The effect of gypsy moth metamorphosis on the development of nuclear polyhedrosis virus infection

The development of nuclear polyhedrosis virus (NPV) infection in gypsy moth (Lymantria dispar) was studied before, during, and after host metamorphosis, and in larvae and pupae in the subsequent generation, to determine whether NPV ingested by late instars can replicate in host tissues through metamorphosis and whether it can be vertically transmitted to progeny. Individuals that survived sublethal dosages of NPV did not differ from undosed insects in pupal weight, fecundity, larval and pupal weight of progeny, or response of progeny to NPV challenge. No evidence of NPV infection or of abnormal histology was found in adult tissues examined by light microscopy and no virus was detected on the surface of eggs produced by NPV-treated moths. No NPV-caused mortality was recorded among undosed progeny of dosed or undosed parents. The progeny of dosed parents were neither more resistant nor more susceptible to LdMNPV than were progeny of undosed parents and lethal times did not differ between groups. Examination of larval, pupal, and adult tissues by DNA hybridization revealed that insects in which NPV DNA was detected died prior to adult eclosion. NPV was not detected in any hosts surviving to the adult stage. These results suggest that survivors of sublethal dosages of NPV avoid infection and are therefore incapable of vertically transmitting infectious virus to progeny.     

Influence of a baculovirus infection on molting and food consumption by Spodoptera litura

The effect of a baculovirus (nuclear polyhedrosis virus) infection on molting, neurosecretory activity, and food consumption of the tobacco leaf eating caterpillar. Spodoptera litura, is studied. The virus was administered by allowing the larvae to feed on castor leaves contaminated with purified polyhedral suspension (5.57 × 10⁸/ml). Host larvae failed to molt more than once after infection. Infected last-instar larvae failed to pupate and had prolonged larval stage. Activity of median neurosecretory cells (MNC) of brain increased during disease development. However, the larval—pupal molt was inhibited, possibly due to lack of release of neurosecretion from the MNC. The surface area of corpus allatum of last-instar larvae increased during infection indicating high activity. Infected larvae continued to feed almost until death. The indices of digestion and utilization were significantly lowered due to disease development.     

Transmission of a baculovirus in populations of Oryctes rhinoceros

The transmission of the baculovirus of Oryctes rhinoceros, previously called Rhabdionvirus oryctes, was studied. O. rhinoceros adults became infected with the virus when kept in a mixture of sawdust and ground-up virus-killed larvae or together with other virus-infected adults. In the field, mated females were more frequently infected than unmated females. Adults developing from larvae that had survived exposure to various dosages of the virus were not infected. No virus infections occurred in larvae hatching from eggs surface-contaminated with the virus. Larvae hatching from eggs laid by virus-infected females very rarely were infected.In the O. rhinoceros population the virus is transmitted most frequently during mating, possibly when the uninfected partner contacts virus material excreted by the infected partner. The virus can be transmitted in a similar way when infected and healthy beetles feed together in palm trees. Beetles visiting larval breeding sites containing freshly virus-killed larvae can become infected. Virus-infected beetles can pass the infection to healthy larvae when visiting a breeding site.     

Effect of dose of cytoplasmic polyhedrosis virus on infection,mortality, development rate,and larval and pupal weights of the pink bollworm

Host-pathogen relationships were studied between the pink bollworm, Pectinophora gossypiella, and a cytoplasmic polyhedrosis virus (CPV). Results showed that the median effective dose (ED₅₀), the dose that infects half the test subjects, was 1.91 × 10² polyhedral inclusion bodies (PIB)/ml of diet. The median lethal dose (LD₅₀) was 1.72 × 10⁵ PIB/ml. Diagnosis for CPV infection was more reliable in adult pink bollworms than in late-instar larvae. Duration of the larval stage increased with viral dose, but duration of the pupal stage was not affected by CPV. Weights of infected male and female pupae were 23.7 and 24.0% less than those of untreated pupae, respectively. Pupal weights were not significantly influenced by increases in the viral dose. Weights of larvae of a given age decreased as dose increased. The effect of CPV on duration of the immature stages and on pupal weight was not significantly influenced by rearing temperatures between 25.0° and 32.5°C. Pupal weight of infected pink bollworms decreased as the duration of the larval stage increased.     

