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AbstractIn British Columbia, native willows (Salixspp.) (Salicaceae) and, to a lesser extent, black cottonwood (Populus trichocarpaTorr. & Gray) (Salicaceae) are frequently attacked by the poplar and willow borer, Cryptorhynchus lapathi(L.) (Coleoptera: Curculionidae). Red alder (Alnus rubraBong.) (Betulaceae), trembling aspen (Populus tremuloidesMichx.), and bigleaf maple (Acer macrophyllumPursh) (Aceraceae) are not attacked. We studied olfaction and feeding preferences in the laboratory and feeding, oviposition, and emergence in the field. Female C. lapathipreferred Scouler's willow (Salix scoulerianaBarratt exHook.) over all other species by olfaction, but males did not discriminate between Scouler's willow and black cottonwood or trembling aspen. All species elicited at least some attraction in no-choice situations. Willow was generally preferred for feeding, but black cottonwood and red alder were also acceptable, unlike trembling aspen or bigleaf maple. In field caging experiments, adult weevils emerged from willow, black cottonwood, and red alder. We conclude that olfaction and feeding preferences are sufficiently powerful to mediate the frequent attack observed on native willows, the intermediate levels of attack on cottonwood, and the absence of attack on red alder. Successful development on red alder suggests that C. lapathicould expand its host range to include this species.

Summary. Nine compounds identified from captured volatiles of the Douglas-fir beetle, Dendroctonus pseudotsugae, the mountain pine beetle, D. ponderosae, and the spruce beetle, D. rufipennis, that elicited antennal responses in males and females of one or more of these species were tested in the field to determine behavioural activity. 1-Octen-3-ol, found in the volatiles of females of all three species decreased the response of male and female coastal and male interior D. pseudotsugae and both sexes of D. ponderosae to their aggregation pheromones. Acetophenone, identified in the volatiles of females of all three species, significantly decreased the response of interior female D. pseudotsugae. trans-Verbenol, a potent aggregation pheromone of D. ponderosae, decreased the response of both sexes of D. pseudotsugae, while 3-methyl-2-cyclohexen-1- one (MCH), the antiaggregation pheromone of D. pseudotsugae and D. rufipennis decreased the response of both sexes of D. ponderosae. While it has been demonstrated that semiochemical mediated interspecific communication occurs among bark beetles infesting the same host, this study demonstrates that beetles can perceive signals emitted by heterospecifics attacking nonhosts and can potentially use them to avoid attacking the wrong species of conifer.

AbstractThe poplar and willow borer, Cryptorhynchus lapathi(L.), known to be present in British Columbia since 1923, primarily attacks species of SalixL. (Salicaceae) and PopulusL. (Salicaceae). Larvae bore into stems, causing them to break easily. The impact of the weevil has been rising in recent years because of the increasing importance of poplar and willow from both economic and ecological perspectives. We conducted a study at 45 locations in British Columbia to determine host use among native Salixspp. and the between- and within-tree dynamics of C. lapathi. There were 11 new host records, but the incidence of attack was similar among species. Attacked trees were larger in general and had more dead wood and stems, more adventitious branches per stem, more total breaks per stem, and more naturally caused breaks per stem than their attack-free neighbours. Breaks caused by C. lapathitended to be slightly larger in diameter and lower on the stem than naturally caused breaks. Bases of stems were preferentially attacked, and C. lapathiselected large stems in which to oviposit. As large attack-free trees become less abundant, weevils apparently start to attack small-diameter stems. Although C. lapathiis adversely affecting the health of willows in British Columbia, there is no evidence that any Salixspecies is threatened by weevil-caused extinction.

