Epizootiology of a nuclear polyhedrosis virus in European spruce sawfly (Gilpinia hercyniae): the rate of passage of infective virus through the gut of birds during cage tests.

The passage of a nuclear polyhedrosis virus (NPV) of the sawfly, Gilpinia hercyniae, through avian gut was studied during cage tests on Sturnus vulgaris (three individuals), Parus ater (one), Parus caerulus (five), and Parus major (one). Following brief infection feeds, polyhedral inclusion bodies of the virus could be detected in bird feces within 0.5 hr. Peak passage of polyhedra occurred in less than 1 hr and none were detected after 2.5 hr. The feces of all birds remained infective (in bioassay tests using first instar G. hercyniae larvae) to the end of the day of infection while those of nine birds remained infective to the next day and of six birds to the third day. One bird, P. major, was also infective on Days 4, 6, and 7. The infectivity of NPV in feces stored for 2 years at +3°C declined by half. Though the scale of their epizootiological contribution is unknown, the comparatively long retention and passage of infective virus suggests birds may be effective in short- and long-distance transport of baculoviruses.     

Biomodal patterns of mortality from nuclear polyhedrosis virus in gypsy moth (Lymantria dispar) populations

A bimodal temporal pattern of mortality caused by the nuclear polyhedrosis virus (NPV) was observed in nine gypsy moth (Lymantria dispar) populations of varying densities. In all cases, peak mortality from NPV occurred during the second wave (late larval instars) and the highest mortality occurred in high density populations. Patterns of NPV mortality were established several weeks before being expressed. There was no discernible correlation between weekly mortality rates and temperature, rainfall, or total solar radiation. The bimodality was also apparent in NPV contamination on foliage which was measured by bioassay. A similar pattern was observed in the laboratory among larvae reared in groups from field-collected egg masses and from eggs artificially contaminated with NPV from a laboratory population. As in field populations, the period of low mortality from NPV between the two waves occurred when most larvae were late third and fourth instars. Larvae reared individually did not exhibit the second wave of mortality.     

The importance of birds in the dispersal of nuclear polyhedrosis virus of European spruce sawfly, Gilpinia hercyniae (Hymenoptera: Diprionidae) in Mid-Wales

The discovery of nuclear polyhedrosis virus disease (NPV) of Gilpinia hercyniae (Hartig) in bird droppings had given rise to the suggestion that birds might be important in virus dispersal. Advantage was taken of the continuing spread of sawfly and virus to sample larvae in an area with sawfly and virus, and in adjacent areas with sawfly only: bird dropping were also collected in the latter. In the previously virus-free areas, NPV was identified in some larvae but not in bird droppings. It is therefore suggested that sawfly adults might be major agents of dispersal.

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Résumé La découverte du virus de la polyédrose nucléaire (NPV) dans les excréments d'oiseaux a conduit à penser que ces derniers pourraient jouer un rôle important dans la dispersion de ce virus. On a profité du fait de l'extension continue de la tenthrède et de son virus, pour sélectionner et échantillonner d'une part des larves de tenthrèdes, d'autre part des excréments d'oiseaux, dans des zones contaminées ou non par le virus. Dans les zones non encore atteintes par l'épidémie de la virose, le virus NPV fut cependant identifié dans quelques larves mais non dans les excréments d'oiseaux. Il est donc suggéré que les tenthrèdes adultes pourraient être les agents principaux de la dispersion du virus.

     

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.     

Tipula iridescent virus infection in the developmental stages of Tipula oleracea

Tipula iridescent virus (TIV) is infective to all four larval instars, pupae, and adults of both sexes of Tipula oleracea, and iridescence has been observed in infected insects at all these stages. Third- and fourth-instar larvae were more resistant to ingested TIV than first and second instars. When TIV was injected into the hemocoel, the results suggested a possible decrease in resistance from the third larval instar to the pupa. Incubation periods (times from injection of TIV to appearance of iridescence) were significantly shorter in older fourth-instar larvae than in younger fourth-instar or thirdinstar larvae, but variability in incubation period was significantly greater in younger fourth-instar larvae than in the other two stages. Many insects which were inoculated with TIV in one stage developed iridescence and died in later stages. The amounts of infective TIV in two infected adults were estimated.     

