Occurrence and Correlations of Monoterpene Hydrocarbon Enantiomers in Pinus sylvestris and Picea abies

The relative amounts and enantiomeric compositions of monoterpene hydrocarbons in branch and trunk xylem, in needles, and in resin from apical buds in 18 Pinus sylvestris trees have been determined and compared with the terpene content in branch xylem and needles of Picea abies. Besides the high amount of (+)-3-carene, an excess of (+)--pinene has been found in P. sylvestris, whereas in P. abies (–)--pinene dominates over (+)--pinene. In P. sylvestris, clear positive correlations were found between (+)--pinene and (+)-camphene in the four tissues analyzed. Good positive correlations were also observed between (–)--pinene and (–)-camphene in the two types of xylem, between (+)--pinene and (+)--pinene in the resin, and between tricyclene and (–)-camphene in resin and needles. In P. abies, positive correlations were found between (+)--pinene and (+)-camphene in the branch xylem and between tricyclene and (–)-camphene as well as between (–)--pinene and (–)-camphene in the needles. Complex relationships between (–)--pinene and (–)--pinene were found both in the P. abies and in the P. sylvestris tissues. The importance of the enantiomeric composition of -pinene for the host selection of Ips typographus, Tomicus piniperda, and Hylobius abietis is discussed.     

Toxicity of allelopathic monoterpene suspensions on yeast dependence on droplet size

The toxic effects of the allelopathic nonsubstituted monoterpenes -pinene and limonene on yeast,Saccharomyces cerevisiae, were proportional to the size of the monoterpene droplets in suspension. Both the toxic effects and the size of the droplets in suspension were decreased by adding different solvents with the monoterpene as follows: dimethylsulfoxide – dimethylformamide ethanol > dioxane. Oxygen consumption was inhibited about 80% by 1 mM -pinene added in dimethylsulfoxide but less than 10% when -pinene was added in dioxane. Parallel decreases in droplet size and toxic effects of either monoterpene were also induced by hydrating the monoterpene-dimethylformamide or monoterpene-dimethylsulfoxide before addition to yeast. Molecular aggregation may be a mechanism to potentiate the allelopathic properties of monoterpenes when these associate with diverse soil components.     

Dose and enantiospecific responses of white pine cone beetles,Conophthorus coniperda,to alpha-Pinene in an eastern white pine seed orchard

The white pine cone beetle, Conophthorus coniperda, exhibited dose and enantiospecific responses to -pinene in stands of mature eastern white pine, Pinus strobus, in a seed orchard near Murphy, North Carolina, USA. (–)--Pinene significantly increased catches of cone beetles to traps baited with (± )-trans-pityol. (+)--Pinene did not increase catches of beetles to pityol-baited traps and interrupted the response of beetles to traps baited with (±)-trans-pityol and (–)--pinene. Maximal attraction of cone beetles to pityol-baited traps was obtained with lures releasing (–)--pinene at a rate of 103 mg/day at 23^°C. Lures releasing (–)--pinene at rates lower or higher than 103 mg/day resulted in reduced catches to traps baited with (±)-trans-pityol. The sex ratio in all catches was heavily male biased. Attraction of the clerid predator, Thanasimus dubius, to traps baited with (±)-trans-pityol increased significantly with the presence of -pinene, irrespective of enantiomeric composition. Maximal attraction of T. dubius to pityol-baited traps occurred with devices releasing (–)--pinene at the highest rate tested, 579 mg/d at 23^°C, a sub optimal rate for cone beetles.     

Response of Parasitoids Dendrosoter protuberans and Cheiropachus quadrum to Attractants of Phloeotribus scarabaeoides in an Olfactometer

The braconid Dendrosoter protuberans and the pteromalid Cheiropachus quadrum are two parasitoids of the olive bark beetle, Phloeotribus scarabaeoides. Several chemicals such as -pinene, -pinene, 2-decanone, 2-nonanone, decanal, undecanal, and n-butyl acetate have been identified as attractants in the laboratory for this scolytid. Under red light at 27°C in a laboratory olfactometer both parasitoids oriented positively to both enantiomers of -pinene, and females also responded to 2-decanone. Significant responses did not occur under white light or at lower temperatures. These results suggest that -pinene and 2-decanone could be involved in the location of P. scarabaeoides by its parasitoids. Consequently an attracticidal control tactic for this scolytid that included these chemicals could eliminate part of the parasitoid population. In an integrated pest management program, this problem should be considered.     

