S.Y. Young

Effect of dew from cotton and soybean foliage on activity of Heliothis nuclear polyhedrosis virus

Abstract The ionic composition of dew collected from foliage of cotton and soybean plants as well as its potential for inactivation of Heliothis NPV were compared. Cotton dew had a mean pH of 8.8 and was more alkaline than soybean dew (pH 7.8). Cotton dew had a higher concentration of ions that did soybean dew but there was no qualitative difference in the cation content of dew from the two hosts. In bioassay tests, no loss of activity occurred when polyhedra were held in dew of either plant species. If the dew in which polyhedra were suspended was air-dried and resuspended daily in deionized water, polyhedra in soybean dew remained active but in cotton dew retained little activity after 7 days. Also, electron microscopical examination of polyhedra pelleted from these cotton dew preparations showed much dissolution after 7 days. Although there was dissolution of polyhedra in cotton dew when dried, an examination of polyhedra on the upper surface of either plant species in the field showed little degradation after 7 days.

A newly isolated densonucleosis virus from Pseudoplusia includens (Lepidoptera: Noctuidae)

Abstract An icosahedral DNA virus isolated from the soybean looper, Pseudoplusia includens , was characterized. Purified virus had a diameter of 20 ± 1 nm and negatively stained preparations showed a trend to form linear to three-dimensional crystals. The virus had a sedimentation coefficient of 120 ± 3 S and a buoyant density of 1.40 ± 0.01 g/cm 3 . The DNA content of the virus was 37.8 ± 0.1% and the absorption spectrum showed it to be a typical nucleoprotein. Viral DNA in situ was shown to be single-stranded by staining the virus with acridine orange as well as by reaction to formaldehyde. Evidence of inverted terminal repetition of the DNA was observed by electron microscopy. The terminal repetition comprises ca. 6–7% of the genome. The molecular weight of the ssDNA was 2.0 ± 0.1 × 10 6 as determined by agarose gel electrophoresis or 2.1 ± 0.1 × 10 6 as determined by electron microscopy. Four virion proteins with molecular weights of 46.5 ± 0.1, 54.0 ± 0.1, 64.0 ± 0.2, and 87.0 ± 0.1 × 10 3 were detected by 9% SDS-polyacrylamide gel electrophoresis. Double-diffusion tests showed the virus to be serologically related but not identical to DNV-1. Ultrathin sections showed that the nucleus of the hemocyte, muscle, hypodermal, and fat body cells contained virus-like particles. The chromatin of an infected nucleus always underwent a margination and the nucleoplasm was often replaced largely by virions. Data indicate that the virus belongs to the Densovirus of the family Parvoviridae.

Effect of nuclear polyhedrosis virus infection in Spodoptera ornithogalli larvae on post larval stages and dissemination by adults

Nuclear polyhedrosis virus (NPV) infection in fourth-instar yellow striped armyworm, Spodoptera ornithogalli (SoNPV), larvae had little effect on individuals that survived to post larval stages. Pupal mortality, pupal sex ratio, days in the pupal and adult stages, and egg fertility were not altered by the disease. Fecundity, however, was significantly reduced in moths that had survived the viral disease as larvae (P < 0.05). Survivors did not transmit the disease to progeny, but when the virus was applied to the body surface of females by any of several methods the disease was spread to progeny in the laboratory and in field-caged soybean. Transmission by contaminated females in oviposition cages in the laboratory differed by the method of contamination. Mortality in progeny was highest (77.3%) when moths were wetted with 0.005% sodium dodecyl sulfate and dusted with 1010 polyhedral inclusion bodies per gram of SoNPV. Mortality of progeny decreased as the time moths were held in the oviposition cage increased and with moth activity prior to placing them in the oviposition cage. Viral infection was much lower in progeny on field-caged soybean with the mean mortality from SoNPV varying with the method of moth contamination from 3.3 to 19.6%.

