Western Hemlock Looper Research Articles

Asymmetric synthesis of sex pheromone of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst)

The western hemlock looper is an economically important defoliator of coniferous trees. Its sex pheromone has been synthesized in 36–50% total yield using the enantiomers of 2-methyloxiraneoxide as chiral sources. The key steps of this strategy involved CuI catalyzed ring-opening of chiral 2-methyloxiraneoxide, stereospecific inversion of secondary tosylate and Wittig coupling of the aldehyde with chiral phosphonium salt. The synthetic pheromones would be used to monitor and control this pest.

Insights into herbivore distribution and abundance: oviposition preferences of western hemlock and phantom hemlock loopers

AbstractKnowledge of the factors affecting host selection by herbivorous insects is essential to predictions of their distribution and abundance over landscapes. In the laboratory, we studied the oviposition preferences of two eruptive loopers (Lepidoptera: Geometridae) native to western Canada (western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), and phantom hemlock looper, Nepytia phantasmaria (Strecker)) for different species and condition of hosts. When offered a choice, phantom hemlock loopers laid nearly three times as many eggs on western hemlock, Tsuga heterophylla (Raf.) Sarg. (Pinaceae) as on either western redcedar, Thuja plicata Donn ex D. Don (Cupressaceae) or western white pine, Pinus monticola Douglas ex D. Don (Pinaceae). Western hemlock loopers were less specific, laying equal numbers of eggs on western hemlock and western redcedar, though fewer eggs were deposited on western white pine when compared with western hemlock. When offered western hemlock trees grown under different nutrient and shading regimes, phantom hemlock loopers preferred to oviposit on high nutrient hosts, irrespective of shading; western hemlock loopers exhibited a preference for high-nutrient hosts only if they were grown without shading. These patterns of host preference can be combined with information regarding forest composition to help quantify the conditional probability of western and phantom hemlock looper distibution and abundance.

Potential Impacts of Climate Change on Western Hemlock Looper Outbreaks

We calculated monthly soil moisture deficits from historical meteorological data from the south coast of mainland British Columbia to quantify warm and dry conditions at monthly and seasonal scales. Our main objective was to determine if climatic conditions antecedent to recorded outbreaks of western hemlock looper (Lambdina fiscellaria lugubrosa Hulst) may have triggered population growth. Periods of soil moisture deficits during the month of June were associated with the onset western hemlock looper outbreaks in the study area, as were warmer and drier conditions during the growing season two years prior to the first year of visible defoliation. Models of climate change predict that future summers in the Pacific Northwest will be warmer and potentially drier than present, and although other factors besides climate influence western hemlock looper population dynamics, the combined effects of more frequent droughts, changes in forest cover, and expanded range of western hemlock due to climate change may result in increased frequency, size and severity of outbreaks in the future.

Tree mortality caused by the western hemlock looper in landscapes of central British Columbia

An outbreak of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst) (Coleoptera: Geometridae), caused tree mortality in central British Columbia, Canada, to stands composed of alpine fir, Abies lasiocarpa (Hook.) Nutt., western hemlock, Tsuga heterophylla (Raf.) Sarg., white spruce, Picea glauca (Moench) Voss, and western red cedar, Thuja plicata Donn. After 4 years, high levels of tree mortality (51–96% of all trees with DBH ≥ 7.5 cm) occurred in areas of severe defoliation classifying this pest as a serious depletion agent of British Columbia forests. Tree mortality occurred rapidly, mostly within 2 years of the start of the infestation. Equations are provided to allow foresters to determine expected mortality levels with reasonable precision. A higher proportion of mortality occurs on alpine fir rather than on other species.

