Transmission of NPV in uniform- and mixed-age populations ofHeliothis zea [Lep: Noctuidae] on caged soybean

Transmission of a nuclear polyhedrosis virus (NPV) was examined in uniformaged and uniform- vs mixed-age populations ofHeliothis zea (Boddie) on caged soybean. Larval collections revealed viral disease outbreaks occurred in all treatments following release of infected larvae (Primary infected larvae). Transmission of NPV in uniform-aged populations was related to the density of primary infected larvae released in the population but not to the size at death of primary infected larvae (P<0.05). In mixed-age populations horizontal transmission in the oldest larvae in the population was equal to that in uniform-aged populations, providing that primary infected larvae in the mixed-aged population were all the age of the oldest noninfected cohorts. As the mixed-age population aged, transmission increased and was generally higher than that in the uniform-aged populations. Transmission was also higher when primary infected larvae were medium sized at death than when small or large at death. The concentration of virus deposited on foliage and in soil after all larvae had died on plants was related to density of primary infected larvae released. In soil, but not on foliage, the virus concentration was related to the size at death of primary infected larvae released. This material is based upon work supported in part by the U.S. Department of Agriculture under Agreement No. CRSR-2-1000.     

Resistance ofSpodoptera frugiperda [Lep.: Noctuidae] to a nuclear polyhedrosis virus in the field and laboratory

Median lethal doses (LD₅₀s) of nuclear polyhedrosis virus (NPV) were determined in neonatal offspring ofSpodoptera frugiperda (J. E. Smith) (Sf) larvae captured in southeastern Louisiana in 1981, 1982, and 1984. These LD₅₀s ranged from 1.8 to 16.3 polyhedral inclusion bodies (PIB)/insect. The LD₅₀s significantly (P<0.05) increased during the season of 1982 but had no pattern in 1981 or 1984. However, the Sf populations increased in heterogeneity of response to the NPV during all 3 years. The LD₅₀ increased from 4.1 to 18.7 PIB/insect in a Sf laboratory colony exposed to the NPV LD₈₀ for 7 generations, whereas in a control colony not exposed to NPV the LD₅₀ was 5.9 PIB/insect after 7 generations.     

Transmission agents of the nuclear polyhedrosis virus ofNeodiprion sertifer [Hym.: Diprionidae]

Colonies ofNeodiprion sertifer (Geoffroy) larvae infected by nuclear polyhedrosis virus were visited by parasitoids, predators, and scavengers. Six transmission pathways were studied in detail. Viable virus polyhedra (PIB) were isolated from external surfaces of parasitic wasps and faeces of tachinid flies, coccinellid larvae, and scavenging flies. Faeces of the scavenging flies remained infectious 9 months on foliage in the field. A bird fed on earthworms from contaminated soil passed infectious faeces. Raindrops on foliage below diseased larval colonies contained more than 10⁸ PIB/ml. It was concluded that although there are numerous transmission pathways, only a few may be available at any one time. The stochastic nature of many pathways implies that the overall transmission rate is highly variable. These results are consistent with frequent observations of low transmission levels between larvae of the same generation.      

Selection of healthy and nuclear polyhedrosis virus infectedAnticarsia gemmatalis [Lep.: Noctuidae] as prey by nymphalNabis roseipennis [Hemiptera: Nabidae] in laboratory and on soybean

Nabis roseipennis Reuter nymphs demonstrated a preference for nuclear polyhedrosis virus (NPV) — infected over healthyAnticarsia gemmatalis Hübner larvae when offered a choice of larval prey in Petri dishes and on soybean. In Petri dishes, small (second-third instar) and large (fifth-sixth instar) nymphs attacked a significantly greater number of diseased than healthy larvae at all larval instars tested (first-fifth instars) and exposure periods (2, 5 and 24 h), except that at 2 h the number of 1^st and 3^rd instar larvae attacked by large nymphs did not differ significantly (P≤0.05). Nabis roseipennis caged with larvae on individual soybean plants in the greenhouse resulted in a generally low percentage of attack by small and large nymphs after 2 days, ranging from 5.6 to 36.7%. As in the Petri dishes, the nabids showed a significant preference for diseased larvae over healthy larvae attacked for all nabid and larval sizes on soybean, with the percentage of diseased larvae attacked ranging from 28.0 to 65.4% (P≤0.05). This preference for diseased larvae on soybean as well as in Petri dishes demonstrates that the preference was not due to the close proximity in which the host and prey were found in the Petri dishes. The preference for diseased larvae may be due to a reduction in a defensive response in late stages of disease. This material is based upon work supported in part by USDA Grant No. 83-CRCR-1-1212.     

