The comparative susceptibilities of Pieris brassicae and P. rapae to a granulosis virus from P. brassicae

A comparison was made of the dosage-mortality responses of larvae of Pieris brassicae and P. rapae to infection by P. brassicae granulosis virus (GV). Bioassays with first, second, third, and fourth-instar larvae of both species revealed a marked difference in susceptibility between instars and between species. Median lethal dosages (LD₅₀s) for P. rapae larvae ranged from five capsules for the first instar to 662 capsules for the fourth instar. With P. brassicae, this range extended from 66 capsules to 2.3 × 10⁷ capsules. The time-mortality responses of the two species were similar when fed virus dosages equivalent to an LD₉₀. Median lethal times (LT₅₀s) ranged from 5 days for first-instar larvae to 7–8 days for fourth-instar larvae. A comparison between a long-established laboratory stock of P. brassicae and a stock recently acquired from the field showed no significant difference in their susceptibility to GV. The implications of the pronounced species differences in susceptibility to GV infection are discussed in relation to the potential field control of P. rapae and P. brassicae.     

Production and field evaluation of codling moth granulosis virus for control of Cydia pomonella in the United Kingdom

Codling moth granulosis virus (Cp GV) was produced in larvae of Cydia pomonella reared on artificial diet. The average yield of virus (9 × 10⁹capsules/larva) was increased by raising the larvae on diet containing methoprene, a juvenile hormone analogue. In field trials in 1978 and 1979, one or two high-volume applications of Cp GV at 7 × 10¹⁰ capsules/litre achieved reductions in numbers of mature larvae and damaged fruit that were little different from those obtained by two applications of azinphos-methyl. A field trial in 1980 showed that at concentrations of Cp GV ≥ 6 × 10⁸ capsules/litre, damaged diminished slowly with increasing virus concentration. Following virus application in 1980, Cp GV infectivity was reduced by half in 3 days, but some activity persisted at least 4–8 wk after spraying. The results indicate that codling moth GV is an effective control agent particularly in reducing numbers of larvae and the more severe forms of fruit damage.     

Histopathology and bioassay of Plathypena scabra granulosis virus

A granulosis virus was found infecting Plathypena scabra larvae in Iowa. The capsules averaged 377 ± 25 × 222 ± 19 nm. On the basis of light microscopical observations, the virus appeared to infect the epidermis, fat body, and tracheal matrix cells. The LC₅₀ and LC₉₅ were 6.7 × 10⁷ and 1.5 × 10⁹ capsules/acre, respectively. The LT₅₀ values varied from 3 to 9 days for 1 × 10¹² and 1 × 10⁸ capsules/acre, respectively.     

The susceptibility of the pea moth, Cydia nigricana, to infection by the granulosis virus of the codling moth, Cydia pomonella

Laboratory studies demonstrated that neonate larvae of the pea moth, Cydia nigricana, are susceptible to infection with a granulosis virus (CpGV) isolated from the codling moth, Cydia pomonella. Comparative LC₅₀ values for C. nigricana and C. pomonella are 1.90 × 10⁵ and 1.54 × 10⁴ capsules/ml of diet, respectively. The virus extracted from CpGV-infected pea moth larvae is serologically related, and probably identical, to CpGV.     

Interaction between the tachinid parasite,Sturmiopsis inferens and granulosis virus in the sugarcane shoot borer,Chilo infuscatellus [Lep.: Crambidae]

Competition between granulosis virus (GV) and the larval parasite,Sturmiopsis inferens Tns. (Tachinidae: Diptera), was studied in 3^rd — and 4^th — instar larvae of the sugarcane shoot borer,Chilo infuscatellus Snellen (Crambidae: Lepidoptera), under laboratory conditions. Mortality due to GV infection and parasitization was 76.8 and 47.6 per cent, respectively, when they were tested separately. But when hosts were infected simultaneously with microfeeding of GV and larval parasite, a significantly low parasitism (5.5%) was obtained compared to 74.8 per cent mortality by GV infection. When the larvae were microfed with the GV 6 days after inoculation with parasitic maggots, mortality due to the virus was reduced significantly to 20.5 per cent, but when the maggot inoculation was preceded by virus microfeeding 6 days before, parasitization was unsuccessful, while 75% of larvae died of virus. Results obtained from field — collected larvae also showed that significantly more parasite puparia were recovered from healthy larvae than from virus — infected larvae. Similar differences in parasitization were not obtained in the case of healthy or virus — infected pupae.      