Pupal sampling of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst) (Lep., Geometridae) using burlap traps

Abstract: Three types of burlap traps were designed and tested for the western hemlock looper, Lambdina fiscellaria lugubrosa, in the interior of British Columbia from 1993 to 1994. While the first two trap types provided the means for examining the responses of pupating larvae to various layers of burlap band and pocket structure, the third trap type, which had the desirable burlap layers and structure, was used as a sampling tool for the insect. The effects of tree diameter, crown ratio, crown class, defoliation class and basal areas on trap capture appeared to vary with locations. However, a high correlation between trap capture and actual population density was consistently present. Therefore, trap capture can be used as an estimator of actual population density.

Forest roadside sampling of larvae and adults of the western hemlock looper, Lambdina fiscellaria lugubrosa

The roadside sampling method, in which sampling is conducted along a road has the advantage that large areas can be quickly surveyed. The method is particularly useful for forest areas where accessibility to trees within a stand can be a problem. In this study, larvae and adults of the western hemlock looper were sampled along forest roads and the data were examined with spatial statistics. The results indicated spatial continuity of insect counts along the forest roads, although the range and magnitude varied significantly between years and among sites. At Sugar Lake Forest Road, larvae and adults were spatially dependent within a distance of 7.25 km. In the three Vancouver watersheds, a significant spatial autocorrelation of male adult counts occurred when traps were up to 3 km apart. In addition, insect densities along the roads were closely related to those within the stands. The implications of these results to the management of the western hemlock looper are discussed.

Characterization of Nuclear Polyhedrosis Viruses from Three Subspecies ofLambdina fiscellaria

The eastern hemlock looper (EHL),Lambdina fiscellaria fiscellaria,the western hemlock looper (WHL),L. fiscellaria lugubrosa,and the western oak looper (WOL),L. fiscellaria somniaria,are closely related insects that are pests in Canadian forests. We have used restriction endonuclease (REN) and Southern blot analyses to characterize DNA of nuclear polyhedrosis viruses (NPVs) isolated from each of the three subspecies ofL. fiscellaria.REN analysis of EHL-NPV, WHL-NPV, and WOL-NPV DNAs revealed that they have nonidentical REN-banding patterns. NPV DNA extracted from WOL larvae collected from Douglas fir trees had a different REN pattern than NPV DNA extracted from WOL larvae collected from Garry oak trees. Hybridization of radiolabeled EHL-NPV genomic DNA revealed that the EHL- and WHL-NPVs share considerable DNA sequence similarity, as radiolabeled EHL-NPV DNA hybridized strongly with all WHL-NPV DNA bands. The EHL-NPV polyhedrin gene hybridized strongly with WHL-NPV DNA, but the hybridization patterns of the two NPVs were different. Very weak hybridization was detected between the EHL-NPV polyhedrin gene and DNAs of the two WOL-NPVs. Nucleotide sequence analysis revealed that the polyhedrin genes of EHL-NPV and WHL-NPV differ in sequence by only eight nucleotide substitutions (five third position and three second position changes, resulting in four amino acid substitutions). Phlyogeneitc analysis using the polyhedrin genes of EHL-NPV and WHL-NPV indicate that these two viruses cluster with the Group II NPVs as described by Zanotto, Kessing, and Maruniak (1993,J. Invertebr. Pathol.62,147).

Distribution Pattern and Sampling of Eggs of the Western Hemlock Looper (Lepidoptera: Geometridae) in Mature Western Hemlock Stands

An egg sampling study of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), was conducted in mature western hemlock stands from 1992 to 1994 in British Columbia, Canada. Egg density of the looper was homogenous within a tree crown, Suggesting that lower-crown sampling is effective for egg density estimation on the entire tree. Both the Taylor power law and the Iwao patchiness regression described egg distribution as aggregated. This aggregated distribution was further delineated as negative binomial distribution by chi-square test. Based on the Iwao model, the optimal sample size required to reach a predetermined precision level was calculated. To reduce egg-counting time, the relationship between mean egg density and proportion of lichen samples containing a specified number of eggs was established. The effect of tree height, diameter at breast height, crown width, crown length, and presence of heartrot on egg density was also examined. The results indicated no significant effect on egg density of these variables.