Predators as potential dispersal agents of the nuclear polyhedrosis virus ofAnticarsia gemmatalis [Lep.: Noctuidae] in soybean

The relationships were surveyed among an introduced nuclear polyhedrosis virus (AgNPV), populations of its larval hostAnticarsia gemmatalis, and other invertebrates associated with soybean. Early applications of AgNPV to small plots effectively suppressedA. gemmatalis populations without causing detectable perturbations in populations of other phytophagous insects or invertebrate predators. Bioassays of predators collected within and outside treated areas demonstrated that many invertebrates readily fed upon AgNPV-infectedA. gemmatalis under field conditions. These results suggest that the predator complex enhances the epidemic potential of this baculovirus. The predators, by feeding upon virus infected larvae, are believed to play an important role in maintaining and disseminating virus inoculum in soybean. Florida Agricultural Experiment Station Journal Series No. 6272.     

Selection of nuclear polyhedrosis viruses as biological control agents ofSpodoptera exigua [Lep.: Noctuidae]

The virulence of 5 nuclear polyhedrosis viruses infectious for larvae of beet armyworm,Spodoptera exigua, was studied and their potential as biological control agents of this accidentally introduced pest in Dutch greenhouse crops is discussed. Three of the virus isolates were collected from deceased beet armyworm larvae found in Dutch greenhouses. Based on restriction endonuclease patterns of their DNA they appeared to be closely related toMamestra brassicae nuclear polyhedrosis virus (MbMNPV) and therefore were named MbMNPV-NL80, MbMNPV-NL82 and MbMNPV-NL83. These isolates were not related toAutographa californica MNPV (AcMNPV) or toSpodoptera exigua MNPV (SeMNPV), both originating from the USA. Comparison of the oiological activity of these 5 isolates showed that the SeMNPV was more virulent against beet armyworm than the other isolates. There was no significant difference in virulence between MbMNPV-NL80, NL82, NL83 and AcMNPV forS. exigua. The LD-50 values of the 5 isolates for 2nd instar larvae were 3, 26, 14, 17 and 18 polyhedra, respectively. Despite compensating qualities of the other MNPVs, such as a broader host range and potential production in alternate hosts or cell-lines, SeMNPV is considered to be the most suitable candidate as biological control agent of beet armyworm.      

Secondary transmission of a nuclear polyhedrosis virus ofNeodiprion taedae linearis [Hym.: Diprionidae] between larval colonies on loblolly pine

Transmission of a nuclear polyhedrosis virus (NtNPV) of the loblolly pine sawfly,Neodiprion taedae linearis Ross was examined in larval populations on loblolly pine. NtNPV infection of larvae in one colony resulted in transmission to other colonies in the tree. Mortality in untreated colonies was highest when the treated and untreated colonies were located in the upper canopy and when small larvae were treated with virus (42.6–61.9%). Levels of mortality from NtNPV in the untreated colonies were low (2.8–25.0%) when the treated colony was located low in the canopy. Larvae from untreated colonies in the tree were usually large at death. Mortality in untreated larval colonies collected from nearby trees was much less (0.0–27.7%) than that in the trees containing the treated colony. Published with the approval of the Director, Arkansas Agricultural Experiment Station. Use of a trade name does not imply endorsement or guarantee of the product or the exclusion of other products of similar nature.     

Age-related cannibalism and horizontal transmission of a nuclear polyhedrosis virus in larval Spodoptera frugiperda

1. Experiments were carried out to investigate the incidence of cannibalism throughout the larval development of the noctuid moth Spodoptera frugiperda, and to examine the risk of infection from consuming conspecifics infected with a nuclear polyhedrosis virus (SfNPV). 2. Cannibalism was observed commonly even when food was not limiting, but occurred more frequently at low food quantities and/or high rearing densities. The sex of the larvae had no effect on the incidence of cannibalistic behaviour, however the probability of cannibalism occurring was affected by larval stage. The frequency of cannibalism was significantly higher among fifth- and sixth-instar larvae than among earlier instars, and larvae were more likely to consume younger conspecifics than larvae of the same stage. 3. Fifth-instar larvae offered fourth-instar victims fed equally on healthy larvae, virus-infected larvae (2 days post-infection), uninfected corpses, and virus-killed corpses (6 days post-infection). Horizontal transmission of SfNPV was only recorded in larvae offered virus-killed corpses, however, and total mortality in this treatment was only 32%. 4. In a similar experiment, fourth-instar larvae avoided cannibalising virus-killed corpses. Horizontal transmission of SfNPV was recorded in fourth-instar larvae that consumed 2-day post-infected larvae. The low incidence of cannibalism observed in fourth-instar larvae, however, suggests that this is unlikely to provide an important route for the transmission of SfNPV.     

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.     

