Hemolymph factor in armyworm larvae infected with a nuclear-polyhedrosis virus toxic to Apanteles militaris

The parasitoid, Apanteles militaris, was killed or failed to pupate when its armyworm host was infected with the hypertrophic strain of a nuclear-polyhedrosis virus. Virion-free plasma from diseased larvae killed the parasitoids when injected into uninfected larvae. The toxic factor was partially precipitated from plasma that was 50% saturated with ammonium sulfate and was completely precipitated in 50% ethanol or methanol. Parasitoids in larvae infected with the typical strain of nuclear-polyhedrosis virus seemed unaffected.     

Transmission of a baculovirus in populations of Oryctes rhinoceros

The transmission of the baculovirus of Oryctes rhinoceros, previously called Rhabdionvirus oryctes, was studied. O. rhinoceros adults became infected with the virus when kept in a mixture of sawdust and ground-up virus-killed larvae or together with other virus-infected adults. In the field, mated females were more frequently infected than unmated females. Adults developing from larvae that had survived exposure to various dosages of the virus were not infected. No virus infections occurred in larvae hatching from eggs surface-contaminated with the virus. Larvae hatching from eggs laid by virus-infected females very rarely were infected.In the O. rhinoceros population the virus is transmitted most frequently during mating, possibly when the uninfected partner contacts virus material excreted by the infected partner. The virus can be transmitted in a similar way when infected and healthy beetles feed together in palm trees. Beetles visiting larval breeding sites containing freshly virus-killed larvae can become infected. Virus-infected beetles can pass the infection to healthy larvae when visiting a breeding site.     

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.     

Previous herbivore attack of red alder may improve food quality for fall webworm larvae

Summary Three hypotheses of insect-plant interactions were tested by rearing fall webworm larvae in the laboratory on foliage from red alder trees with different histories of western tent caterpillar herbivory. Fall webworm larvae raised on foliage from trees which had been attacked previously for two summers by moderate densities of western tent caterpillars grew faster and attained heavier pupal weights than did those fed foliage from unattacked trees. This contradicts the hypothesis that moderate levels of previous herbivory induces the production of plant defensive chemicals in red alders. Growth of webworms, when fed foliage from unattacked trees adjacent to alders that were attacked by fall webworm larvae, was the same as when fed foliage from trees isolated by distance from attacked trees. This contradicts the hypothesis that attacked trees stimulate the production of defensive chemicals in neigh-boring trees. Young and mature alder foliage was equally good for fall webworm growth and survival, and foliage from trees heavily attacked by both fall webworm and western tent caterpillars for three years produced slow growth rates and small pupal sizes. This supports the hypothesis that continued heavy insect attack can cause the deterioration of the food quality of attacked trees.     

重大外来入侵害虫——美国白蛾生物防治技术研究

美国白蛾Hyphantria cunea(Drury)是重大外来入侵害虫,对我国林业和园林绿化造成重大危害,尤其是近年来美国白蛾传入北京,严重威胁着我国“绿色奥运”的顺利举办和首都园林绿化及生态环境安全。根据美国白蛾多发生在居民区、乡镇和城市的特点,作者开展对环境安全的生物防治技术研究。汲取前苏联等国家从美国白蛾的原产地引进天敌进行生物防治没有成功的经验和教训,立足调查和寻找我国本土天敌。经过21年的努力,发现和筛选出白蛾周氏啮小蜂Chouioia cunea Yang(新属新种)这种寄生美国白蛾的特优天敌;研究这种小蜂的行为学、生态学、生物学、解剖学及人工大量繁殖、放蜂防治技术;筛选出人工大量繁殖小蜂的替代寄主,解决小蜂的大量繁殖的瓶颈问题;通过放蜂防治试验,取得良好的防治效果。同时,筛选出防治美国白蛾的高毒力HcNPV病毒毒株,研制出美国白蛾人工饲料,利用人工饲料大量饲养美国白蛾幼虫,然后接种扩增病毒,成功解决HcNPV病毒大量扩增生产和常年生产的技术难题,做到病毒的规模化生产和常年生产,保证大面积生产防治的需要和病毒质量。研究出利用天敌昆虫和病原微生物综合应用的防治模式:在美国白蛾幼虫期喷洒HcNPV病毒,蛹期释放白蛾周氏啮小蜂,达到既控制当代美国白蛾的危害,又有效抑制其下代的种群数量,取得长期的持续控制美国白蛾的防治效果。上海市、大连市、烟台市和青岛市利用该项技术已经完全控制美国白蛾,特别是上海市利用本项生物防治技术防治后,已经连续6年没有再发现美国白蛾。由于该项生物防治技术利用的是自然界原有的控制害虫的生态因子,因而对环境安全,做到既消灭害虫,又保证生态环境和人畜的安全,也保护生物多样性。该项研究成果也为北京采用“绿色”防治技术有效控制美国白蛾提供重要的科技支撑和技术保障。     