Summary.: The mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine engraver, Ips pini (Say), often co-exist in lodgepole pine, Pinus contorta var. latifolia Engelmann. Intra- and interspecific semiochemical communication occurs in both species and their complete semiochemical repertoire and precise dynamics of pheromone production have not been elucidated. Porapak-Q extracts of captured volatiles from beetles of each species aerated at different attack phases (freshly emerged, pioneer sex alone in the log and both sexes paired in new galleries), followed by gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectroscopic analyses identified 17 compounds (seven compounds common to both species, six present in D. ponderosae and four present in I. pini) that excited the antennae of either or both species. Seven compounds for D. ponderosae and nine for I. pini had not been assessed for behavioural activity. In field trapping experiments, 2-phenylethanol produced by both species inhibited the response of D. ponderosae to its aggregation pheromones. exo- and endo-Brevicomin produced by D. ponderosae significantly decreased the response of I. pini to its aggregation pheromone ipsdienol. Nonanal, a ubiquitous compound found in the volatiles of lodgepole pine, various nonhosts and in both beetle species deterred the response of I. pini to ipsdienol. The occurrence of cis-verbenol, trans-verbenol and verbenone in emergent I. pini, and verbenone and 2-phenylethanol in emergent D. ponderosae suggests that these compounds may inhibit aggregation and induce dispersal following emergence. Termination of aggregation in D. ponderosae appears to depend on the production of frontalin in combination with changes in the relative ratios of verbenone, exo-brevicomin, trans-verbenol and 2-phenylethanol. In I. pini, the cessation of ipsdienol production by males is probably the main factor in terminating aggregation.

Summary.: Using Porapak Q traps, we collected the bark volatiles of six angiosperm trees native to British Columbia: black cottonwood, Populus trichocarpa Torr. & A. Gray (Salicaceae), trembling aspen, P. tremuloides Michx. (Salicaceae), paper birch, Betula papyrifera Marsh. (Betulaceae), bigleaf maple, Acer macrophyllum Pursh (Aceraceae), red alder, Alnus rubra Bong. (Betulaceae), and Sitka alder, A. viridis ssp. sinuata (Regel) Á. Löve & D. Löve (Betulaceae). Utilising coupled gas chromatographic-electroantennographic detection analysis, the captured volatiles were assayed for antennal responses in five species of coniferophagous bark beetles (Coleoptera: Scolytidae), sympatric with most or all of the angiosperm trees: the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, the mountain pine beetle, D. ponderosae Hopkins, the spruce beetle, D. rufipennis (Kirby), the western balsam bark beetle, Dryocoetes confusus Swaine, and the pine engraver, Ips pini (Say). The identities of 25 antennally-active compounds were determined by coupled gas chromatographic-mass spectroscopic analysis, and co-chromatographic comparisons with authentic chemicals. The compounds identified were: hexanal, (E)-2-hexenal, (Z)-3-hexen-1-ol, 1-hexanol, heptanal, α-pinene, frontalin, benzaldehyde, β-pinene, 2-hydroxycyclohexanone, 3-carene, limonene, β-phellandrene, benzyl alcohol, (E)-ocimene, salicylaldehyde, conophthorin, guaiacol, nonanal, methyl salicylate, 4-allylanisole, decanal, thymol methyl ether, (E)-nerolidol, and dendrolasin. A number of these compounds are known semiochemicals that are active in the behaviour of other organisms, including bark beetles, suggesting a high degree of semiochemical parsimony. Antennally-active compounds ranged from seven in A. viridis to 17 in P. trichocarpa. The fewest number of compounds (9) were detected by I. pini and the largest number (24) were detected by D. pseudotsugae. Six compounds excited the antennae of all five species of bark beetles. The large number of antennally-active compounds detected in common by numerous bark beetles and present in common in numerous nonhost trees supports the hypothesis of olfaction-based recognition and avoidance of nonhost angiosperm trees during the process of host selection by coniferophagous bark beetles.