Volatile Production by Buds and Corollas of Two Sympatric, Confamilial Plants, Ipomopsis aggregata and Polemonium foliosissimum

We used solid-phase microextraction of headspace samples followed by gas chromatography and mass spectrometry to identify and quantify the major volatile compounds produced by the buds and corollas of Ipomopsis aggregata (Polemoniaceae), and we compared them to a sympatric, confamilial plant species, Polemonium foliosissimum. The two species have distinct floral morphologies and pollinators, but share a common predispersal seed predator that oviposits under the calyces of buds. Ipomopsis aggregata buds emitted fewer compounds than the corollas. The buds of I. aggregata were dominated by -pinene and, to a lesser extent, -pinene. The corollas of I. aggregata emitted a mixture of 10 compounds. Like the buds, I. aggregata corollas produced relatively high concentrations of -pinene as well as caryophyllene. In addition, the emission of four terpenoids, three esters, and one ketone added to the volatile bouquet of the corollas. Polemonium foliosissimum buds also emitted fewer compounds than the corollas. The buds of P. foliosissimum were dominated by -pinene and, to a lesser extent, -pinene. The corollas of P. foliosissimum were also dominated by -pinene along with three terpenoids, three alcohols, one ester, and two aldehydes. Comparing I. aggregata and P. foliosissimum, bud samples from both species produced considerable amounts of - and -pinene. Ipomopsis aggregata emitted more -pinene than -pinene, while P. foliosissimum emitted more -pinene. The corollas of the two species, however, differed in their volatile bouquet. The partition of volatiles between I. aggregata and P. foliosissimum buds and corollas and differences in volatile production between I. aggregata and P. foliosissimum are consistent with selection pressures exerted by organisms interacting with these plants.     

Enantiomeric Composition of Monoterpene Hydrocarbons in Some Conifers and Receptor Neuron Discrimination of α-Pinene and Limonene Enantiomers in the Pine Weevil, Hylobius abietis

The enantiomeric composition of seven monoterpene hydrocarbons in headspace volatiles of spruce sawdust and seedlings (Picea abies), pine seedlings (Pinus sylvestris), and branches of juniper (Juniperus communis) was determined by gas chromatographic separation on a -Cyclodextrin column. For the six monoterpenes, -pinene, camphene, -pinene, sabinene, limonene, and -phellandrene, both enantiomers were present, whereas for 3-carene only the (+)-configuration was found. The amount of each enantiomer varied considerably both in relation to total amount of all of them, and for the six pairs also in relation to the opposite enantiomer. One olfactory receptor neuron in the pine weevil (Hylobius abietis) showed a strong response to -pinene when stimulated with all four headspace materials via a GC equipped with a DB-WAX column. The same neuron was subsequently tested with repeated stimulations via the GC effluent containing the (+)- or (–)-enantiomer. A marked better response to (+)- than to (–)--pinene was elicited. Another olfactory receptor neuron that responded strongly to limonene when stimulated with the spruce volatiles was tested for enantiomers of limonene. This neuron responded more strongly to (–)- than to (+)-limonene, when stimulated alternately with each of the limonene enantiomers. Discrimination between enantiomers by plant olfactory receptor neurons suggests that the enantiomeric ratios of volatile compounds may be important in host location by the pine weevil.     

Chiral specificity in responses by the bark beetleDendroctonus valens to host kairomones

The attraction of the red turpentine beetle,Dendroctonus valens, to the resin volatiles of its host,Pinus ponderosa, is elicited by three chiral monoterpenes. In field assays response was greatest to (S)-(–)--pinene; 92% (S)-(–)--pinene found inP ponderosa resin was not attractive. However, 75% (R)-(+)--pinene, which occurs inPinus lambertiana, a sympatric host ofD. valens, was attractive. (S)-(–)--Pinene interrupted response to (R)-(+)--pinene. (S)-(+)-3-Carene from both hosts was attractive at the (R)-(+)--pinene level. Three sympatric coniferous nonhosts each have the same attractive monoterpenes but produce less resin. These studies demonstrate the importance of chirality of host compounds in the host finding behavior of this bark beetle.     

