Control of low-density gypsy moth (Lepidoptera: Lymantriidae) populations by mating disruption with pheromone

This four-year study demonstrated that low-density populations of the gypsy moth,Lymantria dispar (L.), were effectively suppressed by annual aerial application of 75 g of racemic disparlure per hectare formulated in plastic laminate flakes. These tests also showed that, when plots were treated with 150 g of pheromone per hectare in 1990 only and left untreated for the following three years, populations continued to be suppressed in 1991–1993 as compared with the controls. Although none of the plots were treated in 1994, population assessment continued and showed that the gypsy moth population density remained low in the plots that had been treated annually for the preceding four years. The laminate flakes released an average of 0.48 g disparlure per day per hectare from each of the two applications in 1990, and 0.72 g per day per hectare from the single application in each of the following three years (1991–1993). Only 27–40% of the applied pheromone dose was emitted during male moth flight.     

Gypsy moth (Lymantria dispar L.) attraction to disparlure enantiomers and the olefin precursor in the People's Republic of China

Pheromone traps baited with disparlure,cis-7,8-epoxy-2-methyl-octadecane, captured males ofLymantria dispar, the gypsy moth, at two widely separated locations in the People's Republic of China. The (+) enantiomer of disparlure attracted significantly more males than the racemate; addition of olefin reduced captures. The duration of the flight period was longer (eight weeks) and peaked earlier near Beijing than farther north near Dunhua (five weeks).Lepidoptera: Lymantriidae.     

Leaf phenolic inhibition of gypsy moth nuclear polyhedrosis virus Role of polyhedral inclusion body aggregation

Bioassays with nuclear polyhedrosis virus (NPV) administered to gypsy moth larvae on leaf disks from various tree species reveal strong viral inhibition by some tree species. Phenolic extracts from inhibitory tree leaves cause virus polyhedral inclusion bodies (PIBs) to form large aggregations. However, aggregated PIBs treated with leaf extracts and administered to larvae on laboratory diet (without phenolics) retain virulence. Our results suggest that leaf phenolics, especially hydrolyzable tannins, inhibit NPV infection, but may not act via aggregations formed in the foregut.     

Male confusion of the nun moth with disparlure at high and low population densities

The feasibility of using the synthetic sex pheromone, disparlure, as a mating confusant of the nun moth (Lymantria monacha L.) was investigated on wild populations occurring in outbreak proportions in Poland and in low density in Czechoslovakia. The size of experimental plots ranged from 1 to 12 hectares. The amounts of pheromone applied were 10 or 20 g/hectare. Three types of slow-release formulations of a racemic mixture of disparlure were tested: (1) a spray formulation with latex as a carrier, (2) a tubing of natural rubber, and (3) sawdust of a porous material used for making tips of fiber-tip pens. All three pheromone formulations prevented significant numbers (98.6–100% in the low density situation, 90–96.2% during the outbreak) of the males from locating a discrete source of pheromone (a trap containing synthetic pheromone or a female) during the whole flight period, indicating long-lasting efficiency of the formulations.     

Pheromone-mediated behavior of the gypsy moth

The pheromone-mediated behavior of gypsy moth males was studied in both natural and simulated populations in central Pennsylvania. Feral males released into 50-m-diam plots, each with 2 feral females around the perimeter, oriented initially to trees and not to females. Neither exposure to virgin females nor exposure to wicks baited with approx 6 mg disparlure affected the subsequent sexual activity of males released into the 0.2-hectare plots. Males released into untreated plots, following 24 hr exposure in an area treated with approx 37 g/hectare of microencapsulated disparlure, located and mated with feral females within 4 min after release. None of the released males was caught in disparlure-baited Delta traps. In the disparlure-treated plot none of the females was mated. Males within this treated plot continued to search actively but did not settle down on the bark surface and initiate short-range (< 15 cm) search behavior. In plots testing the effect of various ratios of baited wicks to virgin females on disruption, there was no evidence of mating disruption due to point-source confusion. There were no significant differences in the responses of feral males to either virgin females or the various portions of Hercon wicks placed out in 0.2-hectare plots. In a series of tests using feral virgin females given various treatments to alter their physical and chemical characteristics (i.e., removed wings, denuded abdomen, washed in xylene, etc.), all females elicited the full range of sexual behavior responses of the male moths in natural populations. Apparently, males stimulated by pheromone are capable of using a number of different additional stimuli to initiate and terminate short-range sexual behavior patterns. Lymantria dispar (L.); Lymantriidae: Lepidoptera.Authorized for publication on April 19, 1976 as paper no. 5066 in the journal series of the Pennsylvania Agricultural Experiment Station, Experiment Station Project No. 2044.     