AbstractIn laboratory experiments adults and nymphs of the western conifer seed bug, Leptoglossus occidentalisHeidemann, were allowed to feed on mature seeds of Douglas-fir, Pseudotsuga menziesii(Mirbel) Franco. Weight-loss measurements and scanning electron microscopy provided strong supporting evidence for the use of simple radiographic diagnosis as a method of classifying feeding damage to seeds into four categories: light (greater than two thirds of seed contents remaining), moderate (one third to two thirds of seed contents remaining), severe (less than one third of seed contents remaining), and extreme (seed empty). Scanning electron micrographs showed the apparent depletion of lipid and protein storage reserves which was verified by quantitative analyses that showed significant loss of lipid and buffer-insoluble (crystalloid) storage protein from seeds in all damage categories. The amount of buffer-soluble (matrix) protein was reduced in seeds from the severe and extreme damage categories. The increase in buffer-soluble protein observed in lightly damaged seeds was likely due to the solubilization of crystalloid storage protein, as a result of its breakdown into smaller peptides. Our results suggest that through the action of both lipases and proteases, L. occidentaliscan have a serious impact on the major storage reserves of conifer seeds. Moreover, our data suggest that L. occidentalisfeeds in a different manner than the laceration and flushing method found in other seed-feeding Hemiptera.

Summary.: Male obliquebanded leafrollers, Choristoneura rosaceana (Harris), were induced to respond to a pheromone source tainted with a behavioural antagonist, Z9-tetradecenyl acetate, when a source releasing the antagonist was placed 10 cm upwind of the tainted source in a wind tunnel. However, placement of the antagonist upwind of an attractive pheromone source did not interrupt pheromone-mediated responses. Placement of a source releasing Z9-tetradecenyl acetate, a minor pheromone component of the sympatric species, the threelined leafroller, Pandemis limitata (Robinson), upwind of a calling P. limitata female, reduced conspecific male pheromone-mediated response but resulted in upwind flight by male C. rosaceana and contact with heterospecific females. Male P. limitata locked on and flew upwind to but did not contact heterospecific females when a source releasing Z9-tetradecenyl acetate was positioned upwind of a calling C. rosaceana female. In the field, adaptation or habituation to Z9-tetradecenyl acetate caused by atmospheric treatment with this compound apparently resulted in reciprocal heterospecific pheromone responses. More C. rosaceana males were captured in traps baited with their pheromone and the behavioural antagonist in small field plots treated atmospherically with Z9-tetradecenyl acetate than in nontreated control plots. Fewer male P. limitata were captured in traps baited with their own pheromone, or with C. rosaceana pheromone tainted with Z9-tetradecenyl acetate in plots treated atmospherically with Z9-tetradecenyl acetate than in nontreated control plots. We argue that Z9-tetradecenyl acetate is an important synomone which assists in partitioning the sexual chemical communication channels of C. rosaceana and P. limitata.

AbstractIn randomized complete block experiments using multiple-funnel traps frontalin was only moderately attractive to spruce beetles, Dendroctonus rufipennisKirby, in northern British Columbia. MCOL (1-methylcyclohex-2-en-1-ol) of any enantiomeric composition significantly enhanced the attraction of both sexes (up to 3.4 and 4.2 times for females and males, respectively) to traps baited with frontalin. The lack of an enantiospecific preference for MCOL aligns beetles in northern British Columbia with those in southeastern British Columbia and northern Alberta, but not with enantiospecific populations in southern British Columbia and Alaska. In tree baits, neither MCOL nor seudenol (3-methylcyclohex-2-en-1-ol) enhanced the efficacy of frontalin. The power of frontalin alone at a release rate of 1.2 mg per 24 h (half the rate in commercial baits) indicates that the currently used operational tree baits could be modified by lowering the dose and eliminating a-pinene.

