NPV-infected Larvae Research Articles

Host plants affect the susceptibility of Spodoptera exigua to its homologous nucleopolyhedrovirus: role of chitin synthase and intestinal mucin in the peritrophic matrix

ABSTRACT Host plants have an effect on the susceptibility of lepidopteran insects to nucleopolyhedrovirus (NPV), but the role of the protein in peritrophic membrane (PM) of larvae has not been investigated. We determined a key PM gene (SeIIM8 gene) in Spodoptera exigua (Hübner), which plays a role in protecting against NPV infection. Then we quantified the activity of chitin synthase (SeCHS), the content of insect intestinal mucin (SeIIM) and the expression of their genes in S. exigua fed one of four foods (artificial diet, Brassica oleracea (L.), Glycine max (L.), or Ipomoea aquatica (Forsskal)) with or without inoculation of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV). Our results showed that the larval mortality was highest for NPV-infected with siRNA-injected larvae, intermediate for NPV-infected larvae, and lowest for uninfected larvae. The SeCHS activity, SeIIM content, and their relative gene expressions of S. exigua fed G. max or artificial diet were lower compared to caterpillars fed other diets. The relative SeCHS and SeIIM8 gene expression levels of larvae depended on the interaction of NPV treatment, diet, and time. This study concluded that plants affected the susceptibility of insects to NPV by altering the enzyme activity and gene expression of insects.

Nucleopolyhedrovirus infection enhances plant defences by increasing plant volatile diversity

ABSTRACTPlant–herbivore–entomopathogen tri-trophic interactions and biodiversity are relatively understudied topics in ecology. Particularly, the effects of entomopathogens on herbivore-induced plant volatiles and plant volatile diversity on the defensive function of plants have not been studied in detail. We used soybean (Glycine max), beet armyworm larvae (Spodoptera exigua), and nucleopolyhedrovirus (NPV) as a tri-trophic system to determine whether NPV infection can promote the emission and diversity of volatiles from plants. We also investigated whether NPV infection affects the attraction of Microplitis pallidipes, an important endoparasitoid of larval S. exigua. Uninfested soybean plants released 7 detectable volatile compounds while plants fed upon by healthy and NPV-infected S. exigua larvae released 12 and 15 volatiles, respectively. Female parasitoids were more attracted to the volatiles from plants that were fed upon by NPV-infected larvae than healthy larvae, and more attracted to the volatiles from plants that were fed upon by healthy larvae than no larvae. The selective responses of parasitoids to plant odours increased as plant volatile diversity increased. Our study suggests that the NPV infection facilitates the release of plant volatiles and enhances the defensive function of plants by increasing plant volatile diversity which in turn attracts more parasitoids. Also, this work reveals that plants might accrue two indirect benefits from NPV infection, cessation of herbivore feeding and more parasitisation.

Formulation and optimisation of various nuclear polyhedrosis virus isolates and assessment of their insecticidal activity against Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) larvae

Helicoverpa armigera (Hubner) is a pest that poses serious threat to the tomato crop in India. Larvae of this species are susceptible to the nucleopolyhedrovirus (NPV), which has attracted interest as a potential biocontrol agent. Rearing of larvae in natural diet resulted in less number of pupae, while in artificial diet more pupae and healthy adults were obtained. The NPV was tested for its insecticidal action against H. armigera in natural and artificial diets. The bioassay results of inoculated H. armigera nucleopolyhedrosis virus (HaNPV) with different concentrations indicate that the 4.0 g/l dosage caused maximum mortality (70.3% and 60.54%), and minimum mortality 46.83% and 44.08% was recorded in the 0.5 g/l dosage under laboratory and pot culture conditions, respectively. Polyhedral inclusion bodies (PIBs) were estimated using a standard haemocytometer. According to the estimate, purified PIBs were found at a concentration of 1 × 109/ml. The different formulation of NPV, i.e. wettable fine powder with a hue of white, had a particle size of 100 μm with a concentration of 1 × 108/ml. The encapsulated product was found to be in the form of beads and was red in colour with a concentration of 1 × 108 PIBs/ml. The effectiveness of NPV against H. armigera larvae was noted at maximum LC50 values at a concentration of 1 × 109/ml. Qualitative analysis estimates showed that protein polyhedrin and enzyme chitinase had a molecular weight of 33 and 45 kDa, respectively. Viral DNA was isolated from NPV-infected larvae and was then separated using SDS-PAGE. The estimated polyhedrin with a molecular weight of 33 kDa, which is responsible for the increased mortality percent of larvae, was confirmed by the bioassay. Hence it was concluded that NPV is ecofriendly in the management of pests on tomato and other crops.