Pheromone Synthesis, CLXXIV. Synthesis of (5R,11S)‐5,11‐Dimethylheptadecane and (S)‐2,5‐Dimethylheptadecane, the Major and the Minor Components of the Sex Pheromone of the Geometrid Moth, Lambdina fiscellaria lugubrosa

Abstract(5R,11S)‐5,11‐Dimethylheptadecane (1), the major component of the female‐produced sex pheromone of the western hemlock looper (Lambdina fiscellaria lugubrosa), was synthesized by starting from the enantiomers of methyl 3‐hydroxy‐2‐methylpropanoate (3). (S)‐2,5‐Dimethylheptadecane (2), the minor and synergistic component of the pheromone, was also synthesized by starting from (S)‐citronellol (4).

Development of a Pheromone-Based Monitoring System for Western Hemlock Looper (Lepidoptera: Geometridae): Effect of Pheromone Dose, Lure Age, and Trap Type

A two-component pheromone blend containing a 1:1 (vol:vol)ratio of isomeric 5,1l-dimethylheptadecane and isomeric 2,5-dimethylheptadecane was tested in high-capacity Unitraps to monitor populations of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), throughout the coastal western hemlock and interior cedar hemlock biogeoclimatic zones of British Columbia. Rubber septa were loaded with each component at doses of 10, 100, 1,000, and 10,000 μ (1992) and 1 and 10 μ (1993). Males demonstrated a dosedependent response, except that captures in traps with the 2 highest doses (1,000 and 10,000μ) did not differ. Unitraps with 10-μ lures captured significantly more males than similarly baited sticky traps at the beginning of the flight and with 1- and 10-μ-baited lures at midflight. Both 1- and 10-μ lures maintained their attractiveness over the 3-mo flight season, which extends from mid-August through October, but catches in traps with l-μ lures were low. In all cases, >80% of the males were captured by the beginning of October. Seasonal trends in trap catches were not closely related to temperature. This research suggests that traps baited with 10-μ lures could be used to monitor populations and detect incipient outbreaks of the western hemlock looper.

Predictive Capabilities of a Pheromone-Based Monitoring System for Western Hemlock Looper (Lepidoptera: Geometridae)

Eggs, larvae, and pupae of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), were sampled and related to the numbers of male moths captured in pheromone-baited Unitraps at 27 (1992) and 34 (1993) study sites throughout the coastal western hemlock and interior cedar hemlock biogeoclimatic zones of British Columbia. Male moth catches in traps baited with 10 μg of both isomeric 5,1l-dimethylheptadecane and 2,5-dimethylheptadecane on a rubber septum lure were significantly correlated with larval and pupal counts within the same generation and were predictive of egg counts in the subsequent generation, suggesting that pheromone-baited traps could be used to monitor populations and predict future outbreaks.

Sex pheromone components of the spring hemlock looper,Lambdina athasaria (Walker) (Lepidoptera: Geometridae)

Two methylated hydrocarbons, 7-methylheptadecane (7) and 7,11-dimethylheptadecane (7,11), are female sex pheromone components of the spring hemlock looper (SHL),Lambdina athasaria (Walker). Compounds extracted from female pheromone glands were identified by coupled gas chromatographic-electroantennographic detection (GC-EAD) and coupled GC-mass spectrometry (GC-MS) in selected ion monitoring mode. In field trapping experiments, (7) and (7,11) by themselves were behaviorally inactive, but in combination attracted numerous male moths. (5,11)-Dimethylheptadecane (5,11) was detected in female SHL pheromone gland extracts, but did not enhance attraction to the binary blend of (7) and (7,11). The sex pheromone of SHL is related to that of congeneric eastern hemlock looper (EHL),Lambdina fiscellaria fiscellaria (Guen.) [(5,11) and 2,5-dimethylheptadecane (2,5)] and western hemlock looper (WHL),L.f. lugubrosa (Hulst) [(5,11), (2,5) and (7)]. Specificity of the pheromonal blend, spatial separation of coseasonal EHL and WHL, and temporal separation of sympatric EHL and SHL contribute to reproductive isolation.