AbstractAn extract from seeds of the neem tree, Azadirachta indicaA. Juss, enriched with azadirachtin, was evaluated in three experiments for control of the spruce aphid, Elatobium abietinum(Walker), on potted spruce trees in a greenhouse. The extract in Exps. 1 and 2 was first applied in February 1993 when spruce aphid populations were initially low; populations were observed weekly for 15 weeks. In Exp. 1, foliar applications to the runoff point of 150 ppm azadirachtin applied three times (biweekly) held populations below 5.3 aphids per 6-cm twig samples; populations on trees treated at 75 ppm, or with emulsifier only, reached 32.2 and 26.9 aphids per sample, respectively. With five weekly applications (Exp. 2), suppression to < 14 aphids per sample was achieved with both 150- and 75-ppm treatments; populations on control trees peaked at 36.8 aphids per sample. The extract at 150 ppm in Exp. 3 significantly reduced the number of aphids on trees that initially had high populations. The results indicate that neem has potential for operational use against aphids in conifer seed orchards.

AbstractLeptoglossus occidentalisHeidemann (Hemiptera: Coreidae) is considered to be an important cone and seed pest in seed orchards in British Columbia; however, no impact studies have been done in Canada. Surveys to determine the distribution of L. occidentaliswere conducted over a 3-year period in three coastal seed orchards of Douglas-fir, Pseudotsuga menziesii(Mirb.) Franco, and over a 2-year period in two seed orchards of lodgepole pine, Pinus contortavar. latifoliaEngelmann. Leptoglossus occidentaliswas found to distribute itself in patches, coinciding with a clonal preference. Seed losses were assessed for 2 years in the coastal Douglas-fir orchards and for 1 year in one lodgepole pine orchard. The percentages of partially filled seed that could have been caused by feeding of L. occidentalisor by a number of other factors were < 5% in coastal Douglas-fir for both 1992 and 1993 and ~14% in lodgepole pine in 1993. Apparently because populations of L. occidentaliswere low, there was no correlation between the percentage of partially filled seed and number of insects per tree. Except in unusual circumstances, management measures in Canada are judged not to be necessary as populations of L. occidentalisare consistently below the calculated threshold levels required to cause =5% loss in seed production.

AbstractFeeding preferences of the white pine weevil, Pissodes strobi(Peck), for resistant or susceptible Sitka spruce, Picea sitchensis(Bong) Carr., were investigated using three types of laboratory bioassay. In paired-twig bioassays, fall weevils were significantly deterred from feeding up to 80% by resistant clones from four British Columbia provenances: Green Timbers, Cedarvale, Haney, and Big Qualicum. Females showed greater discrimination than males. Spring weevils were deterred from feeding by clones from the Green Timbers and Big Qualicum provenances by up to 60%. Fall males were more consistently deterred than spring males, suggesting that some host selection occurs in the fall. Females were significantly deterred from ovipositing on twigs from one clone from Big Qualicum, and stimulated by clones from Cedarvale when given a choice. Given no choice, however, they were significantly deterred from ovipositing, but not feeding by several resistant clones. In agar-disc bioassays, spring weevils were significantly deterred from feeding by bark from the provenances of Cedarvale and Big Qualicum by up to 86%. Trees from the provenances of Big Qualicum and Green Timbers caused the most consistent feeding or oviposition deterrency and may rely on this in part as a resistance mechanism. Because not all resistant clones and provenances were deterrent, we hypothesize that these trees may employ other resistance mechanisms which could be incorporated along with feeding and oviposition deterrency into breeding for resistance.

AbstractThe pine engraver, Ips piniSay, and Pityogenes knechteliSwaine often co-exist in lodgepole pine, Pinus contoitavar. latifoliaEngelmann. We tested the hypotheses that P. knechteliproduces an attractive pheromone and that the attraction of P. knechteliand I. pintto conspecifics is inhibited by the presence of the other species. Pityogenes knechtelimales and females were attracted to bolts infested with conspecific males and to bolts infested with I. pinimales; however, there was no significant cross-attraction of I. pinimales or females to bolts infested with P. knechtelimales. Attraction of P. knechteliand I. pintmales and females to bolts infested with conspecific males was not inhibited in the presence of bolts infested with males of the other bark beetle species. Pityogenes knechtelihas no potential for competitive displacement of I. pinibut may enhance the adverse effect of I. pinion the mountain pine beetle, Dendroctonus ponderosaeHopkins.

