Gypsy Moth Nuclear Polyhedrosis Virus Research Articles

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.

POTENTIAL IMPACTS OF BACILLUS THURINGIENSIS VAR. KURSTAKI ON FIVE SALAMANDER SPECIES IN WEST VIRGINIA

Abstract Indirect effects of the microbial pesticide, Bacillus thuringiensis var. kurstaki (B.t.k.), have been found in birds, mammals, and some parasitic insects as a result of reduced abundance of lepidopteran larvae. Salamanders are insectivores that often contain high percentages of lepidopteran larvae in their diets. This study tested the hypothesis that salamanders experience dietary shifts or reduced abundance on plots where B.t.k. is applied, as a function of decreased caterpillar abundance. Three plots in the Monongahela National Forest, Pocahontas County, WV were sprayed with B.t.k., three were sprayed with the gypsy moth nuclear polyhedrosis virus (Gypchek®), and three remained as unsprayed reference sites. Abundance and diet composition of five species of Plethodontidae (Desmognathus fuscus, D. monticola, D. ochrophaeus, Plethodon cinereus, P. glutinosus) were studied for two years. Neither salamander abundance nor the proportions of the major prey items in their diets differed significantly b...

Potentiation by a Granulosis Virus of Gypchek, the Gypsy Moth (Lepidoptera: Lymantriidae) Nuclear Polyhedrosis Virus Product

Gypchek and a granulosis virus were applied in various combinations against several gypsy moth instars under field conditions, and a Blankophor BBH + Gypchek treatment was included as a comparison of virus enhancers. The residual effects of the treatments were determined over a 3-wk period. The addition of Helicoverpa armigera granulosis virus at a 1:100 dilution to Gypchek resulted in an approximate 10-fold increase in observed mortality, while the addition of Blankophor BBH at 1% resulted in an approximate 100-fold increase in observed mortality. The addition of Helicoverpa armigera granulosis virus at a 1:1000 dilution resulted in no consistent increase in recorded mortality, and the 1:100 granulosis virus dilution applied alone was inactive against gypsy moth. The residual activity of Gypchek was little enhanced by the addition of the granulosis virus at either dose.

The Effects of Cations on the Activity of the Gypsy Moth (Lepidoptera: Lymantriidae) Nuclear Polyhedrosis Virus

Fourteen cations were tested at a 1% concentration (wt:wt), as chlorides, for their effects on the biological activity of the gypsy moth, Lymantria dispar (L.), nuclear polyhedrosis virus (LdMNPV). Cupric chloride was toxic to gypsy moth larvae. Ferrous and ferric chloride were inhibitory to larval growth and development as well as to virus activity. Strontium chloride was inhibitory to virus activity but had no apparent effects on gypsy moth larvae. Six cations had little or no effect on virus activity (i.e., calcium, lanthanum, magnesium, nickel, potassium, sodium), whereas four cations (i.e., cobalt, manganese, ruthenium, zinc) acted as viral enhancers, as indicated by reductions in LC50s.

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.

Abundance, Diversity, and Activity of Ants (Hymenoptera: Formicidae) in Oak-Dominated Mixed Appalachian Forests Treated with Microbial Pesticides

This study is part of a long-term analysis of nontarget effects of microbial pesticide application in the George Washington (Augusta County, VA, USA) and Monongahela National Forests (Pocahontas County, WV, USA). Ants were collected using pitfall traps to assess the effect of Bacillus thuringiensis Berliner variety kurstaki (Foray 48 F) and gypsy moth nuclear polyhedrosis virus (Gypchek) application on ant communities. Ant samples were also compared by sampling years. Pitfall traps were operated for 45 wk during summers of 1995–1997. A total of 31,732 ants was collected from pitfall traps; they belonged to four subfamilies, 17 genera, and 31 species. The ant species richness, diversity, abundance, and species composition did not change as a result of the treatments. Further tests of ant abundance were suggested because the test power was low. Comparisons between sampling years showed a very similar species composition and species evenness. There was a significant decrease in ant abundance in the third year of sampling, which might have been caused by over-trapping. Some rare species did not appear in the second and third year of sampling.