Interinstar susceptibility of the fall webworm,Hyphantria cunea,to its nucleopolyhedrosis and granulosis viruses

Comparative interinstar susceptibility of the fall webworm, Hyphantria cunea, to granulosis and nucleopolyhedrosis viruses was quantitated. As the larvae matured, susceptibility to either baculovirus preparation decreased. Mortality data converted to a dose per milligram body weight basis demonstrated that this decrease in susceptibility was only in part due to the difference in weight of the larvae tested. Lethal time data showed that incubation time for either baculovirus was dependent on the age of the larvae and the dose of virus assayed. A difference in interinstar susceptibility was observed between the granulosis virus and nucleopolyhedrosis virus.     

Effects of 4‐hexylresorcinol on the phenoloxidase from Hyphantria cunea (Lepidoptera: Arctiidae): In vivo and in vitro studies

Insecticidal effects of 4‐hexylresorcinol, a phenoloxidase (PO) inhibitor, were determined on Hyphantria cunea (Drury) under laboratory conditions. The LC₅₀ for the 15‐d‐old larvae was estimated to be 2.95 g/L after 96 h exposure. The activities of glutathione S‐transferase (GST) and PO showed a decrease in larvae treated with 4‐hexylresorcinol, and the IC₅₀ of GST and PO were estimated to be 0.8 and 0.43 g/L, respectively, 24 h after treatment. The PO from the hemolymph of fall webworm was purified by ammonium sulfate precipitation, gel‐filtration, and ion‐exchange chromatography, and then enzymatic characteristics and the mechanism of inhibition were determined using L‐dihydroxyphenylalanine (L‐DOPA) as the substrate. The purified PO showed a single band on SDS‐PAGE with a molecular weight of about 70 kDa. The optimum pH for PO activity was observed at pH 7.0, optimum temperature was found to be 45 °C, and PO activity was strongly inhibited by Zn²⁺. IC₅₀ values were estimated to be 8.2, 19.14, and 24.04 μmol/L for 4‐hexylresorsinol, kojic acid, and quercetin, respectively. The inhibitory potencies (i.e., I₅₀ of each compound/I₅₀ of 4‐hexylresorcinol) of kojic acid and quercetin on H. cunea PO were estimated to be 1.87 and 2.89, respectively. 4‐hexylresorcinol was determined to be a competitive inhibitor, and kojic acid and quercetin were determined to be mixed inhibitors. PO is one of the most important enzymes in an insect's immune system, and the use of PO inhibitors seems to be a promising approach for pest control due to their potential safety for humans.     