Some chemical bases for gypsy moth,Lymantria dispar,larval rejection of green ash,Fraxinus pennsylvanica,foliage as food

Green ash is one of the few tree species rejected as food by larvae of the generalist gypsy moth,Lymantria dispar L. (Lepidoptera: Lymantriidae). Such rejection is based especially on chemicals present in green ash foliage. The gypsy moth larval feeding-inhibitory activity is contained in the ethyl acetate extractables of green ash foliage. Three representative columnchromatographed fractions of the extractables contained antifeedant activity. Individual fractions showed weaker antifeedant activity compared to the total ethyl acetate extractables. Acid hydrolysis of the extractables destroyed antifeedant activity and yielded feeding stimulant activity at higher concentrations. The aqueous extractables were not feeding-inhibitory. Compounds in the green ash extractables were separated by TLC, HPLC, CC, and GC.     

Capture of gypsy moth,Lymantria dispar (L.), andLymantria mathura (L.) males in traps baited with disparlure enantiomers and olefin precursor in the People's Republic of China

Pheromone traps baited with (+)-disparlure,cis-7,8-epoxy-2methyocta-decane, captured males ofLymantria dispar, L. monacha, andL. mathura in northeastern People's Republic of China.L. dispar responded to the addition of olefin to (+)-disparlure-baited traps in a negative doseresponse manner. Observations on site and seasonal capture ofL. dispar andL. mathura are discussed.Lepidoptera: Lymantriidae.     

Effects on behavior ofApanteles melanoscelus females caused by modifications in extraction,storage, and presentation of Gypsy moth silk kairomone

Choice experiments were performed to investigate details of femaleApanteles melanoscelus (Ratzeburg) behavior when exposed to gypsy moth silk kairomone [Lymantria dispar (L.)] and to host larvae when kairomone is present. Female parasites only responded to the kairomone when it had been placed on thin strands such as cotton fibers. Both gypsy moth silk and silk glands contain the same or similar kairomones. Silk gland extracts were more active than head, alimentary canal, or hemolymph extracts of host larvae. Female responses decreased when low concentrations of silk gland extract or small numbers of treated fibers were presented to them. Silk gland extract was stable when frozen for 2 weeks, heated to 100 °C for 0.5 hr, freeze dried, or treated with 95% ethanol. The active component was nondialyzable. Silk deposited on the substrate increased host contacts and oviposition attempts, more so if wider areas were covered with silk, and even if the areas having silk were separated from the host. A theory of host selection inA. melanoscelus is proposed.Hymenoptera, Braconidae. Lymantria dispar L. (Lepidoptera: Lymantriidae).     

Host selection byBlepharipa pratensis (Meigen), a tachinid parasite of the gypsy moth,Lymantria dispar L.

The host selection process ofBlepharipa pratensis (Meigen), a tachinid parasite of the gypsy moth,Lymantria dispar L., was investigated. Once in the host's habitat, and following contact with a recently damaged leaf edge (cut, torn, eaten), the fly orients perpendicular to the edge and moves back and forth with the front tarsi grasping the damaged edge. Oviposturing (oviposition intention) may occur. Leaf exudates appear to arrest the fly on the leaf and increase tarsal examination (searching). If an edge of a gypsy moth-eaten leaf is contacted, oviposition usually occurs. Significantly more eggs are laid when host-browsed foliage is encountered, compared to mechanically cut or damaged foliage, indicating response to a cue left by the host during feeding. The number of host-damaged leaf clusters in an area significantly enhances oviposition there; in field-cage tests, significantly more eggs (7911) were laid in simulated-crown areas with all clusters browsed, compared to the adjacent areas containing 1/2 browsed (4200 eggs) and undamaged clusters (2209 eggs). A host selection sequence is suggested and discussed.     

