P.V. Vail

Reciprocal infectivity of nuclear polyhedrosis viruses of the cabbage looper and alfalfa looper

The cross-infectivity of two distinct nuclear polyhedrosis viruses, one isolated from the cabbage looper, Trichoplusia ni, which has the virions embedded singly in the polyhedral matrix; and one isolated from the alfalfa looper, Autographa californica, in which the virions are embedded multiply, was investigated. The multiply embedded virus was at least four times more pathogenic than the singly embedded virus to the cabbage looper and was also highly infective to the alfalfa looper. In contrast, the singly embedded cabbage looper virus was less infective to both the original and the alternate hosts. Cross-infectivity of the viruses was confirmed with both light and electron microscopes.

Replication and infectivity of the nuclear polyhedrosis virus of the alfalfa looper, Autographa californica, produced in cells grown in vitro

Abstract A virus isolated from the alfalfa looper, Autographa californica, replicated successfully and rapidly in a suspended ovarian cell line of the cabbage looper, Trichoplusia ni. Polyhedra were observed in the nucleus of cells within 20 hr after inoculation. The cytopathological changes typical of nuclear polyhedrosis infections were observed, and an average of 64 polyhedra/cell were produced. These polyhedra were quantitatively as infectious to cabbage looper larvae as those produced in vivo. In addition, they were infective to Heliothis virescens, Pectinophora gossypiella, Spodoptera exigua, A. californica, and Anagrapha falcifera.

Sodium hypochlorite and formalin as antiviral agents against nuclear-polyhedrosis virus in larvae of the cabbage looper.

Abstract Experiments were conducted to determine the effectiveness of sodium hypochlorite and formaldehyde in preventing infections of nuclear-polyhedrosis virus in larvae of the cabbage looper, Trichoplusia ni. Sodium hypochlorite was effective as an egg surface sterilant; formalin was effective as an egg wash and as a prophylactic when low concentrations were incorporated into the semiartificial rearing medium. The biological effects on the host insect were also investigated. In bioassays, the biological activity of suspensions of polyhedral inclusion bodies was reduced when formaldehyde was used in the medium; both ld 50 and lt 50 values were increased by the presence of formalin (formaldehyde solution).

Infectivity of a nuclear polyhedrosis virus from the alfalfa looper, Autographa californica, after passage through alternate hosts☆☆☆

Abstract A nuclear polyhedrosis virus isolated from the alfalfa looper, Autographa californica, was found to infect several species of caterpillars including the cabbage looper, Trichoplusia ni; the beet armyworm, Spodoptera exigua; and the saltmarsh caterpillar, Estigmene acrea. Studies were therefore conducted to determine the quantitative effects of passage through the alternate hosts, S. exigua and E. acrea, on the infectivity of this virus to newly hatched first-instar cabbage looper larvae. When 11 preparations of polyhedra obtained from a like number of primary passages through the original or alternate hosts were assayed and the mortality at 7-, 10-, and 14-day intervals were subjected to probit analysis, the LD50 s for the three intervals differed but those for the preparations at any given interval did not. Therefore, any of the three hosts could be used to propagate the virus, and whichever proves the easiest to rear and provides the highest yields of polyhedra can be selected.

The influence of infections of nuclear-polyhedrosis virus on adult cabbage loopers and their progeny

Abstract The longevity, mating, and oviposition of adult cabbage loopers ( Trichoplusia ni ) infected with nuclear-polyhedrosis virus were not affected, even when high titers of virus were used; infection occurred only when the virus was injected into the hemocoel. Histological examination of diseased adults revealed infected nuclei in the tracheal matrix cells but rarely in the fat body, hypodermis, or other tissues that are infected at the larval stage. Viability of eggs was significantly reduced (to less than 10%) the first few days after treatment when 1-day-old female moths were injected with the virus, but this effect decreased with dilution. Also, the effect was less when the female was older at the time of infection. Examination of dead eggs showed that embryological development had commenced. The large numbers of progeny reared from moths that were injected with the virus rarely showed infection, indicating that transovarian transmission of the virus did not occur. In contrast, progeny of moths fed the polyhedra were often infected though the effect was unpredictable and could be eliminated by surface-sterilization of the eggs.

