Increased mortality of gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae) exposed to gypsy moth nuclear polyhedrosis virus in combination with the phenolic gycoside salicin

Second instar gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), larvae suffered significantly greater mortality from aerially applied gypsy moth nuclear polyhedrosis virus (Gypchek) when the virus was consumed on quaking aspen, Populus tremuloides Michx., versus red oak, Quercus spp. L., foliage. Laboratory assays in which various doses of Gypchek and salicin (a phenolic glycoside present in aspen foliage) were tested in combination demonstrated that salicin significantly increased total larval mortality and lowered the LD50 estimates (dose of Gypchek that resulted in 50% population mortality) for the virus, although not significantly. While salicin did not impact larval survival in the absence of Gypcek, it did act to significantly deter feeding when it was present in high concentrations (up to 5.0%) within the treatment formulations. The enhanced activity of Gypchek in the presence of salicin is similar to prior reports of enhanced activity of the bacterial pathogen Bacillus thuringiensis when consumed concurrently with phenolic glycosides commonly present in aspen foliage. The enhancement of viral activity is in contrast to the inhibitory effects on the virus reported for another common group of phenolic compounds, tannins.     

Competition between the gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis: interactions mediated by host plant chemistry, pathogens, and parasitoids

The gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis, overlap geographically as well as in their host ranges. Adult female swallowtails are incapable of distinguishing between damaged and undamaged leaves, and the opportunities for competition between these two species are numerous. We designed field and laboratory experiments to look for evidence of indirect competition between P. canadensis and L. dispar larvae. Swallowtail caterpillars were reared in the laboratory on leaves from gypsy-moth-defoliated and undefoliated trees to explore host-plant effects. We tested for pathogen-mediated interactions by rearing swallowtail larvae on both sterilized and unsterilized leaves from defoliated and undefoliated sources. In addition, we measured the effects of known gypsy moth pathogens, as well as gypsy moth body fluids, on the growth and survival of swallowtail larvae. Field experiments were designed to detect the presence of parasitoid-mediated competition, as well: we recorded parasitism of swallowtail caterpillars placed in the field either where there were no gypsy moth larvae present, or where we had artificially created dense gypsy moth populations. We found evidence that swallowtails were negatively affected by gypsy moths in several ways: defoliation by gypsy moths depressed swallowtail growth rate and survival, whether leaves were sterilized or not; sterilization significantly reduced the effect of defoliation, and gypsy moth body fluids proved lethal; and swallowtail caterpillars suffered significantly increased rates of parasitism when they were placed in the field near gypsy moth infestations.     

Effect of two granulosis viruses on the activity of the gypsy moth (Lepidoptera: Lymantriidae) nuclear polyhedrosis virus

Two granulosis viruses (GV) were tested as enhancers for the gypsy moth nuclear polyhedrosis virus (LdMNPV). Helicoverpa armigera (Hübner) CV (HaGV) had no detrimental effect upon larval growth and development, but in combination with LdMNPV it reduced both the LC50 and the LT50 for the NPV. In addition, the combination also adversely affected the growth and development of gypsy moth larvae. The LC50 of LdMNPV was reduced by as much as 300-fold (HaGV at 10(-2) dilution) and the LT50 was reduced by as much as 18% (HaGV at 10(-2) dilution). Spodoptera frugiperda (J. E. Smith) GV reduced the LC50 of LdMNPV by as much as 13-fold but had no effect upon the LT50.     