Cloning and comparative characterization of three distinct nucleopolyhedroviruses isolated from the common cutworm, Spodoptera litura (Lepidoptera: Noctuidae) in Japan

A total of 189 nucleopolyhedrovirus (NPV) clones were obtained from the NPV-infected larvae of the common cutworm, Spodoptera litura, collected in Japan. Restriction endonuclease (REN) analysis demonstrated that these 189 S. litura NPV (SpltNPV) clones exhibited 33 distinct REN patterns that represented three distinct NPV types designated as type A, type B, and type C SpltNPVs based on the similarity of overall REN patterns. Comparative examination of REN patterns from these clones in this study with those from NPVs published previously indicated that type A SpltNPV corresponded to Spodoptera littoralis NPV (SlNPV)-D or SlNPV-B, whereas type B SpltNPV corresponded to the NPVs widely identified in S. litura larvae in Japan, China, and the Philippines. The overall REN pattern of type C SpltNPV did not resemble REN patterns from any of those NPVs previously identified in S. litura and S. littoralis and was distinct from the REN patterns of NPVs from Autographa californica, Bombyx mori, Hyphantria cunea, Spodoptera exigua, Lymantria dispar, and Orgyia pseudotsugata, suggesting that type C SpltNPV was a novel NPV pathogenic for S. litura. Comparative characterization with S. litura cultured cells and larvae showed that the biological properties with respect to productivity and virulence differed significantly not only among the types of SpltNPV but also among the variants within a SpltNPV type, demonstrating that SpltNPV-C3, a clone from type C SpltNPV, caused rapid mortality of S. litura larvae compared with those clones of type A or type B SpltNPV. These results indicate that the natural heterogeneity of baculoviruses can be exploited to develop NPV strains suitable for the control of S. litura and suggest that the novel SpltNPV-C3 isolated in this study has high potential to be developed as an effective pest control agent for S. litura.

Transmission of Nuclear Polyhedrosis Virus Prior to Death of Infected Loblolly Pine Sawfly, Neodiprion taedae linearis Ross, on Loblolly Pine

Nuclear polyhedrosis virus (NPV) was transmitted by infected loblolly pine sawfly, Neodiprion taedae linearis Ross, larvae prior to death on loblolly, pine. Third instars reared on pine foliage previously fed upon for 24 h by NPV-infected larvae at densities of 4 and 16 per terminal resulted in up to 69.9 and 93.1% mortality, respectively, in previously unexposed cohorts. Third instars reared on pine foliage wetted with washings from frass of infected larvae also resulted in a high level of mortality. Results suggest that a high level of secondary transmission of NPV occurs before death of primary-infected larvae. This transmission appears to be the result of NPV in the digestive tract released either through regurgitation or in the feces.

Cannibalism on nuclear polyhedrosis virus infected larvae by Heliothis armigera (Hubn.) and its effect on viral infection

Studies on cannibalism by Heliothis armigera (Hubn.) larvae on nuclear polyhedrosis virus (NPV)-infected larvae and feeding on virosed cadavers indicated that feeding was significantly higher on 4-day-old virosed cadavers followed by 1-day-old cadavers than on healthy or NPV-infected living larvae. The data revealed that cannibalism was significantly higher on NPV-infected (3 days post inoculation) larvae than either healthy larvae or those which had been just inoculated. However, the extent of feeding was higher on healthy larvae (cannibalistic feeding) than on cadavers. Significantly more number of larvae became infected by NPV when they fed on NPV-killed cadavers than on NPV-infected living larvae. Some of the larvae which had fed on either virosed cadavers or NPV-infected larvae survived. But, the disease was expressed in the pupal stage. Pupal mortality was significantly higher in larvae which fed on NPV-inoculated larvae (3 days post inoculation). The multiple choice test to find out the feeding preference of the larvae showed that the larvae had a greater preference to feed on virosed cadavers than either the healthy larvae or the host plant. The role of cannibalistic behaviour in the dissemination of the virus disease under field conditions is discussed.

Transmission of Nuclear Polyhedrosis Virus by the Parasitoid Microplitis croceipes (Hymenoptera: Braconidae) to Heliothis virescens (Lepidoptera: Noctuidae) on Soybean

Transmission of Heliothis nuclear polyhedrosis virus (NPV) by the parasitoid Microplitis croceipes (Cresson) to Heliothis virescens (F.) larvae was examined. Mortality from NPV occurred in larvae exposed to Heliothis NPV-contaminated female parasitoids in the laboratory and on soybean in the field. In single-plant and large-cage field tests, mortality from Heliothis NPV in larvae exposed to virus-contaminated parasitoids was higher when the parasitoid's entire body surface had been artificially contaminated with virus than when only the parasitoid's ovipositor and surrounding area were artificially contaminated or when the parasitoid was previously allowed to oviposit in Heliothis NPV-infected larvae. The level of mortality from Heliothis NPV in caged larvae also increased as the parasitoid density in the cage increased from 0.25 to 3.0 per meter of row.