A laboratory evaluation of the pathogenicity of Bacillus popilliae var. rhopaea, the agent of milky disease in Rhopaea verreauxi (Coleoptera: Scarabaeidae)

Two methods of infection, i.e., feeding known numbers of spores and rearing larvae in contaminated peat, were used to bioassay the susceptibility of Rhopaea verreauxi to Bacillus popilliae var. rhopaea at 23°C. The susceptibility of the three larval instars was similar as measured by the ID₅₀ and IC₅₀ values. However, within an instar, newly molted larvae were less susceptible than mature larvae when infected by the contaminated peat method. It is suggested that this was due to reduced food intake. The range of ID₅₀ values for all bioassays with R. verreauxi larvae were 1.1 × 10⁷ to 4.0 × 10⁷ spores per larva, and IC₅₀ values were 3.4 × 10⁶ to 5.0 × 10⁷ spores per g of contaminated peat. The slope of the probit line was always low (0.6 to 1.8) except for young first-instar larvae infected by contaminated peat when the slope was 4.0. Disease per se did not affect food intake, though intake was reduced at high doses of contaminated peat. Young larvae often died without developing symptoms but, with increasing age, infected larvae were more likely to develop symptoms. Bioassays with Othnonius batesi and Rhopaea morbillosa indicated a much lower susceptibility per os than for R. verreauxi. It is concluded that the potential for using B. popilliae var. rhopaea to control R. verreauxi is high, but the bacillus is unlikely to be of value in control of O. batesi or R. morbillosa.     

Persistence of insect viruses in field populations of alfalfa insects

The persistence of viruses of five insects was observed in alfalfa fields. The insects were Autographa californica, Colias eurytheme, Pseudaletia unipuncta, Spodoptera exigua, and Trichoplusia ni. The isolated viruses were the granulosis (GV), the cytoplasmic-polyhedrosis (CPV), and the nuclear-polyhedrosis (NPV) viruses. The viruses persisted in the soil, on the alfalfa foliage, and in alternate hosts. In the soil, the viruses persisted even during the winter months when no foliage remained on the plants. Alfalfa sprouts harboring virus-infected larvae of C. eurytheme and S. exigua produced virus infections in larvae of these insects, but those with larvae of A. californica and P. unipuncta did not cause virus infection. The GVs and CPVs isolated from these insects were transmitted to nearly all of the other four species, but the NPVs appeared to be host specific.     

Effects of chlorantraniliprole and chromafenozide on mortality and feeding cessation of the fall webworm,Hyphantria cunea (Lepidoptera: Arctiidae)

The fall webworm (FWW) Hyphantria cunea, native to North America, is a globally invasive pest of a wide range of forest and fruit trees. Spraying of pesticides is the primary method for the control of FWW. In this study, toxicity and feeding cessation of two potential pesticides against the FWW, chlorantraniliprole, and chromafenozide, were evaluated. Both pesticides were slow to affect FWW. For chlorantraniliprole, the highest mortality of third instar larvae occurred at 72 h with an LC₅₀ of 10.34 mg/L, while for chromafenozide, the highest mortality occurred at 72 h with an LC₅₀ value 74.0950 mg/L. Low concentrations of both pesticides led to larvae ceasing to feed after six hours (chlorantraniliprole) and 24 h (chromafenozide). Both pesticides had persistent effects; thirty days after being applied at concentrations of 16, 26.67, and 35.56 mg/L to leaves, 93.33% of newly contacted larvae died after seven days. Our study showed that chlorantraniliprole and chromafenozide could be alternatively used against FWW and form a component of integrated control programs. The results provide information to guide the usage of chlorantraniliprole and chromafenozide in FWW control.     

L'applicazione di un virus poliedrico nucleare nella lotta control larve diLymantria dispar L.