Apple foliage enhances mating disruption of light-brown apple moth

Uptake and release of pheromone and behavioral inhibitor ofEpiphyas postvittanna by apple leaves was tested using field electroantennograms (EAG), trap catches to synthetic lures and virgin females, and chemical analysis. Trap catches in single apple trees (N=3) were monitored for six cycles of six days' duration, using delta traps baited with synthetic pheromone. Polyethylene dispensers (0, 1, 10 per tree) releasing pheromone and inhibitor were present for only the first three days of each cycle. Application of 10 dispensers per tree resulted in complete disruption of trapping, which continued for one day after dispensers were removed. Over the three nights following the removal of the dispensers (days 4–6), trap catch was 0, 10, and 15% of the control catch. In contrast, the presence of only one dispenser per tree led to 0–20% of control catches, but on the three nights following dispenser removal catches were 35, 40, and 80% of the control catch. Field EAGs indicated significantly higher relative pheromone concentrations in the trees with 10 dispensers present, compared to trees with single dispensers, but removal of dispensers produced no detectable treatment effect compared to the control trees one day after dispenser removal. In a second experiment, releases of marked male moths into apple orchard plots following the removal of polyethylene dispensers (1 hr earlier that day) resulted in significantly lower catches in traps baited with virgin females in blocks that had been treated, compared to controls. Recovery of pheromone by solvent washing of leaves loaded with 50 µg of the main component of the sex pheromone (1.26 µg/cm²) was low (2.5%). Leaves held in a pheromone-saturated atmosphere were loaded with 0.045±0.007 µg pheromone/cm². Analysis of apple leaves taken from a pheromone-treated tree at different distances from the pheromone dispenser showed a decay of the pheromone load per square centimeter with increasing distance from the dispenser, as previously indicated by EAG.     

Effect of pheromone concentration on organization of preflight behaviors of the male gypsy moth,Lymantria dispar(L.)

Male gypsy moths (Lymantria dispar L.) in a wind tunnel at 24° respond to decreasing dosages (1 g to 0.1 pg) of (+)-cis-7,8-epoxy-2-methyloctadecane with a decrease in probability of wing-fanning, an increase in wing-fanning latency, and an increase in the number of behaviors (body jerks, antennal twitches, steps, and wing tremors) preceding fanning. Males initiating any behavior prior to wing-fanning had a 70% probability of wing-fanning and 97% of the males that wing-fanned eventually flew. The sequence of behaviors from quiescence to flight is not organized in a hierarchy, as this concept is used in ethology, nor is it dependent upon the concentration of pheromone. The time-average threshold concentration of pheromone for response of ca. 90% or more quiescent males is ca. 1.9 × 10^–17 g/cm³ over < 0.3 min.Lepidoptera: Lymantriidae.Michigan Agricultural Experiment Station Journal Article No. 10263.     

Orientation behavior and effect of experience and laboratory rearing on responses ofCotesia melanoscela (Ratzeburg) (Hymenoptera: Braconidae) to gypsy moth silk kairomone

Cotesia melanoscela responds the same way to the silk of its host, gypsy moth larvae,Lymantria dispar L., whether or not it has previously been exposed to hosts. Parasites maintained in the laboratory for six or 25 generations also responded similarly, suggesting that orientation behavior is not modified by laboratory rearing. Details of silk-related orientation behavior were analyzed by tracing paths of female parasites when on or off silk-covered substrates. Females made 31 ° average turns every 0.5 cm whether or not they were examining silk. They tended to turn back onto a silked area when encountering a border, and their speed of movement when not examining silk was about three times higher than when examining silk.     

Apparency of pulsed and continuous pheromone to male gypsy moths

Quiescent male gypsy moths (Lymantria dispar) exposed in a wind tunnel to either pulsed (0.5-, 2- or 5-sec on, followed by a two-fold time interval off) or continuous streams of synthetic pheromone responded similarly in the proportions and latencies of wing fanning. Similarly, upwind anemotactic flight tracks in pulsed (1-sec on and 1-sec off) and continuous plumes of pheromone were indistinguishable. These data suggest that in the gypsy moth (1) pulsed pheromone stimuli would not lower the threshold, despite the improvement in the signal-to-noise ratio; and (2) temporal modulation of the pheromone plume at 1-sec intervals does not alter the preprogrammed upwind flight pattern.Journal paper No. 10916 of the Michigan State University Agricultural Experiment Station.     