Chirality of synergistic sex pheromone components of the western hemlock looperLambdina fiscellaria lugubrosa (HULST) (Lepidoptera: Geometridae)

Bakers' yeast reduction of (2E)-3-(2'-furanyl)-2-methyl-2-propenal yielded the synthetic intermediate, (2S)-3-(2'-furanyl)-2-methylpropanol, of high chiral purity (>97% ee) for the synthesis of the enantiomers of 2,5-dimethylheptadecane and 7-methylheptadecane, two synergistic sex pheromone components of the western hemlock looper (WHL),Lambdina fiscellaria lugubrosa Hulst. In electrophysiological bioassays, (7S)- but not (7R)-7-methylheptadecane elicited strong antennal responses by male WHL antennae. In field trapping experiments, addition of (7S)- but not (7R)-7-methylheptadecane to (5R,11S)-5,11-dimethylheptadecane, the major sex pheromone component of WHL, increased attraction. Attraction to (5R,11S)-5,11-dimethylheptadecane in combination with (7S)-7-methyiheptadecane was further enhanced by the addition of (5S)- but not (5R)-2,5-dimethylheptadecane. Similarly, attraction to (5R,11S)-5,11-dimethylheptadecane combined with (5S)-2,5-dimethylheptadecane increased when 7S- but not (7R)-7-methylheptadecane was added as a third component. We conclude that (7S)-7-methylheptadecane and (5S)-2,5-dimethylheptadecane are the synergistic sex pheromone components of WHL. The synthetic methodology described is applicable to the synthesis of chiral methyl-branched pheromones in other orders of the Insecta, particularly Coleoptera, Diptera and Orthoptera.

Chirality of 5,11-dimethylheptadecane, the major sex pheromone component of the hemlock looper,Lambdina fiscellaria (Lepidoptera: Geometridae)

Of the four possible stereoisomers of 5,11-dimethylheptadecane, the major sex pheromone component of the eastern hemlock looper (EHL),Lambdina fiscellaria fiscellaria Guen., and the western hemlock looper (WHL),Lambdina fiscellaria lugubrosa Hulst, (5R,11S)-5,11-dimethylheptadecane was the only stereoisomer eliciting electrophysiological responses by male EHL and WHL antennae. In field bioassays with EHL and WHL populations, traps baited with (5R,11S)-5, 11-dimethylheptadecane caught as many males as did traps baited with all four stereoisomers combined or a synthetic mixture of 5,11-dimethylheptadecanes. Catches in traps baited with the other three stereoisomers did not significantly differ from those in the unbaited control traps. We conclude that male antennae lack chemoreceptors for the other three stereoisomers of 5,11-dimethylheptadecane and hypothesize that only (5R,115)-5,11-dimethylheptadecane is produced by female EHLs and WHLs.

Sex pheromone of the western hemlock looper,Lambdina fiscellaria lugubrosa (Hulst) (Lepidoptera: Geometridae)

The sex pheromone of the western hemlock looper (WHL),Lambdina fiscellaria lugubrosa (Hulst), comprises three methylated hydrocarbons: 5,11-dimethylheptadecane (5,11), 2,5-dimethylheptadecane (2,5), and 7-methylheptadecane (7). Compounds extracted from female pheromone glands were identified by coupled gas chromatographic-electroantennographic (GC-EAD) analysis and coupled GC-mass spectroscopy in selected ion monitoring mode. In trapping experiments, (5,11) alone attracted male moths, but addition of either (7) or (2,5) significantly enhanced attraction. (5,11) combined with both (7) and (2,5) was significantly most attractive. (5,11) and (2,5) are also sex pheromone components of the eastern hemlock looper (EHL),Lambdina fiscellaria fiscellaria (Guen.). Although (7) is produced by the EHL, it is a pheromone component only in the WHL. It constitutes the first behaviorally active monomethyl-branched hydrocarbon to be found in a geometrid and is a novel lepidopteran sex pheromone component. The different 2- versus 3-component sex pheromone supports taxonomic division of EHL and WHL.