Chemical nature of larval osmeterial secretions of papilionid butterflies in the generaParnassius,Sericinus andPachliopta

Volatile components of the larval osmeterial secretion ofParnassius glacialis (Parnassiinae, Parnassiini) consisted of isobutyric acid, 2-methylbutyric acid, and their methyl esters. In contrast, the osmeterial exudate ofSericinus montela (Parnassiinae, Zerynthiini) was characterized as monoterpene hydrocarbons comprising-myrcene (Major),-pinene, sabinene, limonene, and-phellandrene, whereas that ofPachliopta aristolochiae (Papilioninae, Troidini) was composed of numerous sesquiterpene hydrocarbons, including-himachalene,-amorphene, and germacrene-A, and a few oxygenated sesquiterpenoids. In these three species, the chemical nature of the secretions of the last and the penultimate instars was essentially of similar quality, suggesting that the three genera,Parnassius, Sericinus, andPachliopta, are assigned to homogeneous types.     

Electroantennogram responses by mountain pine beetles,Dendroctonus ponderosae Hopkins,exposed to selected semiochemicals

Electroantennograms (EAGs) were obtained forD. ponderosae to the bark beetle pheromonestrans-verbenol,cis-verbenol,exo-brevicomin,endo-brevicomin, frontalin, verbenone; to the kairomones, -pinene, -pinene, camphene, -3-carene, limonene, myrcene; to a blend (111) oftrans-verbenol,exo-brevicomin, and myrcene; and to diacetone-alcohol. Male and female responses, in general, did not differ significantly over the whole EAG dose-response curves but differed at a few concentrations on many of the curves. There were more differences noted for pheromones than kairomones. The blend yielded among the largest EAGs in both sexes and appeared to show synergism. Responses of females were lower than those for males in most instances. Significant differences in responses by the two sexes were much fewer for the kairomones than the pheromones. EAG recovery rates tested at only one concentration showed significant differences between males and females for three pheromones,trans-verbenol,cis-verbenol, and verbenone, and two kairomones, camphene and -3-carene. Thresholds were quite low for most of the odorants exceptcis-verbenol, camphene, verbenone, and diacetone-alcohol in females, andcis-verbenol, verbenone, -pinene, and diacetone-alcohol in males. The results, using at least one EAG parameter, support behavioral and field studies involvingexo-brevicomin,trans-verbenol, frontalin, and the blend.     

Electroantennographic and coupled gas chromatographic-electroantennographic responses of the mediterranean fruit fly,Ceratitis capitata,to male-produced volatiles and mango odor

We have identified five compounds from the headspace of calling male Mediterranean fruit flies (medfly),Ceratitis capitata (Wiedemann), and three compounds from the headspace of ripe mango (Mangifera indica L). using coupled gas chromatographic-electroantennographic (GC-EAG) recordings, coupled gas chromatographic-mass spectrometric (GC-MS) analysis, and electroantennographic (EAG) assays of standards. The male-produced volatiles eliciting responses from female antennae were ethyl-(E)-3-octenoate, geranyl acetate, (E,E)--farnesene, linalool, and indole. An EAG dose-response test of linalool enantiomers and indole with female medfly antennae showed relatively strong EAG activities, but no significant difference between (R)-(-)-linalool and (S)-(+)-linalool. The three mango volatiles were identified as (1S)-(-)--pinene, ethyl octanoate, and-caryophyllene. In addition, a strong antennal response was recorded from a contaminant,-copaene, present in a commercial sample of-caryophyllene. The EAG response amplitudes from both male and female antennae to the above three mango volatiles were significantly greater than to a hexanol control. For both male and female medfly antennae, the greatest EAG responses were elicited by-caryophyllene followed by ethyl octanoate. The mean EAG responses of female antennae to-caryophyllene and (1S)-(-)--pinene were significantly greater than those of male antennae.     

Opposing Effects of Host Monoterpenes on Responses by Two Sympatric Species of Bark Beetles to Their Aggregation Pheromones