AbstractThe response of the western balsam bark beetle, Dryocoetes confususSwaine, to subalpine firs, Abies lasiocarpa(Hook.) Nutt., baited with (±)-exo-brevicomin (EXOB) or 9:1 blends of EXOB and endo-brevicomin (ENDOB), in two chiral combinations: (+):(±) and (+):(+), was assessed in a heavily infested stand in British Columbia. Unbaited control trees were not attacked, and the proportion of mass-attacked baited trees was similar for all other treatments. However, trees baited with the (+):(+) blend had the highest number of attacks per square metre, and they were also surrounded by the most attacked trees. The (+):(±) blend was intermediate in attractancy, and (±)EXOB was the least attractive bait. Pheromone-based management of D. confususinfestations may be more effective with the 9:1 blend of (+)EXOB:(+)ENDOB than with the previously used (±)EXOB baits.

Male coconut rhinoceros beetles,Oryctes rhinoceros (L.), produce three sex-specific compounds, ethyl 4-methyloctanoate, ethyl 4-methylheptanoate, and 4-methyloctanoic acid, the first of which is an aggregation pheromone. Synthesis of these compounds involving conjugate addition of organocuprates to ethyl acrylate is reported. In field trapping experiments, (4S)-ethyl 4-methyloctanoate and the racemic mixture were equally attractive and 10 times more effective in attracting beetles than ethyl chrysanthemumate, a previously recommended attractant. Ethyl 4-methylheptanoate was as attractive as ethyl chrysanthemumate and more attractive than 4-methyloctanoic acid, but further studies are required before it can be classed as an aggregation pheromone. Compared to ethyl 4-methyloctanoate alone, combinations of the three male-produced compounds did not increase attraction, whereas addition of freshly rotting oil palm fruit bunches to pheromone-baited traps significantly enhanced attraction. With increasing dose, captures ofO. rhinoceros increased, but doses of 6, 9, and 18 mg/day were competitive with 30 mg/day lures. Newly designed vane traps were more effective in capturing beetles than were barrier or pitfall traps. Results of this study indicate that there is potential for using ethyl 4-methyloctanoate in operational programs to controlO. rhinoceros in oil palm plantations.

Female white pine cone beetles,Conophthorus coniperda, attacking second-year cones of eastern white pine,Pinus strobus L., produced a sex-specific pheromone that attracted conspecific males in laboratory bioassays and to field traps. Beetle response was enhanced by host monoterpenes. The female-produced compound was identified in volatiles collected on Porapak Q and in hindgut extracts as (+)-trans-pityol, (2R,5S)-(+)-2-(1-hydroxy-1-methylethyl)-5-methyltetrahydrofuran. Males and females produced and released the (E)-(-)-spiroacetal, (5S,7S)-(-)-7-methyl-1,6-dioxaspiro[4.5]decane, which was not an attractant for either sex, but acted as a repellent for males. Porapak Q-trapped volatiles from both sexes contained (+)-trans-pinocarveol and (-)-myrtenol. In addition, hindgut extracts of females containedtrans-verbenol, while males had pinocarvone and verbenone. Work in Georgia and Canada confirmed that the same isomers of pityol and spiroacetal are present in two distinct and widely separated populations ofC. coniperda.

