Ralph E. Webb

Aphid Alarm Pheromone: Isolation, Identification, Synthesis

A broadly interspecific aphid alarm pheromone was isolated from several economically important species of aphids and identified as trans-β-farnesene.

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-...

Nuclear Polyhedrosis Virus of the Gypsy Moth (Lepidoptera: Lymantriidae): Potency and Effects of Selected Adjuvants on Insect Feeding Behavior

The potency of two formulations of the nuclear polyhedrosis virus of the gypsy moth (LdMNPV) was evaluated in the laboratory. Both formulations were prepared with the same batch of LdMNPV produced in live insects by the USDA Forest Service. A Forest Service-recommended tank-mix preparation (LdMNPV, molasses, ultraviolet light screen, and sticker in water) was found to be about 20 times more potent than an experimental wettable powder preparation. The wettable powder also deterred feeding; the 20-fold difference in potency, though, is based on actual doses consumed. The addition of a stilbenedisulfonic acid derivative, Blankophor BBH, to the tank-mix and wettable powder preparations at a concentration of 1% (wt./vol.) reduced the LD50s by 42- and 214-fold, respectively. Blankophor BBH was also a moderate feeding deterrent to gypsy moth, Lymantria dispar (L.), larvae which could limit its efficacy as an enhancer of the virus. However, the addition of molasses to Blankophor BBH at least partially overcame th...

Control of Third and Fourth Instar Gypsy Moth (Lepidoptera: Lymantriidae) with Gypchek Combined with a Stilbene Disulfonic Acid Additive on Individual Shade Trees1

The efficacy of the gypsy moth (Lymantria dispar (L.)) nuclear polyhedrosis virus (LdMNPV), Gypchek, in combination with a stilbene disulfonic acid additive, Blankophor BBH, was evaluated against third and fourth-instar gypsy moth in 1992. Treatments were applied with hydraulic ground equipment to plots of one to three oak trees each in a gypsy moth-infested woodlot on the eastern shore of Maryland. An analysis of larvae collected from the plots revealed that the plots treated with LdMNPV and Blankophor BBH had significantly (P < 0.05) more larval mortality and significantly lower LT50 values than did plots treated with LdMNPV alone. Additionally, Blankophor BBH applied alone appeared to interact with native virus present in the field plots and significantly (P < 0.05) increased larval mortality when compared with untreated plots. The implications of these results for the potential use of LdMNPV in combination with a stilbene disulfonic acid additive are discussed.

Deletion of v-chiA from a Baculovirus Reduces Horizontal Transmission in the Field

ABSTRACT Nucleopolyhedroviruses (NPVs) can initiate devastating disease outbreaks in populations of defoliating Lepidoptera, a fact that has been exploited for the purposes of biological control of some pest insects. A key part of the horizontal transmission process of NPVs is the degradation of the larval integument by virus-coded proteins called chitinases, such as V-CHIA produced by the v-chiA genes. We used recombinant and naturally occurring strains of the Lymantria dispar NPV (LdMNPV) to test horizontal transmission in the field, release of virus from dead larvae under laboratory conditions, and cell lysis and virus release in cell culture. In the field, strains of LdMNPV lacking functional v-chiA genes showed reduced horizontal transmission compared to wild-type or repaired strains. These findings were mirrored by a marked reduction in released virus in laboratory tests and cell culture when the same strains were used to infect larvae or cells. Thus, this study tests the pivotal role of liquefaction and the v-chiA gene in field transmission for the first time and uses complementary laboratory data to provide a likely explanation for our findings.

Hydraulic spray application of Gypcheck as a homeowner control tactic against gypsy moth (Lepidoptera: Lymantriidae).

Gypsy moth, Lymantria dispar L., nuclear polyhedrosis virus (NPV) was applied by ground equipment at the rate of 2.5 × 1012 polyhedral inclusion bodies (PIBs) per ha to the lower half of ten trees...

Comparison of aerially-applied Gypchek strains against gypsy moth (Lepidoptera: Lymantriidae) in the presence of an Entomophaga maimaiga epizootic

The standard strain (LDP-226) of Gypchek®, a nucleopolyhedrovirus product registered by the USDA Forest Service against the gypsy moth, Lymantria dispar (L.), was compared against a strain, LdMNPV-203NL (NL = nonliquefying), that was developed for production in cell culture. Both strains were applied by air to U.S. government property in Prince Georges Co., MD, in early May 2003 at the rate of 1 x 1012 occlusion bodies per ha. The two goals of the study were (1) to compare the first and second wave effects of the two strains against gypsy moth populations; and (2) to delineate the combined effects of the applied virus and the expected epizootic of the gypsy moth specialist fungal entomopathogen Entomophaga maimaiga Humber, Shimazu, and Soper. Heavy rainfall in May and June preceded a massive epizootic of E. maimaiga, whose effects did not mask the first wave of viral mortality. When the effect of application sequence was considered, it was concluded that the two strains were equivalent in their first-wave impacts. High fungal-induced mid and late-season gypsy moth larval mortality suppressed the second wave of virus at all evaluation sites. There were no obvious differences in the second waves engendered by the two LdNPV strains in the greatly reduced late-instar larval population.

Effects of spined soldier bug (Hemiptera Pentatomidae) augmentation and sticky barrier bands on gypsy moth (Lepidoptera: Lymantriidae) density in oak canopies

The effects of sticky barrier bands, augmentative releases of the spined soldier bug, Podisus maculiventris (Say), and the deployment of P. maculiventris pheromone on gypsy moth, Lymantria dispar (L.), larval density in the canopy of oak trees were tested. Sticky barrier bands used alone reduced larval gypsy moth density by ≈35%. The release of 5,810 P. maculiventris nymphs per tree or the deployment of P. maculiventris pheromone to trees on which sticky barrier bands had been applied had no additional effect on gypsy moth larval density. None of the treatments affected the number of gypsy moth egg masses produced. Significantly more P. maculiventris adults were observed on trees with the pheromone, but higher numbers of nymphs were not subsequently observed on these trees. Counts of gypsy moths beneath burlap bands prior to gypsy moth pupation were about four times higher on unbanded than on banded trees, but counts of pupae beneath burlap bands did not differ between treatments.

Destruction of Gypsy Moth Egg Masses (Using Surfactants, Detergents, Oils or Conventional Insecticides) for Quarantine and Community Action Programs

A series of studies were conducted, beginning in 1976, at the Otis Methods Development Center, Otis ANGB, MA, and beginning in 1982 at the Beltsville Agricultural Research Center, Beltsville, MD, t...

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.