The effects of host tree monoterpenes on primary and secondary attraction of the bark beetles, Ips pini and Ips grandicollis, and their associated phloeophagous insects were investigated. Monoterpenes alone were not attractive to I. pini. However, monoterpenes mediated the attraction of I. pini to its aggregation pheromones. With the exception of 3–carene, the effect of monoterpenes on I. pini's response to its pheromone, ipsdienol plus lanierone, was inhibitory. In contrast, (–)--pinene both attracted I. grandicollis and enhanced the attraction of I. grandicollis to its pheromone, ipsenol. No monoterpene inhibited the response of I. grandicollis to its pheromone. The inhibitory effect of host monoterpenes on I. pini response to its aggregation pheromone differs from previous work, in which monoterpenes either synergized responses or had no effect. In addition to possible geographic differences, the concentrations used in our study simulated trees that had begun to respond to attack, whereas previous studies deployed lower concentrations, which simulated constitutive phloem from unattacked trees. These results support the view that trees that undergo induced responses to bark beetles sometimes inhibit attraction of additional beetles, despite the beetles' production of aggregation pheromones. Neither species displayed cross-attraction to the pheromone of the other. The red turpentine beetle, Dendroctonus valens, showed weak and consistent attraction to (+)--pinene and in some cases to (–)--pinene. Attraction to (–)--pinene was usually enhanced by Ips spp. pheromones. The absence of strong attraction to (+)--pinene and partial attraction to (–)--pinene suggest that the effects of different stereoisomers of -pinene on D. valens vary throughout its geographical range. Hylastes porculus was also attracted to some monoterpenes, particularly (–)--pinene. An additional 10 species of phloeophagous insects were caught in response to monoterpenes and/or pheromones, including the pine root weevils, Hylobius pales and Pachylobius picivorus, and the longhorned beetle, Monochamus carolinensis.     

Oxygenated monoterpenes produced by yeasts,isolated fromIps typographus (Coleoptera: Scolytidae) and grown in phloem medium

When yeasts associated withIps typographus beetles were grown in an aqueous phloem medium for two days, the main oxygenated monoterpenes produced were -terpineol and borneol. Terpinene-4-ol, myrtenol, andtrans-pinocarveol were also found but in lesser amounts. Of the six strains used in this study,Hansenula capsulata andCandida nitratophila produced the largest amounts of oxygenated monoterpenes. Addition of -pinene to the phloem medium generally reduced the amounts of oxygenated monoterpenes, probably because this substance is toxic to all tested yeast species. OurCandida diddensii strain seemed to be particularly sensitive to -pinene. None of the yeast strains producedcis-verbenol,trans-verbenol, or verbenone from the medium or from added -pinene.This study was made within the project Odour Signals for Control of Pest Insects.     

Measurement of monoterpene hydrocarbon levels in vapor phase surrounding single-leaf pinyon (Pinus monophylla Torr. & Frem.: Pinaceae) understory litter

A headspace air-sampling experiment was performed in the laboratory to determine the identity and concentrations of monoterpene hydrocarbons that could be attained in the vapor phase surrounding single-leaf pinyon pine (Pinus monophylla Torr. & Frem.) understory litter using controlled air collection conditions at a simulated field temperature of 37.8°C. The total monoterpene hydrocarbon content in 21 sequential samples of air collected from a sealed glass carboy packed with 1.44 kg of single-leaf pinyon litter equivalent to a bulk density of 0.15 g/cm³ averaged 3.56 ± 1.04 mg/liter. The monoterpenes-pinene and camphene were present in the vapor phase at the highest concentrations, averaging 2.40±0.64 and 0.68±0.22 mg/ liter, respectively. Myrcene,-pinene, 3-carene,-phellandrene, and-terpinene were all present at average concentrations below 0.30 mg/liter. The first two traps of the sequential air samples yielded the highest concentrations for the monoterpene hydrocarbons; however, the average total levels were relatively stable throughout the remaining 19 traps. Therefore, the data indicate that these hydrocarbons volatilize from the source pinyon litter and maintain an equilibrium in the vapor phase. Although this analysis was conducted using an artificial system, combined with results from our previous studies, mounting evidence indicates that monoterpene hydrocarbons present in the vapor phase of the single-leaf pinyon understory may be toxic to a variety of native plant species and thus further implicates allelopathy as a significant contributor to the observed patterning of associated vegetation in these forests.     