Analyses of abdominal extracts and beetle-produced volatiles revealed that femaleConophthorus resinosae andC. banksianae produced optically pure (E)-(+)-pityol [(2R,5S)-(+)-2-(1-hydroxy-1-methylethyl)-5-methyltetrahydrofuran]. In field tests, traps baited with (E)-(±)- or (E)-(+)-pityol captured only males. Addition of host oils to traps baited with pityol did not significantly enhance the capture of males. Males of these former sibling species produced the spiroacetal (5S,7S)-(−)-7-methyl-1,6-dioxaspiro[4.5]decane with high optical purity (96%). Addition of the racemate or the optical isomers of the spiroacetal to traps baited with (E)-(±)-pityol almost completely inhibited the capture of males. It is hypothesized that to ensure their reproductive success, males produce the spiroacetal to repel rival males. Species specificity in pityol and the spiroacetal was not found betweenC. resinosae andC. banksianae, thus supporting their synonymy.

Production of 4-methyl-5-nonanol, and 4-methyl-5-nonanone by two sympatric Asian palm weevils,Rhynchophorus ferrugineus (Oliv.) andR. vulneratus (Panz.) suggested that enantiospecificity of either compound could impart species specificity of pheromone communication. Weevil-produced, racemic 4-methyl-5-nonanol and 4-methyl-5-nonanone and their stereoselectively synthesized optical isomers were subjected to gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometry (MS) on a chiral Cyclodex-B column. Only theS,S stereoisomer of 4-methyl-5-nonanol was EAD active and was produced by bothR. ferrugineus andR. vulneratus. Production and EAD activity of (S)-4-methyl-5-nonanone exceeded that of its antipode in both weevils. In field experiments in Java. (4S, 5S)-4-methyl-5-nonanol and the stereoisomeric mixture were equally attractive. The 4R,5R stereoisomer was inactive. The corresponding ketone enantiomers neither enhanced nor reduced attraction to (4S,5S)-4-methyl-5-nonanol. Lack of apparent differences betweenR. ferrugineus andR. vulneratus pheromones suggests that synonomy of both weevils should be considered unless other pre- or postzygotic reproductive isolating mechanisms are disclosed in future studies.

Ipsenol was identified from the frass of male, but not female,Ips latidens from British Columbia, feeding in phloem tissue of lodgepole pine,Pinus contorta var.latifolia. The responses ofJ. latidens to sources of ips-enol andcis-verbenol were determined with multiple-funnel traps in stands of lodgepole pine in British Columbia. Ipsenol attracted both male and femaleI. latidens, verifying that it is a pheromone for this species. MaleI. latidens showed a slight preference for (S)-(-)-ipsenol.cis-Verbenol was not produced by beetles of either sex and, in contrast to an earlier report, both enantiomers inhibited attraction to ipsenol-baited traps. The predators,Enoclerus sphegeus andThanasimus undatulus (Cleridae), were attracted to traps baited withcis-verbenol and ipsenol.

The first known sex pheromone for the family Miridae is reported for the mullein bug,Campylomma verbasci (Meyer) (Heteroptera: Miridae). Extracts of and Porapak Q-trapped volatiles from females were attractive to males in field bioassays. Butyl butyrate and hexyl butyrate were the predominant compounds in the females' volatiles, but these compounds previously had been found to be inactive when released alone or in combination. Butyl butyrate in combination with an isolated trace chemical, (E)-crotyl butyrate (which was inactive alone), rivaled the attraction elicited by five live females. When synthetic butyl butyrate and (E)-crotyl butyrate in a 16: 1 ratio were released at 91 or 183 µg/day, they comprised an effective attractant for male bugs.

The responses ofIps pini (Scolytidae) to multiple-funnel traps baited with the pheromone, ipsdienol, and various monoterpenes were determined in stands of lodgepole pine in southern and central British Columbia.Ips pini was attracted to both ipsdienol and ß-phellandrene, demonstrating that ß-phellandrene is a kairomone for this species.Lasconotus complex (Colydiidae) and aCorticeus sp. (Tenebrionidae) were attracted to both ipsdienol and ß-phellandrene. TheCorticeus sp. exhibited a synergistic response to the combination of ipsdienol and ß-phellandrene; the responses of the other two species to the combination were additive. The predators,Thanasimus undatulus, Enoclerus sphegeus, andE. lecontei (Cleridae), were attracted to ipsdienol-baited traps, whileMonochamus clamator (Cerambycidae) andDendroctonus ponderosae (Scolytidae) were attracted to ß-phellandrene. Attraction of all eight species increased with increasing release rates of ipsdienol and/or ß-phellandrene.