Changes in growth and virulence of a nuclear polyhedrosis virus from Choristoneura fumiferana after passage in Trichoplusia ni and Galleria mellonella

An isolate of nuclear polyhedrosis virus from Choristoneura fumiferana was fed to neonate larvae of Trichopulsia ni and Galleria mellonella. It caused infection and mortality in both of these species. After passage in the alternate hosts, the isolate became increasingly virulent for these hosts. The passaged virus retained its infectivity for Choristoneura but diseased larvae did not wilt and at death they were found to contain only a few polyhedra indicating the virus had been changed.     

Food consumption by cabbage loopers infected with nuclear polyhedrosis virus

The effects of age, temperature, and dose on artificial medium consumption by healthy and nuclear polyhedrosis virus-infected cabbage looper larvae were measured using gravimetric methods. Instar in which lethal infection occurred was more closely related to subsequent food consumption than was larval age in days. Larval cabbage loopers, lethally infected in either the first or second instar, consumed 2% or less of their potential consumption. Larvae infected in the third instar consumed ca. 5% of their subsequent potential. In the fourth instar, this amount increased to ca. 10%. If infection occurred in the fifth instar, no significant amount of feeding was prevented. Increasing the virus dosage significantly decreased consumption and length of feeding period over the range of dosages tested. The relationship between consumption patterns of diseased and healthy insects remained constant over a 20–35°C temperature range.     

The transstadial and vertical transmission of a granulosis virus from the corn borer Sesamia nonagrioides

The effects of a granulosis virus from Sesamia nonagrioides were established in the larval, pupal, and adult stages. Different ages of larvae were compared as to their survival rates. Pupae deriving from diseased larvae had a sex ratio that deviated from the expected 1:1; in some of these pupae an incomplete pigmentation was noticed in abdominal segments. Adults deriving from inoculated larvae were less fertile, as measured by oviposition and by hatching rate. Offspring of inoculated parents had a greater incidence of the granulosis virus disease than did offspring of uninoculated parents.     

The consequences of egg cannibalism inAdalia bipunctata [Coleoptera: Coccinellidae]

When eggs ofAdalia bipunctata L. are offered to larvae of their own species, these larvae are able to develop to adults. Reducing the daily egg supply results in decreased larval survival and pupal weight and especially fecundity of the adult females. The duration of larval development is significantly increased, the longevity of adults is shortened.     

Effect of larval maturation on mortality induced by nuclear polyhedrosis and granulosis virus infections of Heliothis armigera

All the instars of Heliothis armigera larvae were found to be susceptible to both nuclear polyhedrosis virus (NPV) and granulosis virus (GV). An inverse relationship between mortality and larval age was found in the case of the NPV, while the GV displayed a rather erratic mortality pattern. A degree of maturation immunity against the NPV was found to exist, but the same is not true for the GV. The important role that pupation plays on the effect of a lethal infection is also discussed.     

Mode of transmission of nuclear-polyhedrosis virus to progeny of adult Heliothis zea

Late second-instar Heliothis armigera larvae were infected with a granulosis and a nuclear polyhedrosis virus, and all the externally visible symptoms for each virus are described. The effects of the virus infections on the feeding habits of the insects are also described, and it was found that a granulosis infection can prolong the larval period by up to 100%. The larvae continue feeding during this prolonged larval period, and can reach almost double the size and mass of normal larvae.It was further found that each of the viruses displays a distinct set of symptoms which could indicate beyond any doubt which of the two viruses induced death in the host.     