SAMPLING WESTERN HEMLOCK LOOPER PUPAE (LEPIDOPTERA: GEOMETRIDAE) USING BURLAP TRAPS

Burlap wrapped around western hemlock, Tsuga heterophylla (Raf.) Sarg., trees at breast height was used to trap pupae of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst). The number of pupae in the traps was highly variable and was not related to tree diameter or the surface area of the trap. There was a significant relationship between the number of viable pupae per trap and the number of healthy western hemlock looper eggs subsequently laid on lichen in the trees. Sample size requirements are presented.

CHAETOPHLEPSIS NASELLENSIS, A DIPTEROUS PARASITOID OF THE WESTERN HEMLOCK LOOPER (LEPIDOPTERA: GEOMETRIDAE)

AbstractPreserved material from 1962 field studies provided information on the habits and morphology of the tachinid parasitoid Chaetophlepsis nasellensis Reinhard. Parasitization of the larvae of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), continues over a 30- to 40-day period. Maggots issue from the host larvae and drop to the ground to pupate. The pupae normally overwinter, with adults emerging the following spring or summer. The early first-instar larva differs markedly from the late first-instar. The three instars can be distinguished on the basis of body length and the structure and form of the buccopharyngeal apparatus. The first and third larval instars and the puparium are distinctive enough to permit easy identification during studies of the western hemlock looper and associated loopers.

Toxicity of Selected Insecticides Applied to Two Defoliators of Western Hemlock

Thirteen insecticides were tested in a laboratory spray chamber on 4th and 5th instar hemlock sawfly, Neodriprion tsugae Middleton. Twelve exceeded DDT in toxicity at both LD50 and LD90. At LD50 the descending order of toxicity to combined groups of 4th and 5th instars was tetrachlorvinphos, resmethrin, fenitrothion, naled, mexacarbate, malathion, pyrethrins, dimethoate, propoxur, carbaryl, methomyl, trichlorfon, and DDT. Of 6 insecticides applied topically to 4th- and 5th-instar western hemlock looper, Lambina fiscellaria lugubrosa (Hulst), 5 exceeded DDT in toxicity at both LD50 and LD90. At LD50 the descending order of toxicity was pyrethrins, phoxim, mexacarbate, Dowco 217 (dimethyl-3,5,6-trichloro-2-pyridyl phosphate), fenitrothion, and DDT.

PATHOGENICITY TESTS OF NUCLEAR POLYHEDROSIS VIRUSES INFECTING THE EASTERN HEMLOCK LOOPER, LAMBDINA FISCELLARIA FISCELLARIA (LEPIDOPTERA: GEOMETRIDAE)

AbstractLarvae of the eastern hemlock looper, Lambdina fiscellaria fiscellaria (Guen.), are susceptible to a nuclear polyhedrosis virus as well as nuclear polyhedrosis viruses isolated from the western hemlock looper, L. f. lugubrosa (Hulst), and the western oak looper, L. f. somniaria (Hulst). The pathogenicity of these viruses was similar when tested on eastern hemlock looper larvae and it is suggested that the same virus infects the three subspecies. Resistance to the virus did not increase with age; second-, third-, and fourth-instar larvae were equally susceptible. The period from ingestion to death varied with concentration of virus and rearing temperature. Results of pathogenicity tests are given.

Carbaryl, Phosphamidon, and DDT Tests on the Western Hemlock Looper in Washington

Outbreaks of the western hemlock looper, Lambdina fiscellaria lugubrosa Hulst, periodically occur in stands of western hemlock, Tsuga heterophylla (Raf.) Sarg., along the coasts of British Columbia, Washington, and Oregon.