A field release of genetically engineered gypsy moth (Lymantria dispar L.) nuclear polyhedrosis virus (LdNPV)

The gypsy moth (Lymantria dispar L.) nuclear polyhedrosis virus was genetically engineered for nonpersistence by removal of the gene coding for polyhedrin production and stabilized using a coocclusion process. A beta-galactosidase marker gene was inserted into the genetically engineered virus (LdGEV) so that infected larvae could be tested for its presence using a colorimetric assay. In 1993, LdGEV-infected gypsy moths were released in a forested plot in Massachusetts to test for spread and persistence. A similar forested plot 2 km away served as a control. For 3 years (1993-1995), gypsy moths were established in the two plots in Massachusetts to serve as test and control populations. Each week, larvae were collected from both plots. These field-collected larvae were reared individually, checked for mortality, and then tested for the presence of beta-galactosidase. Other gypsy moth larvae were confined on LdGEV-contaminated foliage for 1 week and then treated as the field-collected larvae. The LdGEV was sought in bark, litter, and soil samples collected from each plot. To verify the presence of the LdGEV, polymerase chain reaction, slot blot DNA hybridization, and restriction enzyme analysis were also used on larval samples. Field-collected larvae infected with the engineered virus were recovered in the release plot in 1993, but not in subsequent years; no field-collected larvae from the control plot contained the engineered virus. Larvae confined on LdGEV-contaminated foliage were killed by the virus. No LdGEV was recovered from bark, litter, or soil samples from either of the plots.     

Induced plant defenses breached? Phytochemical induction protects an herbivore from disease

Although wound-induced responses in plants are widespread, neither the ecological nor the evolutionary significance of phytochemical induction is clear. Several studies have shown, for example, that induced responses can act against both plant pathogens and herbivores simultaneously. We present the first evidence that phytochemical induction can inhibit a pathogen of the herbivore responsible for the defoliation. In 1990, we generated leaf damage by enclosing gypsy moth larvae on branches of red oak trees. We then inoculated a second cohort of larvae with a nuclear polyhedrosis virus (LdNPV) on foliage from the damaged branches. Larvae were less susceptible to virus consumed on foliage from branches with increasing levels of defoliation, and with higher concentrations of gallotannin. Defoliation itself was not related to any of our chemistry measures. Field sampling supported the results of our experiments: death from virus among feral larvae collected from unmanipulated trees was also negatively correlated with defoliation. In 1991, defoliation and gallotannin were again found to inhibit the virus. In addition, gallotannin concentrations were found to be positively correlated with defoliation the previous year. Compared with previous results that demonstrated a delecterious effect of induction on gypsy moth pupal weight and fecundity, the inhibition of the virus should confer an advantage to the gypsy moth. Since leaf damage levels increase as gypsy moth density increases, and since leaf damage inhibits the gypsy moth virus, there is the potential for positive feedback in the system. If phytochemical induction in red oak can inhibit an animal pathogen such as LdNPV, it suggests to us that induction in red oak is a generalized response to tissue damage rather than an adaptive defense against herbivores.     

Adult feeding affects fecundity of the predator,Calosoma sycophanta (Col.: Carabidae)

Calosoma sycophanta L. adults were fed either gypsy moth (Lymantria dispar L.) larvae or split grapes for set periods of time while their reproduction was monitored. Few female beetles reproduced unless fed gypsy moth larvae during the first week after they ended hibernation. Even females initially fed grapes that were later fed larvae had reduced reproduction. The implications these results have for relationships between beetle and gypsy moth populations are discussed.     

Effects of nutrient availability on biomass allocation as well as constitutive and rapid induced herbivore resistance in poplar