Some factors involved in the dissolution of Autographa californica nuclear polyhedrosis virus polyhedra by digestive fluids of Trichoplusia ni larvae

Abstract Factors involved in the dissolution of polyhedra of Autographa californica nuclear polyhedrosis virus (AcNPV) by digestive fluid collected from fifth stage Trichoplusia ni larvae were studied in vitro. Observations were made at timed intervals using phase contrast microscopy and transmission electron microscopy. When digestive fluid was heated at 50°C proteases retained activity. Exposure of polyhedra to digestive fluid previously heated to 50°C resulted in polyhedral matrix dissolution and envelope disruption in a manner similar to that of unheated digestive fluid, only delayed slightly. After exposure of polyhedra for 3 min, only enveloped virons were observed. Heating the digestive fluid to 60° or higher inactivated the proteases and altered the effect on polyhedra. Dissolution of the occlusion body matrix occurred but the polyhedral envelope remained and only a few weakened areas were observed in its structure. Within the polyhedral envelope, enveloped virons were not observed, only nucleocapsids and capsids. Exposure of polyhedra to 0.1 m sodium carbonate buffer at p Hs of 9.5 or higher had effects similar to those of the digestive fluid with heat (60°C)-inactivated proteases. The addition of trypsin and chymotrypsin to the 0.1 m sodium carbonate buffer had no effect, while the addition of a bacterial protease ( Streptomyces griseus ) at p Hs of 9.5 or higher resulted in dissolution of the matrix and disruption of the polyhedral envelope like the digestive fluid. Material infectious to TN-368 cells was obtained by exposure of AcNPV to T. ni digestive fluid. Maximum infectivity resulted from a 5-min exposure to unheated digestive fluid, with a dramatic decrease in infectivity with longer exposure. Exposure to digestive fluid with heat (60°C)-inactivated proteases resulted in a slower release of infectious material from the occlusion body, with a steady increase in the level of infectivity throughout the 30-min digestion period.

Influence of the host plant on occluded virus production and lethal infectivity of a baculovirus

Intra- and inter-specific effects of cotton, soybean, and clover on the time until death of Helicoverpa zea (Boddie) and Heliothis virescens (F.) larvae lethally infected with H. zea nucleopolyhedrovirus (HzSNPV) were evaluated in the laboratory. In the first test, on second instar only, the time until death of lethally infected larvae of both species differed with the plant tissues (vegetative or reproductive) and plant species. The total viral activity produced per larva in LC(50) units (occluded viral bodies (OBs) per larva/LC(50) in OBs/mm(2) of diet surface) was greater from H. virescens larvae fed vegetative than reproductive tissues of all host plants, but from H. zea virus production was greater only when fed vegetative tissue of soybean. In a second test that compared second and fourth instar H. virescens on cotton, total viral activity from larvae treated in both instars was greater when fed vegetative than reproductive tissues. Results of these tests suggest that the ability of host plants to influence baculovirus disease is more complex than previously believed. When examining the epizootic potential of a baculovirus, more attention must be given to the effects of the host plant on the insect-virus interactions.

Serological relationships of five nuclear polyhedrosis viruses from lepidopterous species

Abstract The serological relationships of five nuclear polyhedrosis viruses (NPV) were investigated using the immunodiffusion technique with intragel absorption. Reciprocal tests demonstrated that virion fractions from Autographa californica multiple embedded virus (MEV), Heliothis armigera MEV, and H. zea single embedded virus (SEV) are not related to each other or to virions from Trichoplusia ni SEV and Pseudoplusia includens SEV. Virion fractions of T. ni and P. includens NPV were shown to be closely related, sharing several antigens. Matrix fractions possessed a common group antigen and one or two antigens specific for the individual NPV with the exception that T. ni and P. includens NPV shared one of these antigens. The specific antigens of the matrix fraction were also shared with the homologous virion fraction.