On the persistence of disparlure in the human body

Response of male gypsy moths from a sparse infestation in Italy to an observer apparently contaminated with disparlure at least two years previously is reported. Other examples of pheromone contamination of people or things are also recorded.Authorized for publication as paper No. 5946 in the Journal Series of the Pennsylvania Agricultural Experiment Station.The observations in Italy were made while the author was a Gastdozent at the Entomologisches Institute, Eidgenössische Technische Hochschule, Zürich, Switzerland.     

Diel periodicity and influence of age and mating on sex pheromone titer in gypsy moth,Lymantria dispar (L.)

The diel periodicity of sex pheromone titer from pheromone glands of femaleLymantria dispar is described. On the day of emergence (day 0), pheromone titer was generally low; means ranged from 1 to 4 ngcis- 7,8-epoxy-2-methyloctadecane during photophase and gradually increased to 8.4 ng over the course of scotophase. For day-1, -2, and -3 females, the diel fluctuations of titer were more pronounced. Lowest titers (5–9 ng) occurred 0–4 hr after lights-on, and peak titers (19–32 ng) were found 0–4 hr before lights-off. Comparison of the average daily titer among the different age groups (data pooled over six time points at 4-hr intervals) indicated that significantly less pheromone was extracted from glands of day-0 (4.5 ng) than day-1 (12.4 ng), day-2 (15.4 ng), or day-3 females (13.5 ng). No significant differences were found among the three older ages. Femalesin copula exhibited a rapid reduction in titer within the first 0.5 hr of mating initiation (7.6 ng vs. 19.5 ng from virgin females of similar age). After the second 0.5 hr, the reduction in titer was not nearly as marked, falling only to 4.5 ng. Twenty-four hours after mating, titer fell below the limits of detection (0.5 ng). All extracts from pheromone glands of virgin or mated females contained < 1.0 ng of the putative pheromone precursor, 2-methyl-cis-7-octadecene.     

Comparative distribution and persistence of disparlure in woodland air after aerial application of three controlled-release formulations

Disparlure, the gypsy moth sex pheromone, was aerially applied to three plots, using a different controlled-release formulation-gelatin microcapsules, flakes of plastic laminates, or hollow fibers-in each plot. Disparlure concentrations in air were measured intermittently over a 34-day period after application. Measurements were made at four heights above ground: 0.3,2,5, and 10m. Wind speed and air temperature were measured concurrently. Disparlure was emitted from the microcapsules and fibers at very high levels for the first day or two; thereafter, all three formulations produced gradually decreasing aerial concentrations. After 32–34 days, concentrations in all plots ranged from 1.5% to 15.5% of those on the first day, although most of the pheromone remained in the formulations. Results suggest that the effective life of all three formulations for mating disruption by atmospheric permeation would be near 30 days under the test conditions, with fibers likely to have the shortest life. Concentrations varied diurnally throughout the experiment, with highest levels generally between 1400 and 2200 hr each day. Concentrations were highest at the 10-m height with microcapsules and at the 0.3- and 10-m heights with flakes, but were similar at all heights with fibers. Biological implications of the results are presented.     

White alder and Douglas-fir foliage quality and interegg-mass influences on larval development of gypsy moth,Lymantria dispar

Individual families of gypsy moth collected from a single population exhibited different degrees of fitness when fed diets of white alder, a suitable broadleaf host, and Douglas-fir, an unsuitable conifer host. Members of families on diets of Douglas-fir had significantly lower survival, longer larval periods, lower pupal weights, and shorter pupal periods than members of the same families fed alder. Foliar nutritional quality, including nitrogen level and allelochemical composition (terpenes and phenols), was considered the key factor responsible for these differences. Growth parameters differed significantly for families within diet treatments, indicating that the genetic resources of a family did affect performance somewhat. The influence of a family's genetic resources on larval survival was most notable when larvae were under the greatest nutritional stress.     