Many studies have examined effects of nutrient availability on constitutive herbivore resistance of plants, but few have addressed effects on expression of rapid induced resistance (RIR). We quantified effects of two levels of nutrient availability on growth, biomass allocation, photosynthesis, and constitutive secondary metabolism of black poplar (Populus nigra). We also examined effects of nutrient availability on expression of constitutive resistance of poplar to gypsy moth (Lymantria dispar) and whitemarked tussock moth (Orgyia leucostigma), as well as RIR to both folivores in response to localized herbivory by gypsy moth. The high nutrient treatment had no effect on photosynthetic rate of poplar, but dramatically increased relative growth rate, total biomass, and total leaf area, while foliar phenolic concentrations and root:shoot ratio decreased. Plant growth was negatively correlated with foliar phenolic concentrations, which is consistent with predictions of the Growth/Differentiation Balance Hypothesis when increased nutrient availability increases growth without affecting photosynthesis. These responses of root:shoot ratio and constitutive secondary metabolism to nutrient availability are consistent with those proposed by models of adaptive phenotypic plasticity in resource allocation patterns. Nutrient availability affected constitutive resistance of poplar to first and fifth instar gypsy moth larvae, which grew much faster on high fertility plants. However, nutrient availability had no effect on constitutive resistance to whitemarked tussock moth. Localized herbivory elicited systemic RIR in poplar within 72 hours. However, the magnitude of RIR was dependent on nutrient availability, with differing effects on the two insect species. Expression of RIR to gypsy moth was most dramatic in the high fertility treatment. In contrast, RIR to whitemarked tussock moth was expressed only in the low fertility treatment. The idiosyncratic nature of effects of nutrient availability on constitutive and induced resistance challenges the value of using insect bioassays as surrogate measures of secondary metabolism for testing allocation models of plant defense, as well as the value of generalized plant defense models for predicting effects of environmental variation on resistance to specific herbivores. These results also suggest that the effects of nutrient availability on the expression of RIR may represent a largely over‐looked source of variation in plant/herbivore interactions.     

荧光素对舞毒蛾核型多角体病毒不同地理品系的增效与光保护作用

舞毒蛾Lymantria dispar L.是源于欧亚大陆的多食性叶部害虫,取食300多种乔灌木,现已分布于北美、北非,成为世界性危险害虫之一,给林业生产带来了巨大损失。舞毒蛾核型多角体病毒(LdMNPV)是控制舞毒蛾种群动态的重要生物因素,可引起舞毒蛾种群急剧下降。在室内采用青杨枝条饲养的方法,测定了来自中国、北美和日本的3个LdMNPV品系(分别为LdMNPV-H,LdMNPV-D和LdMNPV-J)对危害青杨的亚洲型舞毒蛾幼虫的毒力,并测定了荧光素Tinopal LPW对它们的增效和光保护作用。结果表明Tinopal LPW对LdMNPV 3个地理品系均有增效和光保护作用,而且随着Tinopal LPW浓度的增加,增效作用增强,1%Tinopal LPW的增效作用最好。添加1%Tinopal LPW的LdMNPV-D品系、LdMNPV-H品系和LdMNPV-J品系对取食青杨的舞毒蛾幼虫的致死中浓度(LC50)分别为1.0、1.6、17.6 OBs/μL,不添加1%Tinopal LPW时,它们的LC50分别为32.9、39.0、1076.4 OBs/μL,分别降低了33、24、61倍。不添加1%Tinopal LPW时,D、H和J品系对舞毒蛾二龄幼虫的致LC95分别是2125.5、1275.8、303540.0 OBs/μL,添加1%Tinopal LPW后LC95分别为73.0、285.4、2360.8OBs/μL,分别降低了26、4.5、128.6倍。此外,1%Tinopal LPW的荧光素使3个品系的致死中时间(LT50)分别缩短了2.9d、5.3d、1.2d。LdMNPV-D和LdMNPV-H品系对亚洲型舞毒蛾表现出低致死中浓度、较短的致死中时间和较大的斜率,二者的毒力较LdMNPV-J品系高,在生产实践中应选择LdMNPV-D添加1%Tinopal LPW。Tinopal LPW对LdMNPV-D、LdMNPV-H和LdMNPV-J 3个品系均有光保护作用,添加1%Tinopal LPW后在距离30W紫外灯40cm下照射16h后,它们毒力保持系数比未添加Tinopal LPW分别高1.8、2.6、1.8倍。     

Influence of Diet and Density on Laboratory Cannibalism Behaviors in Gypsy Moth Larvae (Lymantria dispar L.)