Quantitative Analysis of a Pathogen-Induced Premature Collapse of a “Leading Edge” Gypsy Moth (Lepidoptera: Lymantriidae) Population in Virginia

The population dynamics of a “leading edge” (= at the edge of the expanding gypsy moth invasion) gypsy moth, Lymantria dispar (L.), population was monitored for 3 years (1995–97), with emphasis on the interactions of the gypsy moth nuclear polyhedrosis virus (LdNPV) and the fungus Entomophaga maimaiga Humber, Shimazu, & Soper. Gypsy moth populations in the woodlots varied from very sparse to high (potentially defoliating) levels. LdNPV was strongly density dependent, being confirmed only from the higher populated woodlots. In contrast, the fungus was similarly active in both sparse and highly-populated woodlots. In 1995, the fungal epizootic developed late in the season, with most larvae succumbing during stadia 5–6 and producing mainly resting spores (azygospores). Estimated mortality due to fungus averaged 68% in high-density plots and 85% in low-density plots. LdNPV mortality occurred in a two-wave epizootic, although second-wave LdNPV mortality was undoubtedly reduced because of the reduction of late-season larvae due to fungus activity. Estimated mortality due to LdNPV averaged 14% in highly-populated plots and 1% in low-population plots. In 1996, high levels of fungal-induced mortality occurred earlier in the gypsy moth season than in the previous year. Most gypsy moth larvae in 1996 died in a mid-season wave of fungal-induced mortality, with necropsied cadavers containing only conidia. This resulted in relatively few larvae surviving to late instars. At this time, a second wave of fungus-induced mortality occurred, with over half of the necropsied cadavers containing resting spores. The depletion of the gypsy moth populations by the fungus in 1995 resulted in a greatly reduced first wave of LdNPV in all plots in 1996, and perhaps due to the early appearance of the fungus in 1996, LdNPV was nearly absent from late-season larvae collected from all plots. In 1997, gypsy moth populations were uniformly low, and no dead larvae were found in any of the plots.

Field Evaluation of an Improved Formulation of Gypchek (a Nuclear Polyhedrosis Virus Product) Against the Gypsy Moth (Lepidoptera: Lymantriidae)

Prior to 1994, Gypchek® (USDA Forest Service, Washington, DC), the gypsy moth nuclear multicapsid polyhedrosis virus (LdMNPV), was used in operational programs against gypsy moth Lymantria dispar (L.) dispersed in a standard molasses-lignosulfonate tank mix and applied twice at the rate of 5 × 1011 polyhedral inclusion bodies (PIB) per ha per application in a volume of 19 liters per ha. In 1995, we evaluated a commercially-produced carrier and operational options that would make Gypchek application more efficient and less costly without reducing efficacy. Specifically, the standard tank mix formulation and application procedure was compared against a premixed commercial carrier, Carrier 038 (Novo Nordisk, Franklinton, NC) applied by three different application options. Option 1 consisted of double applications of Gypchek at the rate of 5 × 1011 PIB per ha per application in volumes of 9.5 liters per ha. Option 2 was identical to Option 1 except that application volume was reduced to 4.8 liters per ha. Option 3 consisted of a single application of Gypchek dispersed in 9.5 liters per ha at the rate of 1 × 1012 PIB per ha. There was also a fifth treatment consisting of unsprayed control plots. All treatments were evaluated in replicated 4-ha forest plots in southwestern Virginia. Levels of LdNPV-induced mortality, of larvae collected live 6 to 11 days after treatment, among treatments receiving a double application were not significantly different at α = 0.05 from such mortality resulting from the single application of Gypchek in Carrier 038. However, both of the double-application treatment options (but not the single application option) of Gypchek dispersed in Carrier 038 had significantly higher levels (α = 0.05) of LdMNPV than the double-application treatment of Gypchek dispersed in the standard tank mix. Defoliation was significantly different among the four Gypchek treatments, but all were significantly lower than the controls. These results indicated that all three options using Carrier 038 provided a level of efficacy equal to or better than the standard tank mix formulation applied twice at 19 liters/ha. Economic assessment indicated that the single application option was more efficient and/or less expensive than the other options.