Summary Small scale field tests with a nuclear-polyhedrosis virus were conducted, for the first time in Sardinia during 1965–1966, on the larvae of the gypsy moth (Lymantria dispar L.). Promising results were obtained by spraying the pathogen at several dosage levels on the cork-oak trees (Quercus suber L.). Mortality varied with the concentration of virus used and with the age of the larvae at the time of spraying. In 1965 a suspension containing 1,2×10⁹ purified polyhedra per milliliter gave 100% mortality of the second-instar larvae in 16 days. Lower polyhedra counts gave mortality ranging between 84 and 99 per cent. In 1966 the treatments with a raw suspension containing 10⁸ polyhedra per milliliter brought about the death, in 20 days, of 100 per cent and 93 per cent respectively of the second- and third-instar larvae. Even lower concentrations caused considerable larval mortality. The lower temperatures occurring in 1966 account for the delay in the appearance of elevated mortality rates. Application of the virus to third-instar larvae carrying microsporidian infections (Nosema lymantriae Weiser) led to an accelerated mortality. On the basis of the frass collected it is obvious that the insects fed poorly on the treated trees as compared to the controls. It is not possible to make direct comparisons of dosages between the 1965 and the 1966 treatments. The different feeding activity, however, of second-instar larvae treated with similar concentrations of purified or unpurified polyhedra suggest that further research is necessary in order to ascertain if the frass reduction obtained using the raw virus suspension is not due to a greater efficacy of the unpurified as compared to the purified virus. Field results indicate that a virus suspension containing 10 million polyhedral inclusion bodies per milliliter of water will prevent excessive defoliation of trees by the larvae.      

The effect of the microsporidan, Nosema algerae, on Anopheles stephensi

A bioassay method was established to examine infectivity differences between different batches of Nosema algerae spores. The IC₅₀ of N. algerae spores produced in one unusual host, Heliothis zea, was the same as for spores from the normal mosquito host, Anopheles stephensi. Soil and sand bottoms caused an approximate 200–400 fold increase in the IC₅₀. Nosematosis had little effect on the survival of larvae and pupae but the adult life span was reduced to the extent that malaria transmission would be doubtful.     

Simulated acid rain reduces the susceptibility of the European pine sawfly (Neodiprion sertifer) to its nuclear polyhedrosis virus

Summary The study dealt with the effect of simulated acid rain (both H₂SO₄ and HNO₃; acidities of pH 4 and pH 3) on the susceptibility of the larvae of Neodiprion sertifer to its nuclear polyhedrosis virus. Scots pines growing in a subarctic area with low ambient pollution levels were irrigated with simulated acid rain during two summers. Neodiprion larvae fed with foliage from the experimental trees were infected with a dilute virus suspension. The acid treatment of host trees had a significant effect on the proportion of virus-treated larvae alive 16 days after the virus application: there were almost no differences between the controls and the pH 4 irrigation group, but on the needles of pH 3-treated trees larval survival was twice as high as with other treatments. The direct spraying of acid water on the needles before they were fed to the larvae did not significantly affect the survival of virus infected larvae. Our results suggest that acid rain may reduce the susceptibility of Neodiprion larvae to virus disease via changes in the quality of pine foliage.     

Pathophysiological influences of the Heterorhabditis bacteriophora complex on fifth-instar larvae of the red humped caterpillar, Schizura concinna: Changes in feeding rate,larval weight,and frass production

At 28.5°C, oral dosages of the invasive juveniles of Heterorhabditis bacteriophora and intrahemocoelic injections of its associated bacterium, Xenorhabdus luminescens, resulted in a decrease in larval feeding rate, larval wet weight, and frass production in its host, the seventh-instar larvae of Schizura concinna.     