The gypsy moth (Lymantria dispar) is an insect folivore that feeds on a broad range of hosts, and undergoes intermittent outbreaks that cause extensive tree mortality. Like many other herbivorous insects, gypsy moth larvae consume a substrate that is low in nitrogen. Gypsy moth larvae have been known to cannibalize under crowded conditions in the laboratory. In this study, we assessed the influence of nitrogen and density on cannibalism behavior in gypsy moth larvae. Cannibalism rates increased with decreased nitrogen and increased density. There was no interaction between these two parameters. Developmental experiments confirmed that low dietary nitrogen is detrimental, in agreement with previous studies. In a second experiment, we assessed the influence of previous cannibalism experiences on subsequent cannibalism behavior. Gypsy moth larvae that had previously cannibalized other larvae subsequently exhibited higher cannibalism rates than those larvae that had not cannibalized. In conclusion, low nitrogen, high larval density, and previous cannibalism experience are important factors contributing to gypsy moth larval cannibalism. Future studies are needed to estimate benefits to larvae, and to more closely approximate field conditions.     

Effect of the Host Plant on the Antioxidative Defence in the Midgut of Lymantria dispar L. Caterpillars of Different Population Origins

THE RESPONSES OF GYPSY MOTH LARVAE ORIGINATING FROM TWO POPULATIONS (OAK FOREST, LOCUST FOREST) TO FAVORABLE (OAK) AND UNFAVORABLE (LOCUST) HOST PLANTS WERE MONITORED AT THE LEVEL OF MIDGUT ANTIOXIDATIVE DEFENCE: the activities of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione reductase (GR), glutathione peroxidase like ('GSH-Px like') and glutathione content (GSH). Short-term change of the diet (3 days) to locust leaves of the 5th instar larvae (oak population) provoked an increase in GST and 'GSH-Px like' activities as well as in the amount of GSH. On the contrary, transferring the gypsy moth larvae (locust population) to oak leaves was followed by a decrease in GST, 'GSH-Px like' activities, and in the amount of GSH. Feeding gypsy moth larvae from hatching on an unfavorable host plant such as locust, led to increases in GST and SOD activities and GSH content, as well as to a decrease in CAT activity in all instars studied (4th, 5th, 6th). The locust leaf diet caused changes in other components of antioxidative defence dependent on larval instar and population origin, a feature which could be ascribed to trophic adaptation of the gypsy moth to an unfavorable host plant.     

Facilitation between invasive herbivores: hemlock woolly adelgid increases gypsy moth preference for and performance on eastern hemlock

1. Interactions between invertebrate herbivores with different feeding modes are common on long-lived woody plants. In cases where one herbivore facilitates the success of another, the consequences for their shared host plant may be severe. Eastern hemlock (Tsuga canadensis), a canopy-dominant conifer native to the eastern U.S., is currently threatened with extirpation by the invasive stylet-feeding hemlock woolly adelgid (Adelges tsugae). The effect of adelgid on invasive hemlock-feeding folivores remains unknown. 2. This study evaluated the impact of feeding by hemlock woolly adelgid on gypsy moth (Lymantria dispar) larval preference for, and performance on, eastern hemlock. To assess preference, 245 field-grown hemlocks were surveyed for gypsy moth herbivory damage and laboratory paired-choice bioassays were conducted. To assess performance, gypsy moth larvae were reared to pupation on adelgid-infested or uninfested hemlock foliage, and pupal weight, proportional weight gain, and larval period were analysed. 3. Adelgid-infested hemlocks experienced more gypsy moth herbivory than did uninfested control trees, and laboratory tests confirmed that gypsy moth larvae preferentially feed on adelgid-infested hemlock foliage. Gypsy moth larvae reared to pupation on adelgid-infested foliage gained more weight than larvae reared on uninfested control foliage. 4. These results suggest that the synergistic effect of adelgid and gypsy moth poses an additional threat to eastern hemlock that may increase extirpation risk and ecological impact throughout most of its range.     