An Evaluation of the Residual Activity of Traditional, Safe, and Biological Insecticides Against the Gypsy Moth

We evaluated the direct and the residual efficacy of selected traditional, safer, and biological insecticides that are either registered or are candidates for registration for use by arborists and nurserymen in Integrated Pest Management (IPM) programs for gypsy moth (Lymantria dispar} management in urban settings. The study compared 5 biological insecticide treatments (1 Bacillus thuringiensis[Bf] and 4 gypsy moth nuclear polyhedrosis virus [NPV] treatments) and 2 reduced-risk insecticides (neem and tebufenozide) against 2 commonly used standard insecticides (diflubenzuron and cyfluthrin). Significant details pertaining to the use of the specific control materials were clarified in support of a decision matrix around which an IPM system can be formulated for use by arborists and nurserymen. The standard insecticides, cyfluthrin and diflubenzuron, and the ecdysone agonist tebufenozide, demonstrated excellent activity against all instars in both a 1 - hour residue study and a 35-day residue study, Bt was clearly more effective against second instar larvae than against fourth instar larvae and lost significant activity against the gypsy moth after 7 days. The efficacy of the neem product was similar to that of Bt in that it controlled younger instars better than it did older instars. Although its speed of action was slower than that of Bt, it remained highly active against gypsy moth 21 days after treatment. NPV without the activity enhancer Blankophor BBH gave significant levels of control for all 4 larval instars fed on 1 -hour residues, although mortality was higher for younger instars than for older instars. Residual effectiveness was significantly reduced after 1 day. The addition of Blankophor BBH to the NPV tank mix led to improved kill in the 1-hour study and to vastly improved residual activity (up to 35 days).

Fungal and Viral Epizootics in Gypsy Moth (Lepidoptera: Lymantriidae) Populations in Central New York

Abstract The activity of the gypsy moth fungal pathogen Entomophaga maimaiga was documented from 1991 to 1996 in central New York. This fungus had been introduced to the area in 1990 but also generally spread throughout the region in 1990–1992. In 1991, gypsy moth populations were abundant in 8 mixed hardwood plots (mean ± SE = 15,295 ± 4373 egg masses/ha), the gypsy moth nuclear polyhedrosis virus (LdNPV) was the most important cause of larval mortality by microorganisms, and by the end of the season, populations had decreased to 6875 ± 1345 egg masses/ha. During 1991, E. maimaiga -infected larvae were found at 7 of 8 plots causing 0–37% infection but this was not associated with 1990 E. maimaiga infection levels. In 1992, the major cause of larval mortality by microorganisms was E. maimaiga, with infection levels ranging from 64 to 98%; LdNPV was also present at all 11 plots sampled. At lower density plots in 1992, E. maimaiga infections only increased dramatically during 5th and later instars. In higher density plots, 16 and 24% of 2nd and 3rd instars per the two early June sample dates were infected by E. maimaiga but infection levels once again peaked during later instars, although earlier in higher than lower density sites. During 1992, more cadavers of 4th and 5th + instars produced resting spores in the higher density plots than in the lower density plots, suggesting increased secondary transmission by conidia actively ejected from cadavers. The amount of rain falling during the periods of time that larvae were active differed by year; LdNPV was the dominant pathogen during the dry 1991 spring, while E. maimaiga flourished during 1992, when rain fell at approximately normal levels. From 1993 to 1996, gypsy moth populations remained low, with almost no LdNPV infections recovered, and E. maimaiga infections increased only after larval densities increased.

Fluorescence and Relative Activities of Stilbene Optical Brighteners as Enhancers for the Gypsy Moth (Lepidoptera: Lymantriidae) Baculovirus

Eight structurally related stilbene optical brighteners were compared as enhancers for the gypsy moth nuclear polyhedrosis virus (LdNPV). Five of the 8 brighteners acted as activity enhancers (Blankophor HRS, P167, BBH, RKH, and Tinopal LPW); but Blankophor BSU, DML, and LPG did not enhance the activity of LdNPV. The most effective brighteners (BBH, RKH, and LPW) reduced LC50s from 800- to 1,300-fold. LT50s were influenced by some brighteners (I-IRS, LPW, BBH, RKH) but not by others (LPG, DML, BSU). All 8 brighteners exhibited fluorescence, which was concentration dependent. The most fluorescent brighteners were LPW, BBH, RKH, and P167, and the least fluorescent brighteners were LPG and DML. In general, the most active brighteners (i.e., those exhibiting the greatest viral enhancement) tended to exhibit the greatest fluorescence, and the least active brighteners tended to exhibit the least fluorescence. Although pHs of the brighteners ranged from 7 to 10, no correlation was found between pH and activity enhancement.