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.

In south-central British Columbia, the attraction ofIps latidens (LeConte) to its pheromone, ipsenol, was inhibited by (S)-(+)-ipsdienol, a pheromone forI. pini (Say). (R)-(-)-lpsdienol had no effect onI. latidens. (S)-(+)-lpsdienol probably plays a role in interspecific communication between the two species, facilitating reductions in interspecific competition for breeding material and/or interspecific mating interference.

The ability of (E)- and (Z)-6-nonen-2-one to serve as precursors of the common scolytid pheromonesEndo- andexo-brevicomin was examined in vivo. When mountain pine beetles (MPB),Dendroctonus ponderosae Hopkins, or western balsam bark beetles (WBBB),Dryocoetes confusus Swaine, were exposed to [6,7-D2](E)-6-nonen-2-one, theEndo-brevicomin produced was enriched with two deuterium atoms per molecule (as determined by GC-MS), indicating that (E)-6-nonen-2-one served as a precursor of this pheromone. Similarly, when the beetles were exposed to [4,4-D2](Z)-6-nonen-2-one, theexo-brevicomin produced was enriched with two deuterium atoms per molecule. Evidence in support of biological relevance of the latter observation include: (1) (Z)-6-nonen-2-one was found in the volatiles of male MPBs and WBBBs, indicating that this is a natural metabolite; (2) theexo-brevicomin produced by MPB was shown to be of natural (+) chirality by complexation chromatography; and (3) female WBBBs and MPBs (which are not known to produceexo-brevicomin) produced significantly lessexo-brevicomin when exposed to the precursor than did the males.

Chemical analysis of whole body extracts and volatiles produced by feeding malesDryocoetes affaber (Mann.) disclosed (+)-exo-brevicomin and (+)-endo-brevicomin [(+)EXOB and (+)ENDOB], as the major insect-produced potential pheromones. Laboratory bioassays and field-trapping experiments demonstrated that (+)ENDOB is the main pheromone component, and (-)ENDOB has an inhibiting effect. EXOB either as (+) or (±) appears to be a multifunctional pheromone. It has a synergistic effect in blends of EXOB and ENDOB in ratios up to 1:1, and it is inhibitory at higher ratios. (-)EXOB was inactive. The most attractive blend forD. affaber was a 1:2 blend of (+)EXOB and (+)ENDOB. When this blend was compared with a 9:1 blend, the best known blend forDryocoetes confusus Swaine, the responses by beetles of each of the two species were highly specific, providing evidence for pheromonal exclusion between the two congenerics. We conclude that the combined effect of chirality and the ratio of geometrical isomers of brevicomin determines both the level of response and the species-specificity of the chemical signal inD. affaber.

In a field-trapping experiment, western balsam bark beetles,Dryocoetes confusus Swaine, were highly attracted to a 5:1 mixture of (±)-exo-and (±)-endo-brevicomin. Beetles in the sympatric speciesD. affaber (Mann.), were best attracted to a 1:1 blend of these semiochemicals [either (±):(±) or (±):(±)], suggesting that both geometrical isomers are pheromone components in these species. In laboratory bioassays and further field experiments, attraction ofD. confusus was greatest when the (+) enantiomers of both geometrical isomers of brevicomin were presented in a 9:1 ratio. Responses by maleD. confusus to attractive mixtures were reduced in the presence of (-)-exo-brevicomin. Exploitation of the complete range of variability in pheromone structure (both geometrical and optical isomerism) would allow for optimization and regulation of response levels within a species and also could maintain reproductive isolation among sympatric congeneric species primarily through production and response to species-specific blends.