An RNA virus in Autographa californica nuclear polyhedrosis virus preparations: Incidence and influence on baculovirus activity

A small RNA virus infectious to Trichoplusia ni larvae (TRV) was observed as a contaminant of several Autographa californica nuclear polyhedrosis virus preparations (AcMNPV). The extent of contamination in various AcMNPV preparations was studied by means of serial enrichment passages through T. ni larvae and enzyme-linked immunosorbent assay (ELISA). TRV could not be detected by ELISA in the original preparation of AcMNPV polyhedra prepared in 1968 even after five enrichment passages. Antibody inactivation offers a possible prophylactic method against TRV but temperature inactivation (55°C) does not. Although TRV reduced larval weight, it had little or no effect on bioassays of AcMNPV to T. ni and Heliothis virescens.     

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.     

Susceptibility of Heliothis armiger to a commercial nuclear polyhedrosis virus

The susceptibility of Heliothis armiger larvae of different ages to a commercial nuclear polyhedrosis virus (NPV), Elcar, was determined by bioassay. The median lethal dosage (LD₅₀) increased 150-fold during the first week of larval life at 25°C, i.e., during development to early fourth instar, but daily feeding rate and thus potential virus acquisition also increased. A linear relationship was determined between log LD₅₀ and larval length, indicating that larval length constitutes a useful index for estimating the susceptibility of larval populations. Median lethal times (LT₅₀s) were similar for larvae tested at ages of 0 to 7 days and ranged from 3.6 to 8.0 days at 30°C. The amount of virus produced in a single, infected neonate was equivalent to 1.4 × 10⁶ LD₅₀s for neonates, a 900,000-fold increase on the dose supplied. The data support the practice of directing the NPV against neonates, but, on the basis of larval susceptibility alone, the age of larvae at treatment may not always be critical.     

Interactions between Vairimorpha necatrix,Vairimorpha sp., and a nuclear polyhedrosis virus from Rachiplusia ou in Agrotis ipsilon larvae

Vairimorpha sp. and V. necatrix were assayed in combination with one another, and independently, with a nuclear polyhedrosis virus (RoMNPV) from a mint looper, Rachiplusia ou, against neonate and third-stage black cutworm larvae, Agrotis ipsilon. Initially the effect of Vairimorpha sp. was subadditive, additive, or slightly inhibiting to the V. necatrix in the dual microsporidian assays; later, V. necatrix antagonized the effect of the Vairimorpha sp. In combination with Vairimorpha sp. gradients, V. necatrix significantly (P < 0.05) reduced, in most instances, the LT₅₀ values in both neonate and third-stage larval assays. RoMNPV assayed against neonate and third instars, in combination with either Vairimorpha sp. or V. necatrix gradients, usually significantly reduced the LT₅₀ values (P < 0.05). RoMNPV, when combined with either Vairimorpha species, had varying effects on its pathology. In all assays, the particular relationship that was expressed seemed to be a function of the concentration of each pathogen, which may indicate that the two microorganisms compete for entry and/or infective sites within the larval host. Larval size, which was significantly reduced (P < 0.05) by both microsporidia, would be involved in such competition because it would limit the tissue mass available for infection. Histological examinations of larvae with dual infections revealed pathogens in the tissues that they normally infect. Vairimorpha sp. primarily infected epithelial, fat body, and Malpighian tubule tissue and, occasionally, muscle tissue. Viral polyhedral inclusion bodies were found in the same fat body tissues as the Vairimorpha spores.     

Impact of prey infected by nuclear polyhedrosis virus on a predator, Sycanus leucomesus Walk. (Hem., Reduviidae)

Abstract: An assassin bug, Sycanus leucomesus Walk. (Hem., Reduviidae) fed on nuclear polyhedrosis virus (NPV)-infected larvae of Spodoptera litura Fabr. (Lep., Noctuidae) inflicted variable effect on its developmental biology. The impact varied with the duration the predators were exposed. The predators that were fed infected prey throughout their lives appeared normal but they had significantly smaller sizes of head capsules and shorter tibial lengths than those fed healthy prey. These individuals had their overall pre-imaginal survival rate reduced by 10% from 91.25 to 81.25%, pre-oviposition period prolonged to more than 12 days, longevity reduced by 10 and 19 days in the males and females, respectively, and fecundity reduced to 41%. Even though ingestion of NPV could adversely influence their biology, the predators could serve as disseminators of the pathogen. The predators defecated infective viral polyhedral inclusion bodies (PIBs) ranging from 1.22 to 1.60 × 10¹⁰/deposit with an average of 1.42 × 10¹⁰. This NPV, when fed to its original host, caused 97% larval mortality within 10 days. Thus in nature, S. leucomesus may suppress the pest population not only by predation but also by dispersing the pathogen.     