Potential Enhancement of the Gypsy Moth (Lepidoptera: Lymantriidae) Nuclear Polyhedrosis Virus with the Triterpene Azadirachtin

Second-instar gypsymoth, Lymantria dispar (L.), larvae were placed on semisynthetic diet and white oak, Quercus alba L., seedlings that had been surface-treated with azadirachtin and gypsy moth nuclear polyhedrosis virus. Both treatments affected larval development (weight gain and molting) and survival. When consumed together, larvae died significantly faster compared with larvae, which consumed only azarurachtin or virus. The combination also resulted in lowered larval survival compared with that observed when only 1 material was consumed. The combination of azadirachtin and virus should result in good foliage protection if used against gypsy moth larvae. However, the addition of azadirachtin to viral formulations could also result in less virus being produced within the larval cadaver and released into the environment because the affected larvae are smaller.

Host Range of the Gypsy Moth (Lepidoptera: Lymantriidae) Pathogen Entomophaga maimaiga (Zygomycetes: Entomophthorales) in the Field Versus Laboratory

Lepidopteran larvae were sampled in the field to determine levels of infection by the gypsy moth, Lymantria dispar (L.), fungal pathogen, Entomophaga maimaiga Humber, Shimazu & Soper. Lepidopteran larvae were reared from 7 plots in Virginia in which moderate density gypsy moth populations simultaneously exhibited from 40.8 to 97.5% E. maimaiga infection. From a total of 1,511 larvae from 52 species belonging to 7 lepidopteran families in 4 superfamilies, only 2 individuals, 1 of 318 forest tent caterpillars, Malacosoma disstria Hiibner (0.3% infection), and 1 of 96 Catocala ilia (Cramer) (1.0% infection), became infected by entomophthoralean pathogens. Results from genomic DNA probes and bioassays confirmed that E. maimaiga had caused these infections. Laboratory studies yielded infection over a greater diversity of species, and percentages of infection from laboratory studies were higher than findings from the field for the 1 species infected in both the laboratory and field. At all sites, the gypsy moth nuclear polyhedrosis virus also was found, occasionally causing epizootics, but viral occlusion bodies were never found in nontarget Lepidoptera that died. In addition, 279 nontarget Lepidoptera belonging to 34 species in 8 families were collected and reared from areas with low density native gypsy moth populations, and E. maimaiga infections were not found in these nontarget hosts, although E. maimaiga was active in gypsy moth populations. A survey of lepidopteran cadavers collected from 1989 to 1995 containing entomophthoralean spores documented E. maimaiga infections in 3 species of lymantriids. The Lepidoptera-specific North American endemic entomopathogen Entomophaga aulicae (Reichardt in Bail) Humber, which is morphologically identical to E. maimaiga, was found in 1 geometrid species, 1 notodontid, 2 species of arctiids, and 1 introduced lymantriid, but in none of the gypsy moth larvae tested. Our results demonstrate that data from laboratory bioassays are poor estimates for predicting nontarget impact.

Blankophor BBH as an Enhancer of Nuclear Polyhedrosis Virus in Arborist Treatments Against the Gypsy Moth (Lepidoptera: Lymantriidae)