Pathology and Properties of the Tetravirus Helicoverpa armigera Stunt Virus

A quantitative study of the pathogenicity of Helicoverpa armigera stunt virus (HaSV) (Tetraviridae) isolates toward larvae of several heliothine species was conducted along with studies on the stability of the virus to a variety of chemical, enzymic, and temperature treatments. Surface contamination bioassays of several HaSV isolates against H. armigera produced 50% effective concentration (EC₅₀) estimates ranging between 568 and 9244 virus particles (vp)/mm². Against mid 1st instar larvae of H. armigera, H. punctigera, and Heliothis punctifera, EC₅₀ estimates for one isolate were 1288, 16,137, and 2667 vp/mm², respectively. The virulence of HaSV infection varied markedly with the age at which larvae were exposed to the virus. Presentation of the virus to the first three instars of H. armigera was accompanied by cessation of feeding, growth retardation, and eventual lethality, whereas no adverse effects were observed when later instars were exposed to the virus, even at very high concentrations. Active HaSV was recovered from frass of larvae exposed to the virus as 1st instars. Household bleach (1% v/v; 0.04% w/v available chlorine, 0.004% w/v NaOH), formaldehyde (1% w/v), and temperatures ≥65°C completely inactivated HaSV in suspension. Treatments with ether, proteinase K (1 mg/ml), H. armigera gut contents, and temperatures between 22 and 55°C partially inactivated virus activity. No observable inactivation was observed after treatment with chloroform, chymotrypsin (1 mg/ml), trypsin (1 mg/ml), or RNase A (1 mg/ml). The virus was stable between pH 2.8 and pH 10.0 with around 60% loss of activity observed at pH 11.4. The pattern of pathogenic effects seen in several other insect species challenged by high concentrations of HaSV indicated that the host range of the virus is limited to species within the lepidopteran family Noctuidae. The apparently restricted host range of HaSV along with a number of other features indicate that this virus has considerable potential for the development of novel control agents for use against heliothine pests.     

Bioassay of a nuclear-polyhedrosis virus and Bacillus thuringiensis against the American bollworm, Heliothis armigera, in Botswana

Heliothis armigera is a serious pest in Botswana. Preparations of a local nuclear-polyhedrosis virus and Bacillus thuringiensis (Biotrol BTB-183) are being considered as treatments for control of this pest. Laboratory bioassays of these two preparations were carried out to provide a firm basis for comparison with past field trials and a standard for future field testing. The LC₅₀ of the virus and LD₅₀ of B. thuringiensis were found to compare favorably with those for similar materials against closely and distantly related lepidopterous pests. The majority of larvae were killed very rapidly by the B. thuringiensis, although some survived up to 14 days before death. The minimum time to mortality for the virus was 4 days. B. thuringiensis lowered the weight of both male and female surviving pupae, whereas the virus had no significant effect on its survivors. Concentrations of the two materials calculated from the LC₉₀ and LD₉₀ were considerably lower than those already found to give some or good control of H. armigera on sorghum. Improved spray coverage and protection of the materials against environmental degradation are required if spraying concentrations are to be reduced and yet remain effective.     

Abundance trumps quality: bi‐trophic performance and parasitism risk fail to explain host use in the fall webworm

Factors including host abundance, quality, and the degree to which hosts provide enemy‐free space (EFS) may drive host plant choice by phytophagous insects. Herbivores may also experience fitness tradeoffs among hosts, promoting polyphagy. The fall webworm Hyphantria cunea is a dietary generalist that feeds on a broad array of trees across its geographic range. Here, we investigate the drivers of host tree use by the fall webworm in Connecticut (CT) and Maryland (MD). Neither caterpillar performance nor EFS was associated with the frequency with which host trees were used, and no tradeoff between host quality and EFS was identified. Vegetation surveys adjacent to host trees showed that at both localities, host use was non‐random with respect to tree species, and that the main predictor of use among suitable host trees was host tree abundance. This suggests that webworms are under selection to reduce search time for oviposition sites. Although we did not detect a tradeoff between host plant quality and availability in MD, we did identify that tradeoff in CT. This disparity amid otherwise similar patterns of host use between CT and MD may be explained by the relative rarity of high quality hosts in CT compared to MD. Our results illustrate that geographic mosaics in patterns of host use may arise in the absence of local adaptation if host use is based upon availability rather than host plant attributes.     