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.     

Infectivity of nuclear polyhedrosis virus extracted with digestive juices

Autographa californica NPV, which had been obtained by dissolving polyhedra in the digestive juice of Estigmene acrea larvae, was infectious to a Trichoplusia ni cell line (TN-368). Virions thus botained were infective, and as few as 0.0025–0.005 polyhedral equivalents could infect newly transferred tissue culture cells. Activity decreased after 8 min of digestion.     

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.     

Temperature reconstruction in the Ob River valley based on ring widths of three coniferous tree species

Tree core samples of larch (Larix sibirica Ledeb.), spruce (Picea obovata Ledeb.) and pine (Pinus sibirica Du-Tour.) from the northern taiga of West Siberia were collected to assess their potential for summer temperature reconstructions in the Ob River region. Bootstrapped response functions showed that annual growth was mainly influenced by May to June temperatures in pine and by June to July temperatures in spruce and larch. Spruce and pine chronologies showed high positive correlations with previous October temperature. June–July temperatures were reconstructed based on spruce (1795–1996) and larch (1615–1999) tree ring chronologies. The pine chronology could not be used for a reliable temperature reconstruction, due to low values of explained May–June temperature variance (11–15%) but the species has a high potential to help clarify the May–June and October climatic influence on ring width observed in all three species. We explained the effect of the early vegetation period (May–July) and the differences in the temperature signals between spruce and larch tree ring chronologies with the influence of previous September and October temperature on tree growth with the warming effect of the Ob River and differences of the species’ photosynthetic possibilities and the activity of chloroplasts and bud meristem tissues.     

Heterorhabditis sp. (Nematoda: Heterorhabditidae): A Nematode Parasite Isolated from the Banded Cucumber Beetle Diabrotica balteata

A nematode identified as Heterorhabditis sp. was discovered in June 1982 in larval cadavers of the banded cucumber beetle, Diabrotica balteata, in soil on wooded land. Effective beetle control (over 95%) was obtained when larvae were exposed to potted soil containing infective stage nematode juveniles or infected larval cadavers. The nematode was propagated in vivo on larvae of D. balteata, Diaphania nitidalis (the pickleworm), and Galleria mellonella (the greater wax moth). This Heterorhabditis sp. has promising potential as a biocontrol agent for the banded cucumber beetle.     

Development of a nuclear polyhedrosis virus in midgut cells and penetration of the virus into the hemocoel of the armyworm,Pseudaletia unipuncta

The development of a nuclear polyhedrosis virus (NPV) in larval midgut cells of the armyworm, Pseudaletia unipuncta, is similar to that of other NPV. In the nucleus, the envelopes around the nucleocapsids seem to be derived de novo or from the inner layer of the nuclear envelope wich forms cisternae, blebs, or infoldings. The nucleocapsids are also enveloped by synhymenosis during passage through the nuclear membrane, the cell membrane, or the endoplasmic reticulum membrane. Both enveloped and unenveloped nucleocapsids may enter the cytoplasm through the nuclear pore or budding through the nuclear membrane. From the cytoplasm the virions may enter the hemocoel through the basal cell and basement membranes or through the endoplasmic reticulum, intercellular space, and the basement membrane.     

Apis iridescent virus and "clustering disease" of Apis cerana

NPV of Spodoptera littoralis was completely inactivated in vitro following 10 min of exposure to a temperature higher than 90°C, but survived 3 weeks at ?20°C. At pH 12, some 75% of the infectivity was lost. Measurable proteolysis in vitro of the polyhedral protein by a larval midgut extract could be obtained only when the pH of the reaction mixture was raised to an unnatural level of 10.5, the natural pH of the midgut content being 8.5 or 9.5 according to different authors. The plant growth retardant Phosfon synergized mortality caused by the NPV. The virus could be cross-transmitted to two congeneric species of Spodoptera (S. exigua and S. litura), but could not infect any of four tested species belonging to other genera of the Moctuid family.     