A laboratory study of the effects of cytoplasmic polyhedrosis virus on Heliothis virescens (Lepidoptera: Noctuidae)

Larvae of Heliothis virescens reared from eggs contaminated with cytoplasmic polyhedrosis virus weighed 50% less than those reared from virus-free eggs. The larval stage in a virus-infected group was 4 days longer than that of a healthy group, and diseased pupae weighed an average of 60 mg less than healthy pupae. Furthermore, adult emergence was reduced 10% in virus-infected pupae, diseased moths lived 9 days less than healthy moths, and production of eggs was reduced 68% in diseased females.     

Formation of virion-occluding proteinic spindles in a Baculovirus disease of Aedes triseriatus

An unusual process of inclusion formation was studied in Aedes triseriatus larvae infected with a Baculovirus (BV) similar to the nuclear polyhedrosis virus (NPV) type. In this disease virion-occluding proteinic inclusions initially developed individually. However, as the disease progressed the proteinic inclusions gradually coalesced eventually forming large rugose ellipsoids and finally, large smooth-surfaced spindles. Nuclei in late stages of infection usually contained two to five rugose ellipsoidal inclusions, frequently measuring 5 μm to 7 μm in diameter by 10 μm to 15 μm in length. The ellipsoidal forms exhibited different chemical behavior from the spindles.     

Effects of cytoplasmic polyhedrosis virus on diapausing Heliothis virescens

Laboratory studies were conducted to determine effects of cytoplasmic polyhedrosis virus on diapausing Heliothis virescens. Most virus-infected individuals died in the larval stage. Infected pupae yielded as many moths as healthy. Females from surviving virus-infected larvae produced fewer eggs than those from healthy larvae, but there was no statistical difference in longevity of adults between healthy and infected groups. Infected moths yielded lower than normal quantities of extracted fatty acids.     

Infection of the Cat Flea, Ctenocephalides felis (Bouché) by Neoaplectana carpocapsae Weiser

Infection of cat flea, Ctenocephalides felis, larvae by the entomophilic nematode Neoaplectana carpocapsae was accomplished in the laboratory. The Breton strain of N. carpocapsae provided higher larval mortality at lower dosages than did the DD-136 strain. Adult nematodes were evident in the insect hemocoel after 48 h; however, no infective third-stage larvae were produced. Larval flea infection increased with an increase in the moisture content of sand from 2% to 7% and of sandy clay from 7% to 12%. Larval flea infection was also obtained on turf containing dauer larvae. Nematode penetration of cocoons with invasion of prepupal and pupal fleas was apparent.     

Nuclear polyhedrosis virus infection ofPseudoplusia includens [Lep.: Noctuidae] larvae: Effect on post larval stages and transmission

Treatment ofPseudoplusia includens (Walker) larvae in either the 4th, 5th or 6th stage with a nuclear polyhedrosis virus (NPV) did not affect the weight or sex ratio of surviving pupae. Pupal mortality was low but increased with the dosage of the NPV larvae had received. Also, mortality of pupae from larvae treated in the 5th or 6th stage was higher than from larvae treated in the 4th stage. Adult longevity was not affected by the virus. Fecundity and egg viability were reduced following most treatments of 6th stage larvae but not 4th or 5th stage larvae. Adults exposed to NPV at 3 dosages during the 6th larval stage were released in cages on soybean. Some of the progeny succumbed to NPV infection. Progeny mortality increased over a 7 week period of adult release, but did not differ significantly between treated and untreated groups by the end of the 7 week period.     

Infection of a nucleopolyhedrovirus to Neodiprion zhejiangenis Zhou & Xiao (Hymenoptera: Diprionidae)