The storage of infective spores of Vairimorpha necatrix (Protozoa: Microsporida) in antibiotic solution at 4 degrees C.

The interactions between the Diacrisia virginica granulosis virus (DGV) and the Hyphantria cunea baculovirus isolates were determined, utilizing defined differences between the time-mortality responses of these viruses fed to H. cunea larvae. The DGV, having a prolonged incubation period, when given an advantage in time or in the number of capsules, was able to prevent the expression of the more lethal H. cunea granulosis virus (HcGV) isolate. The time-mortality response of test larvae simultaneously fed equivalent dosages of HcGV and DGV was intermediate to that achieved with HcGV alone or DGV alone. Larvae infected with the DGV isolate were still susceptible to double infection by the nucleopolyhedrosis virus. The time-mortality response demonstrated that the development of nucleopolyhedrosis was only partly inhibited by preinfecting the test larvae with the DGV isolate.     

Control ofAgrotis segetum [Lep.: Noctuidae] root crops by granulosis virus

Agrotis segetum Schiff. granulosis virus (GV) propagated in Danish laboratory cultures was applied against field populations ofA. segetum in experimental latin square plots planted with beetroots, carrots and potatoes. Some test plots were isolated by net tents extending 15 cm into the soil whereas others were not caged. Plots were treated with suspensions of GV containing 10⁶ to 10⁸ capsules per ml with 50 ml being applied per m² of plot. In 4 tests in which released eggs or larvae were caged over plots, cutworm numbers and damage were reduced by approximately 80% compared to untreated plots. The comparable reductions in 3 open experiments with natural populations of cutworms were 65–75%. GV-treatment 4 days after release of eggs appeared to be more effective than treatment 10 days after release. Whereas treatments with 10⁷ and 10⁸ capsules per ml reduced damages to approximately 75%, the effect of 10⁶ Capsules was only 50%. Damage reduction by treatment with parathion varied from 50% in 2 caged experiments to approximately 20% in 2 open experiments, indicating that parathion was less effective than GV. The data indicated a residual effect of GV from one year to the next. Furthermore GV appeared to have spread at least 10 m from foci of application.     

Field evaluation of a granulosis virus for control ofPieris rapae [Lep.: Pieridae] in the United Kingdom

A purified granulosis virus isolated fromPieris brassicae (L.) was tested in the field against an introduced population ofPieris rapae (L.) larvae on cabbage (cv January King) in small experimental plots at Littlehampton, Sussex. Experiments were designed to compare the relative efficacy of single and multiple applications of virus (2.1×10¹² and 3.7×10¹² or 2.1×10¹⁴ and 3.7×10¹⁴ virus capsules/ha) in reducing numbers ofP. rapae larvae. An experiment was carried out in June 1978 and repeated in August to coincide approximately with the 2 natural generations ofP. rapae in southern England. Larval populations were monitored by regularin situ assessment of plants and by destructive sampling. Within 10 days of spraying virus there was a significant reduction in the mean larval population on all virus-treated plots compared with untreated controls. Sprays of 2.1×10¹⁴ and 3.7×10¹⁴ capsules/ha reduced larval numbers more quickly than 2.1×10¹² and 3.7×10¹²/ha treatments. In the 1st experiment, three sprays of virus at either 2.1×10¹² or 2.1×10¹⁴ capsules/ha gave no increase over the final level of control achieved by a single spray. However, in the 2nd experiment, a single spray of 3.7×10¹² capsules/ha did not significantly reduce the numbers of larvae. It is likely that this failure could be accounted for by a combination of the larger “natural” population ofP. rapae recorded midway through the 2nd experiment and the rapid inactivation of virus deposits which left little infectious virus to infect these larvae. Virus inactivation was so rapid that only 7–33 % of the initial virus deposits remained 1 day after application. These results suggest that further understanding of virus formulation, persistence and dosage rates are needed before such a virus can be used in a rational manner.     