Doses of a commercial candidate formulation of gypsy moth nuclear polyhedrosis virus (LdMNPV) were applied with and without several concentrations of an enhancing adjuvant, Blankophor BBH., to individual trees against natural gypsy moth, Lymantria dispar (L.), populations. Amounts of Blankophor BBH adhering to foliage after application were measured at 1,322, 227, and 37 µg/g dry weight of leaf for the 0.5, 0.1, and 0.02% treatments, respectively. The highest dose of the candidate formulation used without the adjuvant failed to increase significantly 1st-generation after-treatment LdMNPV mortality (direct infection caused by feeding on applied virus) above background levels, to reduce late season (instars 5 and 6) larval populations in treated trees or to provide significant foliage protection. However, Blankophor BBH added to the tank mix at concentrations of 0.5 or 0.1% (wt: vol) resulted in significantly increased levels of 1st-generation after-treatment LdMNPV, significantly reduced late-season larval populations, and significant levels of foliage protection, compared with untreated control trees. The resulting recommended tank mix (0.1% Blankophor BBH and 2X 1010 PIBs per 75 liters final spray solution per tree) should give excellent foliage protection against gypsy moth at a cost of about $3 per tree.

Introduction and Establishment of Entomophaga maimaiga, a Fungal Pathogen of Gypsy Moth (Lepidoptera: Lymantriidae) in Michigan

In 1991, late instars of gypsy moth, Lymantria dispar (L.), were sampled and diagnosed for infections of the pathogenic fungus Entomophaga maimaiga Humber, Shimazu & Soper and for gypsy moth nuclear polyhedrosis virus (NPV) at 50 sites in Michigan. Approximately 1,500 larvae were collected and reared from these sites, and no infections of E. maimaiga were detected. From 1991, to 1993, we tested the efficacy of 2 inoculative-release methods for E. maimaiga in replicated plots at 3 research sites by relocating soil containing E. maimaiga resting spores from Massachusetts to Michigan or by releasing inoculated larvae onto boles of trees. In the 2nd yr after introduction, E. maimaiga became established (9-40% infection) where both inoculation methods were used, and a low level of infection was detected in control plots (0.5-2.4%). In the 3rd yr, epizootics of E. maimaiga occurred at all 3 research sites, with the incidence of infection ranging from 20 to 99% in both treated and control plots. Infection levels were correlated with precipitation and relative humidity greater than or equal to 90% for 2 wk preceding larval sampling. In 1993, egg mass densities at the 3 E. maimaiga study sites averaged 3- to 10-fold lower than in adjacent oak forest. We found that it is easy to introduce E. maimaiga to new locations even in the midst of an epizootic of gypsy moth NPV and that E. maimaiga reduces gypsy moth populations to levels lower than that caused by NPV alone.

Effects of pH, Temperature, and Ultraviolet Radiation on the Activity of an Optical Brightener as a Viral Enhancer for the Gypsy Moth (Lepidoptera: Lymantriidae) Baculovirus

The optical brightener, Tinopal LPW, was subjected to different pHs, temperatures, and to ultraviolet (UV) radiation. Tinopal LPW was stable at pHs ranging from 3.0 to 10.4, at temperatures of 121° C for 5 min, and at UV exposures (254, 302, and 360 nm) for periods up to 7 d. These treatments did not adversely affect the activity of Tinopal LPW as an enhancer for the gypsy moth nuclear polyhedrosis virus.

Rainfall Effects on Transmission of Gypsy Moth (Lepidoptera: Lymantriidae) Nuclear Polyhedrosis Virus

We explored the action of rain on the translocation of the gypsy moth nuclear polyhedrosis virus (LdNPV) at tree, branch, and leaf level. Artificial rainfall was used to simulate naturally occurring rainfall on leaves contaminated with 1st-instal gypsy moths, Lymantria dispar (L.), which had died of LdNPV. Bioassays using larvae in mesh bags on originally contaminated branches and branches below indicated that rainfall is effective in moving virus from branch to branch. This result was confirmed by an experiment using similar methods and naturally occurring rainfall. To examine this effect at the level of the leaf, we bioassayed leaf disks extracted from leaves with and without cadavers. Mortality of test larvae in leaf disk bioassays was strongly correlated with the presence of a cadaver on a leaf, but not confined to disks with cadavers. Mortality caused by non-LdNPV factors was also associated with consumption of a cadaver.