Endogenous and induced monooxygenase activity in gypsy moth larvae feeding on natural and artificial diets

NADPH oxidase activity was measured in third to sixth instar gypsy moth larvae fed oak or pine foliage. Activity levels ranged from 400 to 1,900 pmol NADPH oxidized/min/mg microsomal protein, but enzyme activity was not correlated with host plant ingested. Similarly, activity levels in larvae fed diets containing inducers, such as the terpenoid α-pinene or pentamethylbenzene, ranged from 700 to 1,500 pmol NADPH oxidized/min/mg protein, levels that were comparable to those measured for larvae fed control diets. O-demethylase activity in older instar gypsy moth larvae fed pine averaged 109 pmol p-nitrophenol/min/mg protein, and activity levels in those fed diet containing α-pinene ranged from 22 to 55 pmol/min/mg protein. Although statistically significant, these induced O-demethylase levels are well below those observed for Heliothis zea larvae. Our findings indicate that monooxygenases play a minor, if any, role in the ability of later instar gypsy moth larvae to develop successfully on pine foliage.     

Effects of elicitation treatment and genotypic variation on induced resistance in Populus: impacts on gypsy moth (Lepidoptera: Lymantriidae) development and feeding behavior

We examined the effects of various wounding treatments and genotypic variation on induced resistance in Populus (Salicales: Salicaceae) against herbivory by the gypsy moth, Lymantria dispar L. (Lepidoptera: Lymantriidae). Second-instar larvae grew and consumed less on leaves from induced than non-induced trees. Likewise, larvae preferred leaf disks from non-induced trees. Among induction treatments, gypsy moth feeding had the strongest and most consistent effect in behavioral choice tests. Mechanical wounding of leaves and mechanical wounding plus application of gypsy moth regurgitant had intermediate effects, while application of jasmonic acid had the weakest overall effect. Under no-choice conditions, there were no consistent trends across clones in the ability of various treatments to elicit plant responses affecting the herbivore. Levels of constitutive and inducible resistance to herbivory varied significantly among 12 Populus clones. Larvae grew up to 30-fold more, and consumed up to 250-fold more on the most suitable than the least suitable clone. Prior feeding by gypsy moths reduced larval feeding up to 71.4% on the most highly inducible clone, but it had little or no effect for the least inducible clones. There was no evidence for a relationship between levels of inducible and constitutive resistance, or between inducible resistance and phylogenetic relatedness among clones. We discuss implications for the ecology and evolution of plant-insect interactions and the management of insect pests. Received: 12 October 1998 / Accepted: 22 March 1999     

Gypsy moth (Lymantria dispar) larval development and survival to pupation on diet plus extractables from green ash foliage

Gypsy moth, Lymantria dispar L., rate of larval development, molting, pupal weight and survival were studied on an artificial diet containing different concentrations of green ash ethyl acetate extractables (EtOAc Exts). Insects were reared on experimental diets from egg to pupa. Addition of EtOAc Exts to artificial diet significantly prolonged larval development and reduced their survival compared to larvae reared on control diet. Weights of pupae were significantly reduced when larvae were reared on diet containing the lowest dosage of EtOAc Exts (i.e., 0.01%) versus on control diet. EtOAc Exts in diet (e.g., 0.01, 0.06 and 0.2%) frequently caused incomplete ecdysis which invariably resulted in larval death. Impaired feeding, locomotion and excretion are likely causes of death. The combination of these results with our earlier findings of repellents and feeding deterrents against gypsy moth larvae (GML) in green ash foliage shows that the non-host status of green ash to the highly polyphagous GML involves three orders of chemical defense: repellents, feeding deterrents and inhibitors of nutritional and developmental physiology. As the insect becomes sequentially exposed to these orders of defense, it incurs higher costs because the adverse effects become less reversible.     