Studies on the application of a nuclear polyhedrosis virus to control populations of the Egyptian cottonworm, Spodoptera littoralis

Variations in the resistance to nuclear polyhedrosis virus (NPV) were found in three populations of Spodoptera littoralis. The LD₅₀ for the most resistant population was 1.07 × 10⁴ PIB/5th instar larva as compared to 8.4 × 10² and 5.8 × 10² PIB/larva in the other two populations. The effect of NPV persisted in larvae which survived and pupated. Some of the pupae died, and those which survived produced normally shaped adults. While fecundity was sharply reduced in the less resistant populations, the effect on the most tolerant population was less pronounced. A 3-year-old inoculum, stored unprotected from daylight and without cooling, was much less effective even against the most sensitive larval population as compared to a relatively fresh and refrigerated batch. Larvae in their 6th instar proved to be approximately 10-fold more resistant to the NPV than 5th instar ones, while the difference in weight was only about twice. These variations in resistance to NPV are also discussed from the point of view of applying S. littoralis NPV in pest control schemes.     

Tree growth and climate sensitivity in open and closed forests of the southeastern Tibetan Plateau

The creation of forest openings is a frequently observed phenomenon in many types of forests. On the southeastern Tibetan Plateau, where the average elevation is greater than 4000 m above sea level, differences in tree growth between forest stands with openings and completely closed stands are poorly characterized. Here, we presented a dendrochronological study of Tibetan juniper (Juniperus tibetica Kom.) and Sikkim spruce (Picea spinulosa (Griff.) Beissn.) in an open and a closed stand, near Qamdo of eastern Tibet. We found that the growth of juniper responded to climate in a similar way in the open and closed stands, and was positively correlated with temperature from October to January and with the Palmer Drought Severity Index (PDSI) from September to June. In contrast, the growth of spruce responded to climate differently in the open and closed stands: growth was positively correlated with the PDSI from September to May in the open stand, whereas it was positively correlated to November and December temperatures (of the prior year) and current June temperature in the closed stand. Interannual variation in, and standard deviations among, juniper tree ring widths were similar in both stands for the past four centuries, whereas they differed in spruce over the past two centuries, particularly in the 1900s. These results suggest that juniper tree ring growth is less sensitive to stand structure than that of spruce, thus providing more reliable climate signals. The data obtained from our study will help forest managers understand the ecology of juniper and spruce in open and closed stands and are therefore useful for management planning.     

Parelaphostrongylus odocoilei: Life cycle in experimentally infected cervids including the mule deer, Odocoileus h. hemionus

The life cycle of a metastrongyloid nematode, Parelaphostrongylus odocoilei, was successfully completed in three members of the Cervidae: mule deer (Odocoileus h. hemionus), black-tailed deer (O. h. columbianus), and moose (Alces alces andersoni). The terrestrial gastropod, Triodopsis multilineata, was the experimental intermediate host. White-tailed deer (O. virginianus dacotensis) were refractory to infection. The prepatent period of P. odocoilei was significantly shorter in mule deer (X = 53 days) than in the black-tailed deer or moose. There was an inverse relationship between the size of the infective inoculum and the duration of the prepatent period of P. odocoilei in mule deer, but not in black-tailed deer. The duration and intensity of larval production of P. odocoilei were higher in mule deer than in the other hosts. Peak larval production in the feces (approximately 14,000 larvae/g) of mule deer was in excess of previous reports for elaphostrongyline nematodes, regardless of the size of the infective inoculum. Daily larval production, estimated at 3 to 4 × 10⁶ larvae/day, was six times higher than estimates for other elaphostrongylines. The duration of patency was not clearly established, but three mule deer and one black-tailed deer passed larvae for 12, 18, 24, and 18 months, respectively. On the basis of the reduced prepatent period and increased length and intensity of larval production, O. h. hemionus is considered the primary host of P. odocoilei.