Susceptibility of Hyphantria cunea to a granulosis virus isolated from Diacrisia virginica

The dosage-mortality response of Hyphantria cunea larvae to a granulosis virus isolated from Diacrisia virginica was studied. Serial decimal dilutions of the D. virginica granulosis virus were fed to early second-instar H. cunea larvae. the LD₅₀ for this virus (7.9 × 10⁵ capsules/larva) was significantly greater than the LD₅₀ calculated for the H. cunea granulosis virus (7.06 × 10⁴ capsules/larva) against the same instar of H. cunea. Time mortality studies demonstrated that the LT₅₀ values for the D. virginica granulosis were four to six times greater than for comparable dosages of H. cunea granulosis virus. Based on the mortality response of assayed H. cunea, it is possible to distinguish between the D. virginica granulosis virus and the H. cunea granulosis virus.     

A Comparison of the Efficacy of Nuclear Polyhedrosis and Granulosis Viruses in Spray and Bait Formulations for the Control of Agrotis segetum (Lepidoptera: Noctuidae) in Maize

Agrotis segetum nuclear polyhedrosis virus (AsNPV) and granulosis virus (AsGV), propagated in laboratory cultures of A. segetum in England and A. ipsilon in Spain, respectively, were applied to plots of maize plants at the one‐ to four‐leaf stage of growth. Plots were arranged in a 6 x 6 Latin square design and infested with second‐instar A. segetum larvae (the common cutworm). Each virus was applied in separate treatments by two application methods; as an aqueous spray containing 0.1% Agral as a wetting agent, and as a bran bait. The NPV was applied at a rate of 4 X 10¹² polyhedra/ha, and the GV at 4 X 10¹³ granules/ha. Soil and plants were sampled for larvae on three occasions following virus treatment: 24 h, 4 days and 11 days. The larvae were reared on diet in the laboratory, until death or pupation, to examine the rate and level of viral infection. Infection data showed 87.5% and 91% NPV infection and 12.5% and 55% GV infection in spray and bait treatments, respectively, in larvae sampled 24 h after treatment. In larvae sampled 4 days after treatment, the results were 78% and 100% NPV infection, and 13% and 6% GV infection. A total of only six larvae were retrieved on day 11. In both treatments larvae infected with AsNPV died significantly more rapidly and at an earlier instar than those infected with AsGV, indicating that AsNPV appears to have better potential as a control agent for A. segetum.     

Pathogenicity of entomopathogenic fungus,Metarhizium anisopliae MET-GRA4 isolate on dengue vectors,Aedes albopictus and Aedes aegypti mosquito larvae (Diptera: Culicidae)

Considering the rapid transmission of the dengue virus, substantial efforts need to be conducted to ward-off the epidemics of dengue viruses. The control effort is depending on chemical insecticides and had aroused undesirable conflicts of insecticide resistance. Here, we study the entomopathogenic fungus, Metarhizium anisopliae as a promising new biological control agent for vector control. The pathogenicity effects of Metarhizium anisopliae against field and laboratory strains of Aedes albopictus and Aedes aegypti larvae were tested using the larvicidal bioassay technique. The results demonstrate that the treatments using M. anisopliae isolate MET-GRA4 were highly effective and able to kill 100% of both Ae. albopictus and Ae. aegypti mosquito larvae at a conidia concentration of 1 × 10?/ml within 7 days of the treatment period. The fungus displayed high larvicidal activity against laboratory and field strain of Ae. aegypti larvae with LC₅₀ values (9.6 × 10³/ml, 1.3 × 10³/ml) and LC₉₅ values (1.2 × 10?/ml, 5.5 × 10⁵/ml) respectively. For Ae. albopictus, LC₅₀ values for laboratory and field strains were (1.7 × 10⁴/ml, 2.7 × 10⁴/ml) and the LC₉₅ values were (2.1 × 10?/ml, 7.0 × 10⁵/ml) respectively. Interestingly, the susceptibility of field strain towards M. anisopliae was higher as compared to the laboratory strain Aedes larvae. In which, the causative agents of all the dead larvae were verified by the virulence of M. anisopliae and caused morphological deformities on larval body. The findings from this study identify this isolate could be an effective potential biocontrol agent for vector mosquitoes in Malaysia.     