Neodiprion zhejiangenis Zhou &; Xiao 1981 (Hymenoptera: Diprionidae) nuclear polyhedrosis virus (NezhNPV) is a biocontrol factor with high development potential and application prospects. To study the insecticidal activity of NezhNPV against the larvae of N. zhejiangenis, the susceptibility of larvae at different instars to different NezhNPV concentrations was determined based on laboratory bioactivity. At 2.0?×?10⁷ polyhedron inclusion body (PIB)/mL, the median lethal time required to kill 50% of the instar 2 and 3 larvae was approximately 5 d, whereas the median lethal time of the instar 4 and 5 larvae was 8–9 d. Interestingly, at the NezhNPV concentrations of 2.0?×?10³ and 2.0?×?10⁴ PIB/mL, the feeding ability of the surviving larvae was decreased by 57.4% and 76.4%, respectively, compared with the controls; the pupal weight at both concentrations was decreased by approximately 27%, and the adult emergence rate was decreased by 27.4% and 50.9%, respectively, with a significantly higher proportion of males than of females. The results showed that younger instar larvae of N. zhejiangenis were more susceptible to NezhNPV infection than older instar larvae. The larval mortality rate was dependent on the larval instar and NezhNPV concentration.     

Dynamics of Baculovirus Growth and Dispersal in Mamestra brassicae L. (LepidopteraNoctuidae) Larval Populations Introduced into Small Cabbage Plots

The nuclear polyhedrosis virus of Mamestra brassicae has been studied in larval populations of the moth introduced into small plots of cabbages. Primary dispersal of virus from single foci of infected larvae resulted from enhanced movement of the larvae, which colonized new plants logarithmically. Virus growth within the host population was quantified, and infection of young larvae in the following generation was related directly to the concentration of virus produced during the primary phase. Secondary cycling of virus resulted in dispersal of inoculum from multiple foci, and a large proportion of plants were ultimately colonized by infected larvae. The dynamics of virus growth during secondary dispersal were quantified and contrasted with results from the primary phase. The significance of these results is discussed in relation to possible control of insect pests through dispersal of virus by the host insect.     

Lack of absorption and rapid elimination of Rifampicin as factors precluding tests against nuclear polyhedrosis in Spodoptera littoralis larvae

Rifampicin administered per os in artificial medium to first-instar larvae of Spodoptera littoralis together with nuclear polyhedrosis virus did not affect virus infection and resulted in total larval mortality. A pharmacokinetic study of this antibiotic was carried out by means of a microbiological assay. Using Bacillus thuringiensis var. thuringiensis as the test organism for assaying the antibiotic, as little as 0.5 μg of Rifampicin could be detected in the presence of hemolymph, and no such detectable amounts could be found in the hemolymph of sixth instar larvae which had been fed the antibiotic. Most if not all of the antibiotic was in the feces, excreted in active form. When given parenterally, Rifampicin was detected in the hemolymph 30 min after injection but not 24 hr thereafter, when active antibiotic was found concentrated in the first fecal pellets evacuated after injection. This disappearance is ascribed to excretion via the Malpighian tubules. The larval responses detailed above preclude the testing of Rifampicin as an antiviral drug against nuclear polyhedrosis.     

Sublethal effects of Bacillus thuringiensis on the spruce budworm, Choristoneura fumiferana

Exposing larvae of the spruce budworm, Choristoneura fumiferana (Clemens), to sublethal ( 50% lethal dose) levels of Bacillus thuringiensis subsp. kurstaki at various stages of their development significantly increased development time to the pupal stage and reduced pupal size and number of eggs laid per female, but did not affect the proportion of embryonated eggs. The changes in larval development time, pupal weight and fecundity depended on the larval stage that was treated. Exposure of fourth instars delayed larval development and reduced only male pupal weights with no effects on fecundity. Exposure of sixth instars delayed larval development to a lesser extent than exposure of fourth instars but had a pronounced effect on weight of both male and female pupae. The effect on pupal weight was sex dependent, as males tended to be more affected than females. The reduction in male pupal weight did not appear to influence fecundity, because the effect of exposure was explained by the change in female pupal weight. Effects on larval growth and pupal weight were proportional to the dose that was ingested during exposure, and were observed at doses as low as one-tenth of the LD₅₀. Ingestion of an LD₅₀ caused a 29 or 45% delay in development of, respectively, female or male larvae when exposed as fourth instars and a 30% reduction in female pupal weight when larvae were exposed as sixth instars.