization resulted in a mean number of parasitized pupae not significantly different from the number of black pupae in the control. The rather sudden change from low to high survival of parasitized hosts when treated with spores four days after parasitization in spite of high numbers of infected unparasitized larvae, coincided with the hatching of the parasitoid larva from the egg inside the host. Possible reasons for this decrease in susceptibility to infection after parasitoid egg hatch, such as induced changes in host cuticle or haemolymph, are discussed. Parasitoids emerged from treated hosts did not show differences in reproduction compared with parasitoids emerging from untreated hosts. Both natural enemeies of whitefly are compatible to a great extent.     

Cytotoxic effects of parasitism and application of venom from the endoparasitoid Pimpla turionellae on hemocytes of the host Galleria mellonella

In parasitoid species devoid of polydnaviruses and virus‐like particles, venom appears to play a major role in suppression of host immunity. Venom from the pupal endoparasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) has previously been shown to contain a mixture of biologically active components, which display potent paralytic, cytotoxic, and cytolytic effects toward lepidopteran and dipteran hosts. The current study was undertaken to investigate if parasitism and/or envenomation by P. turionellae affects the frequency of apoptotic and necrotic hemocytes, hemocyte viability and mitotic indices in Galleria mellonella L. (Lepidoptera: Pyralidae) pupae and larvae. Our study indicates that parasitism and experimental envenomation of G. mellonella by P. turionellae resulted in markedly different effects on the ratio of apoptotic hemocytes circulating in hemolymph depending on the host developmental stages. The ratio of early and late apoptotic hemocytes increased in G. mellonella pupae and larvae upon parasitization and at high doses of venom when compared to untreated, null and Phosphate Buffered Saline (PBS) injected controls. In contrast, an increase in necrotic hemocytes was only observed in parasitized pupae at 24 h and no difference was observed in larvae. The lowest hemocyte viability values were observed with pupae as 69.87%, 69.80%, and 72.47% at 4, 8, and 24 h post‐parasitism. The ratio of mitotic hemocytes also decreased in pupae and larvae upon parasitization and at high doses of venom. Staining of hemocytes with annexin V‐FITC revealed green fluorescent ‘halos’ along the plasma membranes of venom treated cells within 15 min following exposure to venom. By 1 h post‐venom – treatment, the majority of hemocytes displayed binding of this probe, indicative of early stage apoptosis. These same hemocytes also displayed a loss of plasma membrane integrity at the same time points as evidenced by accumulation of propidium iodide in nuclei.     

Venom of Pteromalus puparum (Hymenoptera: Pteromalidae) induced endocrine changes in the hemolymph of its host,Pieris rapae (Lepidoptera: Pieridae)

Pteromalus puparum is a predominant endoparasitoid wasp of Pieris rapae. Its venom is the only active factor injected into host associated with oviposition. In this report, we explored whether the venom alone from this wasp affects the endocrine system of its host or not. We monitored the changes of hemolymph juvenile hormone (JH; only JH III detected), ecdysteroid, and juvenile hormone esterase activity (JHE) over 72 h in parasitized and venom‐microinjected P. rapae pupae. Non‐parasitized and PBS‐microinjected P. rapae served as controls. Results showed that JH titers were significantly higher in parasitized and venom‐microinjected pupae than that in control pupae during 24 to 72 h. After 12 h, JH titers were significantly promoted by parasitization and venom microinjection. JHE activities of non‐parasitized and PBS‐microinjected pupae were significantly higher than that of parasitized and venom‐microinjected pupae, which was with a peak at 12 h (parasitized pupae) or 24 h (venom‐microinjected pupae) during 6 to 48 and 12 to 36 h, respectively. The hemolymph titers of ecdysteroid in non‐parasitized and PBS‐microinjected pupae increased rapidly during 12 to 36 h with a peak at 36 h, and were higher than treatments before 48 h, while presenting a significant difference at 24 to 48 h between the treatments and controls. The results demonstrate that venom alone of this parasitoid wasp can disrupt its host's endocrine system. © 2009 Wiley Periodicals, Inc.