Location of a lepidopteran specificity region in insecticidal crystal protein CryllA from Bacillus thuringiensis

The Bacilius thuringiensis insecticidal crystal protein CryllA has both high mosquito activity and gypsy moth activity; in contrast CryllB, which is 87% homologous, displays no mosquito activity and has a threefold lower gypsy moth activity. The regions responsible for specificity against gypsy moth (Lymantria dispar) and mosquito (Aedes aegypti) larvae were located by introducing Mlul and Xhol sites into homologous positions within the putative domain ii of both cryllA and cryllB genes, which divided almost equally the respective second domains into three regions. Taking advantage of naturally occurring Nhel and Narl sites that border the putative domain II, a set of seven chimeric proteins were produced by exchanging all combinations of those regions Isetween CryllA and CryllB. Analysis of the toxicity of these chimeric proteins demonstrated that the lepidopteran and dipteran specificity regions of CryllA were not collnear. While the specificity region of CryllA against mosquito larvae involved region 1 and probably also region 2, the specificity region of CryllA against gypsy moth larvae was located within region 2.     

Host‐associated divergence in the activity of digestive enzymes in two populations of the gypsy moth Lymantria dispar (Lepidoptera: Erebidae)

The gypsy moth is a generalist insect pest with an extremely wide host range. Adaptive responses of digestive enzymes are important for the successful utilization of plant hosts that differ in the contents and ratios of constituent nutrients and allelochemicals. In the present study, we examined the responses of α‐amylase, trypsin, and leucine aminopeptidase to two tree hosts (suitable oak, Quercus cerris, and unsuitable locust tree, Robinia pseudoacacia) in the fourth, fifth, and sixth instars of gypsy moth larvae originating from oak and locust tree forest populations (hereafter assigned as Quercus and Robinia populations, respectively). Gypsy moths from the Robinia forest had been adapting to this unsuitable host for more than 40 generations. To test for population‐level host plant specialization, we applied a two‐population × two‐host experimental design. We compared the levels, developmental patterns, and plasticities of the activities of enzymes. The locust tree diet increased enzyme activity in the fourth instar and reduced activity in advanced instars of the Quercus larvae in comparison to the oak diet. These larvae also exhibited opposite developmental trajectories on the two hosts, i.e. activity increased on the oak diet and decreased on the locust tree diet with the progress of instar. Larvae of the Robinia population were characterized by reduced plasticity of enzyme activity and its developmental trajectories. In addition, elevated trypsin activity in response to an unsuitable host was observed in all instar larvae of the Robinia population, which demonstrated that Robinia larvae had an improved digestive performance than did Quercus larvae.     

Semipermissive Replication of a Nuclear Polyhedrosis Virus of Autographa californica in a Gypsy Moth Cell Line

Several gypsy moth cell lines have been previously described as nonpermissive for the multiple-embedded nuclear polyhedrosis virus of Autographa californica (AcMNPV). In this report, we demonstrate the semipermissive infection of a gypsy moth cell line, IPLB-LD-652Y, with AcMNPV. IPLB-LD-652Y cells infected with AcMNPV produced classic cytopathic effects but failed to yield infectious progeny virus. Results of experiments employing DNA-DNA dot hybridization suggested that AcMNPV DNA synthesis was initiated from 8 to 12 h postinfection (p.i.), continued at a maximum rate from 12 to 20 h p.i., and declined from 20 to 36 h p.i. The rate of AcMNPV DNA synthesis approximated that observed in the permissive TN-368 cell line. AcMNPV-infected IPLB-LD-652Y cells, pulse-labeled with [(35)S]methionine at various time intervals p.i. and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, revealed four virus-induced proteins, one novel to the semipermissive system and three early alpha proteins, synthesized from 1 to 20 h p.i. Thereafter, both host and viral protein synthesis was completely suppressed. These results suggest that AcMNPV adsorbed, penetrated, and initiated limited macromolecular synthesis in the semipermissive gypsy moth cell line. However, the infection cycle was restricted during the early phase of AcMNPV replication.     