An RNA virus in Autographa californica nuclear polyhedrosis preparations: Detection and identification

Abstract A 35-nm RNA virus of Trichoplusia ni (TRV) was detected in preparations of Autographa californica nuclear polyhedrosis virus (AcMNPV). In comparisons of methods of detection of TRV (gel electrophoresis, sucrose density gradient centrifugation, and serology), the enzyme-linked immunosorbent assay (ELISA) was the most sensitive method for quantitative detection of the contaminant virus in infected larvae and AcMNPV preparations. A scheme is proposed for the detection of contaminant viruses in NPVs being developed for biological control.

An RNA Virus in Autographa californica Nuclear Polyhedrosis Virus Preparations: Gross Pathology and Infectivity

Abstract The pathology and infectivity of an RNA virus infectious to Trichoplusia ni larvae was investigated. The enzyme-linked immunosorbent assay (ELISA) and weight depression were used as criteria for virus concentration in larval homogenates and live larvae, respectively. Infected larvae were severely stunted, weighing as little as 13 times less than uninfected individuals of the same age, yet appeared normal morphologically. The virus was found to cause only slight mortality at high concentrations. Infected larvae displayed the pathological stunting response down to a dose of 0.1 ng of virus. Larvae infected with doses 100 times lower did not show the weight response but such inapparent infections were detectable by ELISA. Because of these subtle gross pathological symptoms, particularly at low levels of infection, infected individuals could easily remain unde-tected in a group-reared colony.

Replication of the Autographa californica nuclear polyhedrosis virus in insect cell lines grown in modified media

Abstract When certain ingredients were eliminated from a medium used to culture a cabbage looper cell line that can support replication of Autographa californica nuclear polyhedrosis virus, cells grew successfully and could be serially transferred a minimum of 44 times. Also, they maintained their ability to support replication of the Autographa californica virus, and the polyhedra produced were as infectious as those from cells grown on the original medium. The cost of the least expensive medium that would support cell growth was 2.8 times less than the cost of normal growth medium.

The histopathology of a nuclear polyhedrosis in larvae of the cabbage looper, Trichoplusia ni, related to symptoms and mortality

Abstract A thorough histopathological study of larvae of the cabbage looper, Trichoplusia ni , infected with a nuclear-polyhedrosis virus revealed the relationship between the histological changes and the progression of external signs and symptoms. Although considerable variation occurred, even when the time of inoculation was controlled, all larvae contained polyhedra in the cells of susceptible tissues 72 hr later. An incubation period of 72 to 84 hr proved optimum for sampling and diagnosing the disease: at that time, the susceptible tissues were heavily infected though lysis of infected cells was minimum. Infected nuclei were found in the tracheal matrix, hypodermal, blood, and fat-body cells and also in and associated with muscle, Malpighian tubule, and nerve tissues.

Infectivity of Autographa californica nuclear polyhedrosis virus extracted with digestive fluids of Heliothis zea, Estigmene acrea, and carbonate solutions

Abstract The infectivity of nonoccluded virus from Autographa californica nuclear polyhedrosis virus inclusion bodies dissolved by digestive fluids or sodium carbonate in vitro was compared. Digestive fluids were collected from fifth-instar larvae of Heliothis zea and Estigmene acrea . Sodium carbonate solutions were used at mean p Hs equal to that of each of the respective fluids of both insect species. Infectivity to TN-368 cells was greatest after short-term exposure to digestive fluids of both insect species and was greatest after long-term exposure to both solutions of carbonate. There was little or no infectivity with heat-treated digestive fluids.