Characterization of a picornavirus isolated from Pseudoplusia includens (Lepidoptera: Noctuidae)

Abstract Some properties and electron microscopy of an icosahedral RNA virus isolated from the soybean looper, Pseudoplusia includens , have been studied. The virus particles were 25 ± 1 nm in diameter, their sedimentation coefficient was 178 ± 4.2 S. and their buoyant density was 1.37 ± 0.01 g/cm 3 . The RNA content was 37.9 ± 0.2% and the RNA was single stranded with a poly(A) track. The virus capsid contained three major proteins with molecular weights of 30.0 ± 0.8, 31.0 ± 0.9, and 34.0 ± 1.1 × 10 3 , and two minor proteins with molecular weights of 33.0 ± 1.2 and 38.0 ± 1.1 × 10 3 . One genome component was detected with molecular weight 3.3 ± 0.1 × 10 6 . Agarose gel diffusion tests showed this virus has partial identity with cricket paralysis virus. Victoria strain. Electron microscopy revealed that high concentrations of virus particles were present in the midgut epithelial cells. Virus particles present in the lumen adjacent to these midgut epithelial cells appeared to have moved to the lumen from these cells. Virus particles could also be observed in the epidermal cells. Accumulations of microtubule and fibril containing vesicles in these cells appear to be due to the virus infection. It is proposed that this virus be included in the family Picornaviridae.

Dissolution of Autographa californica nuclear polyhedrosis virus polyhedra by the digestive fluid of Trichoplusia ni (Lepidoptera:Noctuidae) larvae☆☆☆

Abstract The dissolution of polyhedra of Autographa californica nuclear polyhedrosis virus by digestive fluid collected from 5th stage Trichoplusia ni larvae was studied in vitro. Observations were made at timed intervals using phase contrast microscopy, and scanning and transmission electron microscopy. Dissolution occurred rapidly and in a detectable sequence. Under phase contrast, most polyhedra lost their refringence by 0.5 min. The polyhedra became rounded in appearance with small protuberances on the surface and Brownian movement was observed within. After 1 min, the envelope of most polyhedra had ruptured, releasing the enclosed virions. The protuberances were also observed under the scanning electron microscope after digestion for 0.5 min. Many shell fragments devoid of internal contents were seen after more lengthy digestion. Internal structural changes were revealed by electron microscopy. After 1 min of exposure, polyhedra were observed in all stages of dissolution. By 3 min, only virions, scattered about in heterogeneous material, could be distinguished.

Nuclear polyhedrosis virus-infected and healthy anticarsia gemmatalis larvae as prey for Nabis roseipennis adults in the laboratory

Abstract Nabis roseipennis adults were tested to determine the suitability of healthy and nuclear polyhedrosis virus-infected Anticarsia gemmatalis larvae as prey. The rate at which N. roseipennis preyed upon larvae of the same size was comparable for uninfected and 2-day-infected larvae when the predator was placed in a Petri dish with a single larval prey. A significantly faster rate of attack was observed when larval prey in late stages of disease (4-day-infected) were third, fourth, or fifth instars, but not when they were second instars. When offered a choice between an uninfected and 4-day-infected larva in a Petri dish, N. roseipennis showed a preference for the diseased prey when the larvae were larger than second instar.

Cytopathology of the soybean looper, Pseudoplusia includens, infected with the Pseudoplusia includens icosahedral virus☆☆☆★

Abstract Ultrastructural responses of soybean looper cells of various tissues infected with Pseudoplusia includens icosahedral virus (PIIV), a newly characterized RNA virus [ Y. C. Chao, H. A. Scott, and S. Y. Young (1983) J. Gen. Virol. 64, 1835–1838], were studied in situ. Most cells of fat body and epidermis consistently contained virus particles and associated cytopathic structures. Virus particles, corresponding to those of purified PIIV in morphology and size, always occurred in the cytoplasm either in membrane-bound virogenic stroma and/or freely in the ground cytoplasm. Virogenic stroma, which appeared to be distinct from those induced by other insect viruses, consisted of electron-dense matrix material, in which virus particles were embedded, and membranous vesicles, 70 or 80 nm in diameter, containing nucleic acid-like fibrils. Virus particles in virogenic stroma occurred as hexagonally arranged crystalline arrays made up primarily of homogeneously dense particles, while those in the ground cytoplasm were dispersed randomly and had an electron-lucent central core. Extremely large numbers of virus particles were also located in noncellular cuticle layers of the integument.