Performance characteristics of a commercial controlled-release dispenser of sex pheromone for control of codling moth (Cydia pomonella) by mating disruption

Performance characteristics of polyethylene tube dispensers containing a mixture of (E,E)-8,10-dodecadien-1-ol (1), dodecan-1-ol (2), and tetradecan-1-ol (3) were evaluated for suitability as a mating disruptant for codling moth control. The rate of loss of pheromone component from a dispenser at any time was found to be described by the equation: –dP/dt=(k ₁ k ₂ +k _d)P whereP is the amount of pheromone component in the dispenser well;t is time;k ₁ is the ratio of the amount dissolved in the dispenser wall to the amount in the dispenser well;k ₁ is the ratio of the evaporation rate to the amount dissolved in the dispenser wall;k _d is the rate constant for chemical decomposition. The evaporation rate,E, of a pheromone component at any time was given by:E=k ₁ k ₂ P For all three components during the first three weeks,k ₁ decreased from ca. 0.25 to ca. 0.10 and was approximately constant thereafter. The decrease ofk ₁ with time may have been caused by weather-induced cross-linking of the polyethylene. Over timek ₂ was constant and was 1.27 ± 0.26 × 10^–3/hr for1, 1.96 ± 0.33 × 10su–3/hr for 2, and 0.31± 0.05 × 10^–3/hr for 3. Thek ₂ was zero for2 and3 and 6.96 × 10^–4 for1. After 150 days in an orchard in 1991, 95% of1 was lost from the dispensers (61% of the loss was by chemical decomposition and 39% by evaporation). The heat summation units in a Yakima valley orchard during 1991 were 4.7% above the average for the 1980–1991 period, while during 1990 they were the highest for this period (26% above average). After the first three weeks of dispenser aging, the regression line half-lives for1 for 1990 and 1991 were 31.0 and 35.1 days, respectively. The difference in temperature between 1990 and 1991 did not affect the half-life of1 very much because so much of the loss was from photochemically induced decomposition. Based on an estimate of the required minimum evaporation rate for mating disruption of 2 mg/ha-hr and a half-life of 35 days for1, 2345 dispensers/ha would be required for one application per season; 944 dispensers/ha for two applications per season; and 734 dispensers/ha for three applications per season. If a different emission rate of1 is required for reliable mating disruption, then the number of dispensers required would be changed proportionately.     

Effects of nitrogen and Douglas-fir allelochemicals on development of the gypsy moth,Lymantria dispar

Two experiments were conducted to examine the influence of foliar nitrogen, terpenes, and phenolics of Douglas-fir on the development of gypsy moth larvae. In the first experiment, foliar concentrations of nitrogen and allelochemicals were manipulated by fertilizing 3-year-old potted seedlings with 0 or 200 ppm nitrogen. Concentrations of foliar nitrogen (0.33–2.38%) were negatively correlated with the phenolics (15.8–24.4 mg/g). Sixth-instar larvae previously reared on current-year Douglas-fir needles were allowed to feed on these seedlings. Pupal weights (312.8–995.6 mg) were positively correlated with levels of foliar nitrogen, negatively correlated with amounts of foliar phenolics, and uncorrelated with terpene concentrations. In the second experiment, terpene and phenolic extracts from Douglas-fir foliage were incorporated at natural levels into artificial diets with high and low levels of protein nitrogen. Neonate larvae grew faster and were larger on the high nitrogen control diet (4.1–4.5%), however, fourth instars performed better on the control diet with low nitrogen levels (2.5–2.7%). Foliar terpenes incorporated into diet had little effect on neonate fitness, but may induce subtle physiological changes in later instar larvae. Phenolics, alone or in combination with terpenes, excessively suppressed growth and survival, with no individuals living through the fourth instar, regardless of the nitrogen level. Incorporating foliar phenolic extracts into artificial diet caused unnatural levels of toxicity and failed to clarify the effects of Douglas-fir phenolics on gypsy moth fitness. Foliar nitrogen is a key factor influencing gypsy moth development on Douglas fir, but may be mitigated to some degree by phenolics.