Parasitization of Manduca sexta larvae by the parasitoid wasp Cotesia congregata induces an impaired host immune response

During oviposition, the parasitoid wasp Cotesia congregata injects polydnavirus, venom, and parasitoid eggs into larvae of its lepidopteran host.. the tobacco hornworm, Manduca sexta. Polydnaviruses (PDVs) suppress the immune system of the host and allow the juvenile parasitoids to develop without being encapsulated by host hemocytes mobilized by the immune system. Previous work identified a gene in the Cotesia rubecula PDV (CrV1) that is responsible for depolymerization of actin in hemocytes of the host Pieris rapae during a narrow temporal window from 4 to 8 h post-parasitization. Its expression appears temporally correlated with hemocyte dysfunction. After this time, the hemocytes recover, and encapsulation is then inhibited by other mechanism(s). In contrast, in parasitized tobacco hornworm larvae this type of inactivation in hemocytes of parasitized M. sexta larvae leads to irreversible cellular disruption. We have characterized the temporal pattern of expression of the CrV1-homolog from the C. congregata PDV in host fat body and hemocytes using Northern blots, and localized the protein in host hemocytes with polyclonal antibodies to CrV1 protein produced in P. rapae in response to expression of the CrV1 protein. Host hemocytes stained with FITC-labeled phalloidin, which binds to filamentous actin, were used to observe hemocyte disruption in parasitized and virus-injected hosts and a comparison was made to hemocytes of nonparasitized control larvae. At 24 h post-parasitization host hemocytes were significantly altered compared to those of nonparasitized larvae. Hemocytes front newly parasitized hosts displayed blebbing, inhibition of spreading and adhesion, and overall cell disruption. A CrV1-homolog gene product was localized in host hemocytes using polyclonal CrV1 antibodies, suggesting that CrV1-like gene products of C. congregata's bracovirus are responsible for the impaired immune response of the host. (C) 2005 Elsevier Ltd. All rights reserved.

Effects of temperature, salinity, desiccation and chemical treatments on egg embryonation and hatching success of Benedenia seriolae (Monogenea : Capsalidae), a parasite of farmed Seriola spp.

The effects of temperature and salinity on the embryonation period and hatching success of eggs of Benedenia seriolae were investigated. Temperature strongly influenced embryonation period; eggs first hatched 5 days after laying at 28 degreesC and 16 days after laying at 14 degreesC. The relationship between temperature and embryonation period is described by quadratic regression equations for time to first and last hatching. Hatching success was >70% for B. seriolae eggs incubated at temperatures from 14 to 28 degreesC. However, no B. seriolae eggs embryonated and hatched at 30 degreesC and

Bioactivity of Fusarium oxysporum f. sp glycines and Sclerotium rolfsii filtrates on egg hatching, survival and infectivity of juveniles of Meloidogyne incognita race 2

The effects of culture filtrates of Fusarium oxysporum and Sclerotium rolfsii on egg hatching and juvenile survival of Meloidogyne incognita in vitro and impact of these filtrates on infectivity of M. incognita were investigated on soybean seedlings. Five- and 10-day-old filtrates of F. oxysporum caused 65 and 54% egg-hatching inhibition, while that of S. rolfsii caused 61 and 49% inhibition, respectively. Juveniles of M. incognita died within 6 days when incubated in 5-day-old filtrate of F. oxysporum, while the similar filtrate of S. rolfsii caused 100% juvenile mortality on the fifth day. Filtrates reduced root galling, egg population, number of adult females in soybean plants at harvest and also soil population. Culture filtrates could be used as source of biological nematicides.

Field evaluation of anthelmintic drug sensitivity using in vitro egg hatch and larval motility assays with Necator americanus recovered from human clinical isolates

A field-applicable assay for testing anthelmintic sensitivity is required to monitor for anthelmintic resistance. We undertook a study to evaluate the ability of three in vitro assay systems to define drug sensitivity of clinical isolates of the human hookworm parasite Necator americanus recovered from children resident in a village in Madang Province, Papua New Guinea. The assays entailed observation of drug effects on egg hatch (EHA), larval development (LDA), and motility of infective stage larvae (LMA). The egg hatch assay proved the best method for assessing the response to benzimidazole anthelmintics, while the larval motility assay was suitable for assessing the response to ivermectin. The performance of the larval development assay was unsatisfactory on account of interference caused by contaminating bacteria. A simple protocol was developed whereby stool samples were subdivided and used for immediate egg recovery, as well as for faecal culture, in order to provide eggs and infective larvae, respectively, for use in the egg hatch assay and larval motility assay systems. While the assays proved effective in quantifying drug sensitivity in larvae of the drug-susceptible hookworms examined in this study, their ability to indicate drug resistance in larval or adult hookworms remains to be determined. (c) 2005 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

Evolutionary origin of Venturia canescens virus-like particles

Insect host-parasitoid interactions provide fascinating examples of evolutionary adaptations in which the parasitoid employs a variety of measures and countermeasures to overcome the immune responses of its host. Maternal factors introduced by the female wasps during egg deposition play an important role in interfering with cellular and humoral components of the host's immune defence. Some of these components actively suppress host immune components and some are believed to confer protection for the developing endoparasitoid by rather passive means. The Venturio conescens/Ephestia kuehniella parrositoid-host system is unique among other systems in that the cellular defence capacity of the host remains virtually intact after parasitization. This system raises some important questions that are discussed in this mini-review: If immune protection of the egg and the emerging larva is achieved by surface properties comprising glycoproteins and virus-like particles (VLPs) produced by the female wasp, why is the prophenoloxidose activating cascade blocked in parasitized caterpillars? Another question is the evolutionary origin of these particles, given that the functional role and structural features of V. canescens VLP proteins are more related to cellular proteins than to viruses.

Evaluation of different models to describe egg and pupal development of Xyleborus fornicatus Eichh. (Coleoptera: Scolytidae), the shot-hole borer of tea in Sri Lanka

Abstract Development data of eggs and pupae of Xyleborus fornicatus Eichh. (Coleoptera: Scolytidae), the shot-hole borer of tea in Sri Lanka, at constant temperatures were used to evaluate a linear and seven nonlinear models for insect development. Model evaluation was based on fit to data (residual sum of squares and coefficient of determination or coefficient of nonlinear regression), number of measurable parameters, the biological value of the fitted coefficients and accuracy in the estimation of thresholds. Of the nonlinear models, the Lactin model fitted experimental data well and along with the linear model, can be used to describe the temperature-dependent development of this species.