Effects of biotic and abiotic stress on induced accumulation of terpenes and phenolics in red pines inoculated with bark beetle-vectored fungus

This study characterized the chemical response of healthy red pine to artificial inoculation with the bark beetle-vectored fungusLeptographium terebrantis. In addition, we sought to determine whether stress altered this induced response and to understand the implications of these interactions to the study of decline diseases. Twenty-five-year-old trees responded to mechanical wounding or inoculation withL. terebrantis by producing resinous reaction lesions in the phloem. Aseptically wounded and wound-inoculated phloem contained higher concentrations of phenolics than did constitutive tissue. Trees inoculated withL. terebrantis also contained higher concentrations of six monoterpenes,-pinene,-pinene, 3-carene, limonene, camphene, and myrcene, and higher total monoterpenes than did trees that were mechanically wounded or left unwounded. Concentrations of these monoterpenes increased with time after inoculation. Total phenolic concentrations in unwounded stem tissue did not differ between healthy and root-diseased trees. Likewise, constitutive monoterpene concentrations in stem phloem were similar between healthy and root-diseased trees. However, when stem phloem tissue was challenged with fungal inoculations, reaction tissue from root-diseased trees contained lower concentrations of-pinene, the predominant monoterpene in red pine, than did reaction tissue from healthy trees. Seedlings stressed by exposure to low light levels exhibited less extensive induced chemical changes when challenge inoculated withL. terebrantis than did seedlings growing under higher light. Stem phloem tissue in these seedlings contained lower concentrations of-pinene than did nonstressed seedlings also challenge inoculated withL. terebrantis. It is hypothesized that monoterpenes and phenolics play a role in the defensive response of red pine against insect-fungal attack, that stress may predispose red pine to attack by insect-fungal complexes, and that such interactions are involved in red pine decline disease. Implications to plant defense theory and interactions among multiple stress agents in forest decline are discussed.To whom correspondence should be addressed at USDA Forest Service, 2500 Shreveport Hwy., Pineville, Louisiana 71360.     

Monoterpene effect on feeding choice by deer

A previous study showed that Sitka black-tailed deer (Odocoileus hemionus sitkensis) consumption was negatively correlated with monoterpene content in western redcedar (Thuja plicata). To test whether these monoterpenes were deterrent to Sitka black-tailed deer, we performed feeding choice experiments with four hydrocarbon (sabinene, myrcene, -pinene, and d + l-limonene) and one oxygenated (,-thujone) monoterpene solution at their highest natural concentration in western redcedar foliage. To test whether deer response was species specific, we ran similar experiments on European roe deer (Capreolus capreolus) and rusa deer (Cervus timorensis russa). In all experiments, monoterpenes were repellent. Solutions with ,-thujone, the major monoterpene in redcedar leaves, were the most repellent of the solutions tested. We then analyzed how black-tailed and roe deer responded to (1) an increase in concentration of the monoterpenes with the weakest repellent effects (hydrocarbon monoterpenes) and (2) a decrease in concentration of the monoterpene with strongest effect (,-thujone). Repellency tended to increase with concentration for hydrocarbon monoterpenes, but remained strong for ,-thujone. As wild deer regularly feed on plants containing monoterpenes, this raises the question as to how the animals deal with these molecules.     

Interspecific variation in terpenoid composition of defensive secretions of European Reticulitermes termites

Sixteen terpene compounds were isolated from the soldier defensive secretions of seven European termite taxa of the genus Reticulitermes (Isoptera, Rhinotermitidae). We describe species-specific mixtures of monoterpenes (-pinene, -pinene, limonene), sesquiterpenes (germacrene C, germacrene A, germacrene B, -selinene, -selinene, -selinene, (E)--farnesene, -cadinene, nerolidol), diterpenes (geranyl linalool, geranyl geraniol, geranyl geranial), and one sesterterpene (geranyl farnesol). Compounds were purified by HPLC and their structures determined by means of MS spectrometry, or 1D and 2D NMR spectroscopy. Comparison of two different analytical approaches, GC-MS and HPLC with subsequent NMR spectroscopy, revealed Cope rearrangement of germacrene A, germacrene B, and germacrene C to the respective -elemene, -elemene, and -elemene under GC conditions, thus demonstrating the limits for this analytical approach. The species-specific compound composition provides insight into taxonomy and species origin of European Reticulitermes. The biological significance of the species-specific composition of Reticulitermes defensive secretions is briefly discussed.     