Bioassay of a nucleopolyhedrosis virus of the gypsy moth, Porthetria dispar

The pathogenicity of an American isolate of the nucleopolyhedrosis virus of Porthetria dispar was studied. Laboratory data on third-instar larvae showed that mortality was directly related to virus concentration. The computed LD₅₀ was 1,729 PIBs/larva or 72 PIBs/mg larval body weight. The LT₅₀'s for 2.5 × 10⁶, 2.5 × 10⁵, 2.5 × 10⁴, 5 × 10³, and 2.5 × 10³ PIBs/larva were 8.1, 9.9, 11.3, 12.2, and 13.1 days, respectively. Approximately 37 and 60% of the total larval mortality occurred during the third- and fourth-instar, respectively. The periods to pupation and the pupal weights of survivors apparently were not affected by virus concentration. Moth emergence from surviving pupae was not reduced.     

Serological study on the transmission of a granulosis virus of the armyworm,Pseudaletia unipuncta (Lepidoptera: Noctuidae), to other lepidopterous species

The synergistic (Hawaiian) strain of a granulosis virus (GV) from the armyworm, Pseudaletia unipuncta, was transmitted to Spodoptera exigua, Autographa californica, and Trichoplusia ni. The viruses isolated from these hosts were tested by radial double-immunodiffusion (RDD) and immunoelectrophoresis (IE) for their relationship to the original virus. Untreated and heat-treated virus inclusion bodies (capsules) were compared for their antigenic properties but no differences were detected. The antiserum elicited against the whole capsule was more sharply specific for the antigenic determinants than the one elicited against the dissolved capsule proteins. The viruses obtained from S. exigua and T. ni elicited precipitin lines that differed from those of the P. unipuncta GV in their electrophoretic mobility with the one-trough IE method; however, with the two-trough method, the lines fused indicating that the antigens were identical. The major precipitin line indicating identity of the viruses wasthat produced by the synergistic factor (SF) purified from the capsule proteins of the synergistic GV strain. The presence of SF in the GV produced in alternate hosts indicated that its production was virus directed. The SF was not detected in the GVs of Laspeyresia pomonella and Pieris rapae and in the nonsynergistic Oregonian GV of P. unipuncta. A field-collected GV from S. exigua exhibited a different precipitin pattern from that of the synergistic GV, but one of the precipitin lines shared partial relationship to the SF.     

Comparative analysis of the alkali-liberated components of the Hyphantria cunea and the Diacrisia virginica granulosis viruses

The biochemical and biophysical characteristics of the closely related Diacrisia virginica and Hyphantria cunea granulosis virus isolates were examined. Sucrose gradient sedimentation patterns of alkali-solubilized DGV and HcGV capsules were identical. The top, middle, and bottom fractions from either viral isolate were infectious when injected into susceptible host larvae. Electrophoretic analysis of alkaline-solubilized granulin extracts demonstrated that both viruses contain alkaline proteolytic activity. The major granulin protein (～28,000 daltons) of both isolates comigrated in a SDS-PAGE. Electrophoretic separation of the virus proteins demonstrated some quantitative differences between the two granulosis viruses. The enveloped nucleocapsids and the nucleocapsids of the two viruses were morphologically indistinguishable.     