自同安钮夜蛾幼虫分离的一种核型多角体病毒

对在林间导致同安钮夜蛾Anua indiscriminate Moore幼虫死亡的一种病原物进行了分离和鉴定,并对该病原物进行了室内毒力测定。结果表明：该病原物为核型多角体病毒, 定名为同安钮夜蛾核型多角体病毒(AiNPV)。其对同安钮夜蛾幼虫的致死浓度LC₅₀和LC₉₀分别为3.4×10⁴和3.8×10⁷ PIB/mL。     

A high incidence of parasitism ofHeliothis SPP. [Lep.: Noctuidae] larvae in cotton in Southeastern Arkansas

During 1981 and 1982, bollworm,Heliothis zea (Boddie), and tobacco budworm,H. virescens (F.), larvae (n=3,666) were collected from 41 cotton fields near Portland, Arkansas (USA) to assess the occurrence of parasitism. Three strategies were employed to controlHeliothis spp. in these fields: (1) release ofTrichogramma pretiosum Riley; (2) insecticidal control; or (3) inaction (check). Insecticide use in nonchemical control fields was reduced, but not eliminated.Heliothis spp. larvae collected in cotton had higher parasitism rates in 1981 (30.9%) and 1982 (50.1%) than had been reported for cotton since the advent of organochlorine insecticide usage. Four species of larval parasites and 1 species of larval-pupal parasite were recorded. The larval parasiteMicroplitis croceipes (Cresson) comprised 90.6% and 94.5% of all parasitic insects reared from field collectedHeliothis spp. in 1981 and 1982, respectively. No difference (P>0.05) in level of parasitism existed betweenH. zea andH. virescens. Differences between treatments occurred only in 1982 whenH. zea larvae were parasitized at a greater (P<0.05) rate in check fields (68.3%) than in insecticidal control fields (44.3%). Higher levels of larval parasitism in cotton fields may be a consequence of reduced insecticide usage and changes in materials applied, particularly the pyrethroids. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Dept. of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Transmission of nuclear polyhedrosis virus in laboratory population of the armyworm, Mythimna (Pseudaletia) separata

Armyworm, Mythimna (Pseudaletia) separata, a serious pest of 12 agricultural crops, was artificially infected with its nuclear polyhedrosis virus to study the modes of virus transmission among the laboratory population. Virus transmitted by transovum and transovarial modes passed through polyhedra-fed moths to their progeny.     

Serial passage of Heliothis zea singly embedded nuclear polyhedrosis virus in a homologous cell line

This paper describes the replication and serial passage of Heliothis zea nuclear polyhedrosis virus (NPV) in a H. zea cell line. It was demonstrated that long-term serial passages of the H. zea NPV in homologous host cell culture decreased both the total number of polyhedral inclusion bodies (PIBs) produced and the infectivity of the supernatant as measured by TCID₅₀. The growth curve indicated that infectious material was released from cells 24 hr postinfection (p.i.) and approached a maximal titer 3 days p.i. The kinetics of H. zea NPV decay at 4°, 27°, and 37°C were determined. Infectivity was not detected after 3 weeks at 37°C, but approximately 10^3.5 TCID₅₀/ml activity was still present after 3 and 8 weeks storage at 27° and 4°C, respectively. Electron microscopy confirmed the presence of single embedded virions in the inoculated cells.     

Relative susceptibility of several noctuid species to a nuclear polyhedrosis virus from Heliothis armiger

Several alternate hosts were tested for their relative susceptibility to an isolate of Galleria mellonella nuclear polyhedrosis virus. Neonate Trichoplusia ni, Heliothis zea, and Manduca sexta were all susceptible to per oral administration of purified polyhedra. Of the three alternate species tested, T. ni was the most susceptible, and exhibited the most variable mortality response over the dose range tested, while M. sexta was the least susceptible. We believe this represents the first report of a lethal virus infection in a sphingid species, and useful parameters for the successful inoculation of alternate hosts are discussed.     

Comparison of wild type and genetically engineered nuclear polyhedrosis viruses of Autographa californica for mortality, virus replication and polyhedra production in Trichoplusia ni larvae

Virus replication and polyhedra production of two polyhedron-positive recombinant nuclear polyhedrosis viruses of Autographa californica, AcJHE.KK and AcAaIT which encode juvenile hormone esterase and scorpion toxin, respectively, were compared with those of a plaque purified wild-type nuclear polyhedrosis virus, AcMNPV-C6, in Trichoplusia ni larvae. Though average times required to kill the T. ni larvae increased with the age of the larvae, killing time by either recombinant virus was significantly shorter than that by wild-type virus. Killing time was reduced ca. 30% for AcAaIT-infected larvae and 5 to 8% for AcJHE.KK-infected larvae as compared to that for AcMNPV-C6-infected larvae. The average weight of larvae infected with AcAaIT was significantly lower than that of larvae infected with AcJHE.KK and AcMNPV-C6. The mean numbers of polyhedra produced in each larva inoculated with AcAaIT and AcJHE.KK were ca. 20% and 60%, respectively, of those for AcMNPV-C6. Total virus titers in AcMNPV-C6-infected larvae were significantly higher than those in AcJHE.KK- and AcAaIT-infected larvae until 2 days post infection.     

