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At least 1,225 records · Page 68Linked to original sources
PubMed2000

Relationships between polydnavirus gene expression and host range of the parasitoid wasp Campoletis sonorensis.

To evaluate the relationship between immune suppression and host range six lepidopteran species were parasitized by the ichneumonid parasitoid Campoletis sonorensis. Parasitism inhibited the growth of permissive hosts (Heliothis virescens, Helicoverpa zea, and Trichoplusia ni), whereas growth of semi-permissive (Spodoptera exigua, Agrotis ipsilon) and non-permissive hosts (Manduca sexta) was not significantly affected. The 29-36 kDa ovarian protein (OP), responsible for transient immunosuppression in the permissive host H. virescens, bound to and was endocytosed by hemocytes of permissive and non-permissive hosts. Expression of the cysteine-rich polydnavirus gene, VHv1.4, was detected in all the hosts, but declined only in semi- and non-permissive hosts at later times after parasitization. The VHv1.4 protein bound to hemocytes of permissive and semi-permissive hosts, but did not bind to hemocytes of the non-permissive host, M. sexta. Melanization of larval hemolymph was severely inhibited by parasitism in permissive hosts, but was unaffected in M. sexta. In the semi-permissive host, A. ipsilon, hemolymph melanization was transiently inhibited while viral genes were expressed. In conclusion, C. sonorensis OP transiently inhibits encapsulation in all hosts that were tested. The host range of C. sonorensis seems to be determined by whether or not the C. sonorensis ichnovirus (CsIV) is able to establish persistent infections of parasitized larvae to provide long-term suppression of host immunity.

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PubMed2002

The ectoparasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) differentially affects cells mediating the immune response of its flesh fly host, Sarcophaga bullata Parker (Diptera: Sarcophagidae).

In this study, we examined cellular immune responses in the flesh fly, Sarcophaga bullata, when parasitized by the ectoparasitoid Nasonia vitripennis. In unparasitized, young pharate adults and third instar, wandering larvae of S. bullata, four main hemocyte types were identified by light microscopy: plasmatocytes, granular cells, oenocytoids, and pro-hemocytes. Parasitism of young pharate adults had a differential effect on host hemocytes; oenocytoids and pro-hemocytes appeared to be unaltered by parasitism, whereas adhesion and spreading behavior were completely inhibited in plasmatocytes and granular cells by 60 min after oviposition. The suppression of spreading behavior in granular cells lasted the duration of parasitism. Plasmatocytes were found to decline significantly during the first hour after parasitism and this drop was attributed to cell death. Melanization and clotting of host hemolymph did not occur in parasitized flies, or the onset of both events was retarded by several hours in comparison to unparasitized pharate adults. Hemocytes from envenomated flies were altered in nearly identical fashion to that observed for natural parasitism; the total number of circulating hemocytes declined sharply by 60 min post-envenomation, the number of plasmatocytes declined but not granular cells, and the ability of plasmatocytes and granular cells to spread when cultured in vitro was abolished within 1 h. As with parasitized hosts, the decrease in plasmatocytes was due to cell death, and inhibition of spreading lasted until the host died. Isolated crude venom also blocked adhesion and spreading of these hemocyte types in vitro. Thus, it appears that maternally derived venom disrupts host immune responses almost immediately following oviposition and the inhibition is permanent. The possibility that this ectoparasite disables host defenses to afford protection to feeding larvae and adult females is discussed.

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PubMed1997

Inhibition of testicular growth and development in Manduca sexta larvae parasitized by the braconid wasp Cotesia congregata.

Tobacco hornworm larvae parasitized by the gregarious larval endoparasitoid Cotesia congregata exhibited an inhibition in testicular growth and development, the extent of which was determined by the age and developmental stage of the host at the time of parasitization. The degree of parasitic castration, as assessed by measurements of testicular volume, was correlated with the stadium in which parasitization occurred. A mathematical formula requiring the measurement of testicular length, width and depth was used to calculate testicular volume. The use of the depth parameter revealed a negative correlation between host weight and testicular volume in parasitized larvae. Testicular volumes of fifth instar hosts, which had been parasitized in the first stadium, were significantly smaller than those originally parasitized as fourth or fifth instar larvae and were not correlated with parasitoid load. Effects of natural parasitism were not duplicated by injections of C. congregata polydnavirus and venom, topical treatment with the juvenile hormone analog methoprene, or starvation of nonparasitized larvae. Larvae receiving virus plus venom or methoprene grew larger due to delayed wandering and had larger testes than controls. Deleterious effects on host testes may be due to the effects of nutrient competition between the developing parasitoid progeny and the gonads, combined with the juvenilizing effects believed to be caused by the polydnavirus.

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PubMed1998

Male orientation to trail sex pheromones in parasitoid wasps: does the spatial distribution of virgin females matter?