Host heterogeneity in susceptibility and disease dynamics: tests of a mathematical model

Most mathematical models of disease assume that transmission is linearly dependent on the densities of host and pathogen. Recent data for animal diseases, however, have cast doubt on this assumption, without assessing the usefulness of alternative models. In this article, we use a combination of laboratory dose-response experiments, field transmission experiments, and observations of naturally occurring populations to show that virus transmission in gypsy moths is a nonlinear function of virus density, apparently because of heterogeneity among individual gypsy moth larvae in their susceptibility to the virus. Dose-response experiments showed that larvae from a laboratory colony of gypsy moths are substantially less heterogeneous in their susceptibility to the virus than are larvae from feral populations, and field experiments showed that there is a more strongly nonlinear relationship between transmission and virus density for feral larvae than for lab larvae. This nonlinearity in transmission changes the dynamics of the virus in natural populations so that a model incorporating host heterogeneity in susceptibility to the virus gives a much better fit to data on virus dynamics from large-scale field plots than does a classical model that ignores host heterogeneity. Our results suggest that heterogeneity among individuals has important effects on the dynamics of disease in insects at several spatial and temporal scales and that heterogeneity in susceptibility may be of general importance in the ecology of disease.     

Field testing Chinese and Japanese gypsy moth nucleopolyhedrovirus and disparvirus against a Chinese population of Lymantria dispar asiatica in Huhhot, Inner Mongolia, People's Republic of China

The activity of three geographic isolates of the gypsy moth nucleopolyhedrovirus (LdMNPV) was evaluated in field trials against larvae of the Chinese population of Lymantria dispar asiatica Vnukovskij in Inner Mongolia, People's Republic of China, in 2004, 2005, and 2006. Although the Chinese isolate of the virus, LdMNPV-H, was the most pathogenic of the isolates tested, having the lowest mean lethal concentration causing 50% and 95% larval mortality, the increase in efficacy that would be obtained by incorporating this isolate into a commercial product does not justify the time or expense required to register it for use in the United States or Canada. The commercially available North American isolate, LdMNPV-D, was moderately pathogenic, whereas the Japanese isolate, LdMNPV-J, was the least pathogenic. The slopes of the dose-response regression lines for the three virus isolates indicated that the Chinese gypsy moth larvae were more homogenously susceptible to LdMNPV-H and LdMNPV-D than to LdMNPV-J. Time-response data showed that LdMNPV-J was significantly more virulent, but at a much higher dose, than the other two isolates, causing 50% mortality in the shortest time, followed by LdMNPV-H and LdMNPV-D. Rainfall immediately after the application of LdMNPV-D in 2005 resulted in significantly reduced gypsy moth larval mortality.     

Asynchrony between Host Plant and Insects-Defoliator within a Tritrophic System: The Role of Herbivore Innate Immunity

The effects of asynchrony in the phenology of spring-feeding insect-defoliators and their host plants on insects’ fitness, as well as the importance of this effect for the population dynamics of outbreaking species of insects, is a widespread and well-documented phenomenon. However, the spreading of this phenomenon through the food chain, and especially those mechanisms operating this spreading, are still unclear. In this paper, we study the effect of seasonally declined leafquality (estimated in terms of phenolics and nitrogen content) on herbivore fitness, immune parameters and resistance against pathogen by using the silver birch Betula pendula—gypsy moth Lymantria dispar—nucleopolyhedrovirus as the tritrophic system. We show that a phenological mismatch induced by the delay in the emergence of gypsy moth larvae and following feeding on mature leaves has negative effects on the female pupal weight, on the rate of larval development and on the activity of phenoloxidase in the plasma of haemolymph. In addition, the larval susceptibility to exogenous nucleopolyhydrovirus infection as well as covert virus activation were both enhanced due to the phenological mismatch. The observed effects of phenological mismatch on insect-baculovirus interaction may partially explain the strong and fast fluctuations in the population dynamics of the gypsy moth that is often observed in the studied part of the defoliator area. This study also reveals some indirect mechanisms of effect related to host plant quality, which operate through the insect innate immune status and affect resistance to both exogenous and endogenous virus.