Correspondence of soldier defense secretion mixtures with cuticular hydrocarbon phenotypes for chemotaxonomy of the termite genus Reticulitermes in North America

Soldier defense secretions from samples of Reticulitermes collected in California, Nevada, Arizona, New Mexico, and Georgia were characterized and correlated with cuticular hydrocarbon phenotypes. Twenty-seven cuticular hydrocarbon phenotypes have been defined, and soldier defense secretion (SDS) phenotypes have been described for 25 of these. Forty-five terpenoid compounds were found, including monoterpenes, sesquiterpenes, and a few diterpenes. The monoterpenes include (–)--pinene, (–)--pinene, (–)-camphene, myrcene, (Z)- and (E)-ocimene, and (–)-limonene. The major sesquiterpenes produced are (+)--cadinene, (+)--cadinene aldehyde, (–)-germacrene A, germacrene B, -himachalene, and -bisabolene. Some SDS phenotypes pair with more than one cuticular hydrocarbon phenotype; however, with two exceptions, each hydrocarbon phenotype is associated with only one SDS phenotype. These chemical characterizations lend support to the conclusion that there are numerous undescribed species of Reticulitermes in North America.     

Technique for using microencapsulated terpenes in lepidopteran artificial diets

We have developed and tested a technique to microencapsulate terpene compounds by forming gelatin-walled microcapsules around the terpene essential oils. Eight terpenes that are common constituents of Douglas fir (Pseudotsuga menziesii) oleoresin were encapsulated, including five monoterpenes (-pinene,-pinene, camphene, myrcene, and limonene) and three oxygenated monoterpenes (bornyl acetate, linalool, and-citronellol). The encapsulated terpenes were mixed into artificial diets to determine the effects they had on western spruce budworm (Choristoneura occidentalis) survival and reproduction, using a three-generation bioassay. We describe the technique and present data from preliminary bioassays with seven of the terpenes to demonstrate thatC. occidentalis larvae would consume diets fortified with microencapsulated terpenes. The technique is useful because it helps to reduce the rate at which terpenes volatilize from the diets and it packages the terpenes in a manner more closely resembling the way they are present in the resin canals of plant foliage. Many scientists investigating the biological importance of terpenes in mediating plant-herbivore interactions may find that microencapsulated terpenes are useful in both laboratory diet studies and field and greenhouse experiments with plant material.     

Limonene inhibits attraction to α-pinene in the pine weevilsHylobius abietis andH. pinastri

The field responses ofHylobius abietis (L.) andH. pinastri (Gyllenhal) (Coleoptera: Curculionidae) to various combinations of two host monoterpenes and ethanol were studied using baited pitfall traps. Both species were attracted to -pinene, and when ethanol was added the attraction increased by 5–16 times. Limonene completely inhibited the attraction to -pinene, even when the release rate of limonene was only about 1/50 that of -pinene. The catches in traps with -pinene and limonene as well as with limonene alone were similar in size to catches in empty control traps, i.e., no true repellent effect was demonstrated. When limonene was added to the combination of -pinene and ethanol on old clear-cuttings, the catch ofH. pinastri was completely inhibited while that ofH. abietis was reduced by two thirds. On fresh clear-cuttings the inhibitory effect of limonene on the attraction to the -pinene-ethanol combination was small or absent. Some aspects of host interactions are discussed as are practical implications regarding the choice of seedling material for planting and prospects of finding deterrents for protecting seedlings from pine weevil damage.     

Field responses of certain forest Coleoptera to conifer monoterpenes and ethanol

Field experiments using baited sticky stovepipe traps and Lindgren multiple funnel traps were done near Chalk River, Ontario, Canada, to determine the effects of conifer monoterpenes (-pinene, -pinene, myrcene, limonene, camphene and carene) and ethanol on the number of beetles captured. Several species of conifer-feeding beetles were attracted to the monoterpenes or to monoterpenes and ethanol, including species in the families Cerambycidae (Asemum striatum, Acmaeops proteus, Xylotrechus undulatus, Monochamus scutellatus), Curculionidae (Pissodes strobi, Hylobius pales), and Scolytidae (Dryocetes autographus, Ips grandicollis). Species of Buprestidae generally did not respond to the monoterpenes or to ethanol. Species of Cleridae (Thanasimus dubius, Enoclerus nigripes rufiventris, Enoclerus nigrifrons gerhardi) which are predators of conifer bark beetles were attracted to the monoterpenes. Synergism between monoterpenes and ethanol was evident forM. scutellatus, H. pales, andD. autographus. While -pinene was the most potent attractant for most beetle species, monoterpenes other than -pinene synergized attraction to ethanol forD. autographus. Attraction of beetles to commercial turpentine and ethanol did not differ significantly from attraction to a pure monoterpene blend and ethanol.