We studied male locomotory response to trails and patches of sex pheromone (left respectively by free-ranging females and females constrained to stay on a small area) in the two parasitoids Aphelinus asychis (Hymenoptera: Aphelinidae) and Trichogramma brassicae (Hymenoptera: Trichogrammatidae). Under the hypothesis that the spatial distribution of virgin females differs between these species (scattered among host plants in A. asychis, gregarious at emergence sites in T. brassicae), we predicted that male locomotory response to their sex pheromones should also differ: A. asychis males should follow pheromone trails on plants in order to encounter the females along these trails, whereas T. brassicae males should stay on pheromone patches, at emergence sites, and mate the females on these patches. Using an improved video-tracking system, we found that males of both species respond to conspecific sex pheromone trails and patches, but that the response does not differ much between species. Males released on marked substrates walked in a more convoluted pattern (i.e. higher path fractal dimension and higher number of crossings within tracks) than males released on unmarked substrates. On pheromone patches, males turned persistently in the same direction when leaving the patch, which explains a higher number of visits on marked patches than on unmarked patches, and possibly, higher track convolution on pheromone trails. Contrary to our hypothesis, male A. asychis did not follow female trails more accurately than male T. brassicae, and male T. brassicae did not stay longer on pheromone patches than male A. asychis. We argue that these discrepancies between our predictions and the observed responses originates from discrepancies between the assumed spatial distribution of virgin females and their actual distribution in the wild.

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PubMed1998

Manipulation of fifth-instar host (Manduca sexta) ecdysteroid levels by the parasitoid wasp Cotesia congregata.

Although 5th (last) instar parasitized Manduca sexta larvae undergo developmental arrest and do not wander, they exhibit a small hemolymph ecdysteroid peak (300-400pg/&mgr;l) which begins one day prior to the parasitoid's molt to the 3rd (last) instar and concomitant emergence from the host. Ecdysteroids present in this peak were 20-hydroxyecdysone, 20,26-dihydroxyecdysone and one or more very polar ecdysteroids, as well as small amounts of 26-hydroxyecdysone and ecdysone. In parasitized day-1 and -2 5th instars ligated just behind the 1st abdominal proleg, hemolymph ecdysteroid levels increased in both anterior and posterior portions (100-500pg/&mgr;l), while in unparasitized larvae, hormone levels only increased in the anterior portion (100-350pg/&mgr;l). Thus, the ecdysteroid peak observed in host 5th instars was probably produced, at least in part, by the parasitoids. It may serve to promote Cotesia congregata's molt from the second to the third instar and/or to facilitate parasitoid emergence from the host. In parasitized day-1 and -2 5th instars ligated between the last thoracic and 1st abdominal segments, hemolymph ecdysteroid titers reached much higher levels (500-3500pg/&mgr;l) in the anterior portion (no parasitoids present) than in the posterior portion (150-450pg/&mgr;l). Therefore, it appears that the parasitoid's regulation of hemolymph ecdysteroid titers occurs at two levels. First, parasitization neutralizes the host's ability to maintain its normal hemolymph ecdysteroid levels. Second, in a separate action, the parasitoid manipulates the ecdysteroid-producing machinery so that hemolymph levels are maintained at the 200-400pg/&mgr;l characteristic of day 3-4 hosts. This is the first report of a parasitoid's ability to interfere with the normal inhibitory mechanisms which prevent prothoracic gland production of ecdysteroid at inappropriate periods of insect growth and development.

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PubMed1998

Genetic variability in the area searched by a parasitic wasp: analysis from automatic video tracking of the walking path.

The ability of foraging hymenopterous parasitoid females to discover their hosts, and thus to be efficient agents in biological control programs, is likely to be related to the surface they are able to prospect per unit of time. However, this behavioural trait has never been accurately estimated, and its implication in female efficiency has never been really demonstrated. This paper provides an algorithmic method that can be used to estimate this trait from an automatic recording of the females' walking path. Using stochastic procedures simulating walking tracks, this trait is shown to be strongly related to the number of hosts that parasitoid females are able to attack per unit of time. This trait was estimated for individual females of Trichogramma brassicae Bezdenko (Hymenoptera; Trichogrammatidae). On average, females of this species are able to prospect about 28mm(2)s(-1). Finally, the genetic variation in this trait was studied using the iso-female line method. A significant genetic variability was observed. It provides the basic information that is necessary to start a genetic selection of mass-reared Trichogramma in order to improve their efficiency in controlling target pests in biological control programs. The functional and evolutionary implications of these results are discussed.

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PubMed1999

Is the surface of endoparasitic wasp eggs and larvae covered by a limited coagulation reaction?

Evidence is presented for the existence of a Venturia homologue of hemomucin, a surface mucin that was recently described in Drosophila. Venturia hemomucin is part of the mucinous layer on the egg and larval surface of the parasitoid. Venturia hemomucin forms a complex with lipophorin and other host hemolymph components, that is similar to a hemomucin-lipophorin complex which is part of the coagulation reaction. The possible formation of a specific layer against the host defence system is discussed for eggs and larvae that develop inside another insect.

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PubMed2002

How signaling proteins integrate multiple inputs: a comparison of N-WASP and Cdk2.

Signal transduction proteins that can integrate multiple upstream signals play a critical role in the complex regulatory circuits that control cellular behavior. The two signaling node proteins cyclin-dependent kinase 2 and the actin regulator neuronal Wiskott-Aldrich syndrome protein have qualitatively similar signaling properties. Recent studies, however, reveal that these proteins utilize distinct mechanisms of signal integration, leading to subtle but important quantitative differences in behavior.

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