Modelling the epizootiology of gypsy moth nuclear polyhedrosis virus

Abstract Qualitative understanding of the dynamics of epizootics of the nuclear polyhedrosis virus of gypsy moth has become complete enough to justify attempts to quantitatively predict the timing and intensity of epizootics within a season. In earlier work (Dwyer and Elkinton, 1993), we compared the predictions of a simple differential equation model derived from Anderson and May (1981) to time series of virus mortality in each of eight gypsy moth populations (Woods and Elkinton, 1987). The model's predictions were very accurate for high density populations, but seriously under-estimated virus mortality in low density populations. Here we compare the predictions of the simple model to those of the gypsy moth life system model (GMLSM, Sheehan, 1985; Colbert and Racin, 1991), a highly complex computer simulation of gypsy moth population dynamics and forest stand growth that incorporates much of the existing knowledge of the many factors influencing gypsy moth populations. In particular we looked at two different versions of the GMLSM that incorporate two different models of virus transmission. One was identical to that of the simple model (Anderson and May, 1981; Dwyer and Elkinton, 1993), in which the rate of transmission was a constant (the transmission coefficient) times the product of the densities of healthy larvae and the densities infectious virus particles on foliage. The other approach, developed by Valentine and Podgwaite (1982) was a detailed model of production and consumption of infective particles on foliage. The model took account of age-related changes in the amount of foliage consumed and the variation in susceptibility of larvae to virus (LD50). The Anderson and May version of the GMLSM performed about as well as the simple differential equation model, but only for values of the transmission coefficient about 250 times higher that those we had determined experimentally (Dwyer and Elkinton, 1993). The Valentine and Podgwaite (1982) version of the GMLSM gave a much better fit, but only for values of LD50 that were 100 times higher than those determined experimentally. Future research will focus on efforts to refine our understanding of virus transmission in order to explain and reduce the discrepancies between model predictions and observed mortality from virus in fieldpopulations.

Enhanced Infectivity of Occluded Virions of the Gypsy Moth Nuclear Polyhedrosis Virus for Cell Cultures

The occluded form of baculoviruses is much less infectious to cell cultures than the extracellular virus (ECV). In studies using alkaline solutions or insect gut fluids, from 3,600 to 54,000 occlusion bodies (OBs) were needed per infectious unit. Yet there are reasons for wanting to use OBs, namely, for monitoring the efficacy of polyhedra and to avoid problems associated with long-term passage of the ECV. In the present study, gypsy moth nuclear polyhedrosis virus OBs were dissolved in a sodium bicarbonate/sodium chloride solution and used to infect the gypsy moth fat body cell line (IPLB-LdFBc1). Using 27 mM Na 2CO 3 and 54 mM NaCl, the optimum time of dissolution was 30 min and approximately 1200 OBs were necessary to obtain one infectious unit. In addition, treatment of the dissolved OBs with 90 μg/ml trypsin for 2 hr resulted in only 21 OBs being necessary to obtain one infectious unit, an improvement of over 50-fold. Also, comparison with other cell lines showed two embryonic cell lines (IPLB-LdEp and IPLB-LdEIta) to be more susceptible to dissolved OBs. However, the infectivity to these other cell lines was not improved by trypsinization of dissolved OBs. Infection of fat body cell cultures through multiple passages using dissolved and trypsinized OBs still resulted in a decline in OB productivity over time but to a lesser degree than that with ECV. The same studies showed no increase in few polyhedra (FP) mutants when the virus was passed 15 times using polyhedra-derived virus, compared with an approximately 20% increase in FP mutants when ECV was used.

Effect of Neem Seed Extract upon the Gypsy Moth (Lepidoptera: Lymantriidae) and Its Nuclear Polyhedrosis Virus

Neem seed extract inhibited growth and development of gypsy moth, Lymantria disbar (L.), larvae. Untreated control larvae increased their weight by ≍40-fold by day 14, whereas insects treated with 0.10% neem and 1.00% neem weighed ≍30% and ≍4%, respectively, of the average weight of the untreated larvae. By day 14, 99% of the controls were in the fifth stage and 1% were prepupae. After treatment with 0.10% neem almost one-third of those larvae were still in the fourth stage, whereas larvae treated with 1.00% neem were still in the second and third stages. Neem extracts had little, if any, effect upon viral activity, as measured by LC50s. The addition of neem extract to the gypsy moth nuclear polyhedrosis virus, however, resulted in faster virus-caused mortality.