Functional response ofChrysopa carnea [Neur: Chrysopidae] larvae feeding onHeliothis virescens [Lep.: Noctuidae] eggs on cotton in field cages

The functional response of 3rd instarChrysopa carnea (Stephens) larvae feeding on 4 densities ofHeliothis virescens (F.) eggs was determined on caged cotton (Gossypium hirsutum L.).C. carnea larvae had a mean search rate of 1.08×10⁻⁵ ha/predator-day or 0.11 row-m/predator-day.      

Dispersal of the nuclear polyhedrosis virus of Neodiprion sertifer from soil to pine foliage with dust

Inclusion bodies (PIB) of nuclear polyhedrosis viruses (NPV) remain infectious for long periods in forest soils, but their transfer from soil to foliage is not well understood. Two instances of dispersal of the NPV of Neodiprion sertifer (Fourcroy) (Hymenoptera: Diprionidae) by dust are reported. The distributioo of diseased larval colonies in a young Scots pine stand indicated that dust caused by logging during winter could have started an epizootic. At another site there was a higher frequency of infected colonies near a forest road than further into the stand. The dust transmission hypothesis was tested by bioassays of road surface material and of samples of airborne dust collected on membrane filters. Both soil and air samples contained viable PIBs. Thus, virus dispersal with dust provided a likely explanation for the observed distributions of diseased larval colonies.

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Zusammenfassung Mortalität von N.sertifer Larven durch das wirtsspezifische Kernpolyedervirus ist zwischen den Massenvermehrungen der Sägewespe selten. Eine ständige Infektionskette bleibt nicht erhalten. Das einzige bekannte Reservoir von Virusinoculum zwischen den Massenvermehrungen ist der Waldboden. Die Übertragung von Virus vom Boden auf Kiefernnadeln wird als seltenes Ereignis betrachtet. Sie dürfte häufiger sein, wenn die bodenbedeckende Vegetation gestört ist. Es wird von zwei Studien berichtet, in denen offenbar NPV in windverfrachtetem Staub die Krankheit bei Larven verursachte.In einem jungen Bestand schottischer Kiefer, in dem keine neueren Meldungen von Virusauftreten vorlagen, wurden Proben genommen. Die Proben stammten aus verschiedenen Distanzen von einem ausgewachsenen, im vorherigen Winter gefällten Bestand. Die Befallsintensität sank hier scharf ab mit zunehmender Distanz vom Rand.Ferner wurde der Krankheitsbefall in Larvenkolonien an kleinen Bäumen nahe einer schmalen Forst-strasse und an Bäumen im Bestandesinnern untersucht: In Strassennähe war der Befall höher. Luftmuster wurden nahe der Strasse durch Membranfiltern gesaugt und in einem Biotest auf Virus untersucht. Wenn die Strassenoberfläche ungestört war, wurde kein Virus festgestellt. Wurde Staub aufgewirbelt, konnten infektiöse PIBs gefunden werden. Material von der Strassenoberfläche hatte eine hohe Virusaktivität.Die Übertragung des Virus vom Boden auf Kiefernnadeln dürfte demnach wichtig sein, um Krankheitsausbrüche auszulösen. Die beschriebenen Störungen waren vom Menschen verursacht. Ähnliches könnte sich unter andern Umständen ereignen, z.B. bei Windfall oder bei der Aktivität grösserer Tiere.

     

Characterization and culture of virus replicating continuous insect cell lines from the bollworm,Heliothis zea (boddie)

Summary A series of five discrete virus replicating insect cell lines were isolated from the ovarian and fat body tissues ofHeliothis zea pupae. Two of these cell lines (IPLB-HZ-1075 and-HZ-1079) were studied in depth as to their growth and virus replication responses to specific nutrients (acetyl-β-methylcholine, fresh glutamine) in a number of media. The same two cell lines were identified to species by serological (microimmunodiffusion) and isozyme (phosphoglucoisomerase and peptidase:glycyl-leucine) techniques. Distinguishing comparisons were made with other cell lines that have been confused with the present lines in the literature and with cell line and host pupal extracts from the same and other lepidopteran species studied concurrently in this laboratory. Sterility culture tests were negative for mycoplasmas. The present fiveH. zea lines were the first insect cell lines to replicate polyhedra from a unicapsid multiple embedded nuclear polyhedrosis virus (Baculovirus Group A), in this case the homologous virus obtained from larvae ofH. zea.