Discrete and Interactive Effects of Plant Resistance and Nuclear Polyhedrosis Viruses for Suppression of Soybean Looper and Velvetbean Caterpillar (Lepidoptera: Noctuidae) on Soybean

Laboratory and fieid tests with two nuclear polyhedrosis viruses (NPV) infective to the soybean looper (SBL), Pseudoplusia includens (Walker), and velvetbean caterpillar (VBC), Anticarsia gemmatalis Hübner, were conducted to investigate the effects of their integration with resistant host plants for suppression of SBL and VBC on soybean, Glycine max (L.) Merrill. The soybean genotypes were an insect resistant soybean breeding line GatIR 81-296 and a susceptible cultivar (‘GaSoy 17’). In the laboratory study, foliage consumption of late-ins tar SBL reared on the resistant genotype was severely inhibited, but VBC foliage consumption was not different on the two genotypes. NPV-infected larvae of both species consumed significantly less foliage when reared on the resistant genotype than on the susceptible genotype. Although total numbers of SBL and VBC larvae generally were not significantly lower in field plots of the resistant genotype, numbers of medium-sized VBC and large SBL larvae were significantly reduced on the resistant genotype during times of peak population density. An application of VBC NPV reduced total numbers of VBC larvae by 76% (‘GaSoy 17’ plots) and 72% (81-296 plots) at 7 d after application. SBL NPV appeared to work more slowly against host larvae; however, total numbers of SBL larvae were suppressed by 78% (‘GaSoy 17’ plots) and 76% (81-296 plots) by 14 d after application. Both pathogens were effective in reducing numbers of host larvae and percentage of defoliation in plots of resistant or susceptible soybean.

Nabis roseipennis Adults (Hemiptera: Nahidae) as Disseminators of Nuclear Polyhedrosis Virus to Anticarsia gemmatalis (Lepidoptera: Noctuidae) Larvae1

Nabis roseipennis Reuter adults that had fed on nuclear polyhedrosis virus (NPV) infected Anticarsia gemmatalis Hubner larvae in late stages of infection excreted infective virus for several days. The mean amount of virus in the excreta for the 10-d test period was 5.3 ± 0.9 × 106 polyhedral inclusion bodies, with 98% excreted during the first 2 d after feeding on infected larvae. When uninfected larvae were caged for 4 d on soybean plants with N. roseipennis adults (densities of one, two, or four adults/plant) that had fed on NPV-infected larvae, larval mortality from NPV varied from 6.7 ± 2.2 to 16.8 ± 3.9% in the low- and high-density treatments, respectively.

Efficacy of Combinations of Polyhedrosis Viruses and Permethrin Against the White Cutworm, Euxoa scandens (Riley) (Lepidoptera: Noctuidae)

Laboratory tests were conducted to evaluate the effect of simultaneous and sequential treatments of cytoplasmic or nuclear polyhedrosis viruses and a synthetic pyrethroid, permethrin (Ambush),on the larvae of Euxoa scandens (Riley). A significant increase in total mortality occurred when permethrin was applied to larvae previously infected for a period of 4 to 7 days with virus. Comparisons of infected and noninfected larvae indicated that the toxicity of permethrin increased by 1.51-fold for CPV-infected larvae after 6 days of infection and 4.18-fold for NPV infected larvae.

A Tipula paludosa population with a high incidence of two pathogens

The incidence of lethal parasites in the larvae of a Tipula paludosa population was monitored for two seasons. The proportions of larvae infected with Tipula iridescent virus (TIV) and a tachinid insect were similar to those in previously studied populations, whereas the proportions of larvae infected with Tipula nuclear polyhedrosis virus (NPV) and a spore-forming bacterium (SFB) were higher. Conservative estimates of mortality due to these four agents were 10.7% in 1977–1978 and 7.7% in 1978–1979. The mean population density and the proportion of SFB-infected larvae were lower in 1978–1979 than in 1977–1978, while the proportion of NPV-infected larvae was higher. In 1979 the proportion of NPV-infected larvae was positively correlated with population density, which was highest in the wettest part of the study area. In both seasons the proportion of SFB-infected larvae was negatively correlated with population density. Larvae infected with the NPV or the SFB became pallid at an advanced stage of infection, but, although infected larvae were found throughout the larval period, pallid larvae were only found in the later part. It is suggested that larvae become infected in an early instar, then the infections slowly develop throughout the remainder of the larval period. Five larvae were found with mixed infections; four were infected with the SFB and NPV, while the fifth was infected with the SFB and TIV.

Interaction of Campoletis sonorensis and a nuclear polyhedrosis virus in larvae of Heliothis virescens.

Development of the parasite, Campoletis sonorensis (Cameron), in larvae of Heliothis virescens (F.) infected with a nuclear polyhedrosis virus (NPV) rarely proceeded beyond the 1st instar if host larvae were exposed to the NPV prior to parasitization. Significant numbers of parasites survived only in NPV-infected larvae if exposure to the virus was delayed by 48 h following parasitization. Although polyhedral formation could not be detected within cells of the parasite, numerous polyhedra were found in the midgut lumens of parasitic larvae examined histologically. Such ingested polyhedra were voided in the parasite’s meconium during pupation, and adults were free of detectable polyhedra and symptoms of virus infection. However, female parasites which had developed in NPV-infected hosts were capable of transmitting the virus to healthy Heliothis larvae. Direct evidence that transmission was effected by the parasite’s ovipostor was obtained when healthy parasites were allowed to oviposit in an infected larva and then immediately permitted to oviposit in healthy larvae. While increased spread of the virus might be achieved, the practicality of coordinating inundative releases of the parasite with use of the NPV as a microbial insecticide would appear to be negated by the fact that the host-parasite-pathogen interactions are rather highly detrimenta1 to the parasite.