Interactions between a fungal pathogen, foliar properties, and generalist herbivores

American [Castanea dentata (Marsh) Borkh.] × Chinese [Castanea mollissima Blume] chestnut (Fagac, ae) hybrids are a novel system in which to study influences of phytopathogenic fungi and woody plant hybridization on herbivore susceptibility, as the hybrids are well characterized with regard to resistance to the chestnut blight fungus [Cryphonectria parasita (Murr) Barr (Endothia) Diaporthales: Valsaceae] and variability is present. We chose two groups of resistance‐rated backcross chestnut that shared an F1 parent and had different American parents. Foliage from both backcross groups and the parent trees was sampled on three dates for use in feeding assays with gypsy moth larvae [Lymantria dispar (L.) [Lepidoptera: Lymantriidae], adult Japanese beetles [Popillia japonica Newman (Coleoptera: Scarabaeidae)], and fall webworm larvae [Hyphantria cunea Drury (Lepidoptera: Arctiidae)], respectively. Foliar analyses were performed concurrently and included carbohydrate, tannin, and nitrogen content, toughness, and density. Blight resistance had almost no effect on herbivore performance or foliar chemistry. When the parent trees and backcross groups were compared, however, significant differences in gypsy moth performance and Japanese beetle consumption were evident. There were no differences in fall webworm consumption. Most foliar characteristics measured differed among chestnut genotypes at some point in the season, and all varied seasonally. No clear pattern emerges with respect to the relationship among blight resistance, herbivore susceptibility, foliar properties, and plant genotype, and more research is needed to separate these effects.     

Biology ofHyphantria cunea Drury (Lepidoptera: arctiidae) in Japan. V. Preliminary life tables and mortality data in urban areas

Studies on the population dynamics of the fall webworm, Hyphantria cunea have been carried out at three survey stations and along selected roads in the urban area of Tokyo since 1966. Twelve survivorship curves obtained during two years and 8 life tables show that the mortality rate in early developmental stages of the fall webworm is remarkably low as compared with that of other lepidopterous defoliaters and the mortality rate in later developmental stages is compensatory high. The low mortality rate in early stages is considered to be due to the protective role of the nest-web and the lack of egg and larval parasites. All but one parasitic species emerge from prepupae and pupae. Spiders living in the nest-web of the fall webworm play an important role in reducing the number of young larvae. Direct observations and caging experiments showed that relatively high mortality during later larval stages is mainly due to predation by birds (in the first generation) and wasps (in the second generation). The generation mortality in the survey stations always exceeded the level where the population is kept at the steady state, and the outbreak of this moth is considered to be continued by the immigration of adults from large trees growing in gardens on which the larvae can escape from predation pressure.     

The effect of the granulovirus (PapyGV) on larval mortality and feeding behaviour of the Pandemis leafroller,Pandemis pyrusana (Lepidoptera: Tortricidae)

An indigenous betabaculovirus (PapyGV) of the Pandemis leafroller, Pandemis pyrusana (Kearfott), was studied in the laboratory and greenhouse to determine how the virus affected leafroller mortality and foliar damage. Probability of mortality increased with virus concentration as observed after 7 and 10 days of feeding on virus treated diet in neonates and second instar larvae. LC₅₀ estimates for neonates at 7 and 10 days was 2743 and 389 occlusion bodies (OBs)/mm². For second instars, LC₅₀ was 139,487 and 813 OBs/mm² at 7 and 10 days. There was no biologically significant mortality response to increasing virus concentrations by fourth instar larvae; however, when fourth instar larvae were infected with virus on diet and then fed apple leaves, the leaf area consumed declined up to 50% with higher virus concentrations. In a greenhouse study, neonate larvae that fed on seedlings treated with water showed >90% survival and 80% pupation rate of larvae after being transferred to diet. In contrast, larvae that fed on apple seedlings sprayed with 3×10⁶ OBs/ml showed poor survival when transferred to diet after acquiring the virus and failed to reach the pupal stage. This virus shows promise for population regulation and can produce reduction in feeding damage.