Dosage-mortality and time-mortality studies of a granulosis virus in a laboratory strain of the codling moth,Laspeyresia pomonella

Different doses of a granulosis virus were administered to first- and fifth-instar larvae of the codling moth Laspeyresia pomonella. Virus was very pathogenic for both larval instars. The LD₅₀ values for first- and fifth-instar larvae were 5 and 49 capsules/larva, respectively. However, fifth-instar larvae were much more variable in their response to virus than first-instar larvae. Using probit methods it was calculated that 1 capsule could cause death in about 25% of both larval instars but 1578 capsules were required to cause 70% mortality of fifth-instar larvae as compared to 12 capsules for first-instar larvae. This is the first report of a decided difference in variability of response to virus by two larval instars of the same species. A bimodal response by both larval instars was observed in time-mortality studies. Apparently, about 20% of the larvae were very resistant to virus infections.     

The mode of transmission of Tipula iridescent virus: I. Source of infection

A virus was isolated from a diseased tipulid larva and identified as Tipula iridescent virus (TIV) on the basis of the size and morphology of the virion, the production of iridescence in vitro and in infected tipulid larvae, and a serological reaction between antiserum against the virus and an isolate of TIV.A stock of Tipula oleracea was bred in the laboratory. Subjection of larvae to several stress factors did not result in any evidence for activation of a latent virus. Healthy T. oleracea larvae did not develop iridescence when confined in petri dishes with either live TIV-infected larvae or with large amounts of their feces, although these feces were found to contain infective virus by injecting extracts into healthy larvae. It appears that the concentration of virus in the feces of infected larvae is not high enough for them to serve as a source of infection. It was shown that the cadavers of TIV-infected larvae can serve as a source of infection for healthy first- and fourth-instar larvae.     

Effect of larval age and dosage of nuclear polyhedrosis virus on the susceptibility of diamondback moth, Plutella xylostella

A laboratory experiment was conducted to study the efficacy of nuclear polyhedrosis virus (NPV) with nine concentrations against all stadia of Plutella xylostella (L). The susceptibility of the larvae was correlated negatively with the period of development of the larvae and positively with the virus concentrations. The highest mortality of 84% was recorded in first stadium larvae compared to lowest mortality of 38% in fourth stadium larvae. The LC₅₀ was 5.5×10¹ and 4.0×10⁴ polyhedral inclusion bodies (PIB)/ml for first and fourth stadium larvae, respectively.     

Dosage-mortality and time-mortality responses of the armyworm Spodoptera exempta to a nuclear polyhedrosis virus

Third-instar Spodoptera exempta larvae were fed on young maize leaves treated with 20 μl of polyhedral inclusion body (PIB) suspension of concentrations that varied from 1.6 × 10² to 1.6 × 10⁹ PIBs/ml. Daily observations were kept on mortality rates. A probit analysis on the results gave an LD₅₀ value of 48.4 PIBs/larva (lower and upper fiducial limits 39.2 and 59.4 PIBs/larva, respectively), and an LT₅₀ that varied from 146.2 to 221.3 hr, depending on the dosage. LD and LT values obtained show the high pathogenicity of S. exempta nuclear polyhedrosis virus to its host.     

Isolation of a factor, from the capsule of a granulosis virus, synergistic for a nuclear-polyhedrosis virus of the armyworm

When the capsules of a granulosis virus are fed together with the polyhedra of a nuclear-polyhedrosis virus to larvae of the armyworm, Pseudaletia unipuncta, the former enhances the infectivity of the latter virus, a synergistic interaction. The enhancement of infectivity depends upon the concentration of the polyhedra and the capsules. The factor responsible for the synergistic activity in the capsule can be dissolved in alkaline solution, separated from the virus particles by centrifugation, and further purified by Sephadex G-200 gel filtration with 4 m urea. The fraction obtained from Sephadex filtration and containing the synergistic factor can be separated into two components by disc-electrophoresis with 8 m urea. Both components possess synergistic activity. The ID₅₀ of the synergistic factor corresponds to 0.0015 OD₂₈₀. Its optimum pH is 8.5. Synergism is most evident when the factor is fed to larvae together with the polyhedra or is fed 24 hr prior to the ingestion of the polyhedra. The factor appears to be a simple or a conjugated protein of the capsule.     

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.