Kairomone response inThanasimus predators to pheromone components ofIps typographus

Thanasimus formicarius (L.) responds to racemic ipsdienol and ipsenol and less to (S)-cis-verbenol. All three are pheromone components in several bark beetles of the genusIps. Synergistic effects appeared when the components were combined. Methylbutenol alone, the specific pheromone component ofIps typographus, elicited no response, but synergestic effects appeared when methylbutenol was combined withcis-verbenol and ipsdienol. The sympatric speciesThanasimus femoralis (Zett.) responds to (S)-cis-verbenol, while ipsdienol and ipsenol synergize the response.     

Sensitivity of antennae of male and femaleIps paraconfusus (Coleoptera: Scolytidae) to its pheromone and other behavior-modifying chemicals

The antennal sensitivities of both male and femaleIps paraconfusus were found generally to be greatest for conspecific aggregation pheromones (ipsdienol, ipsenol); intermediate for an additional conspecific pheromone (cis-verbenol), an aggregation synergist (2-phenylethanol), and pheromones/allomones of sympatric species (trans-verbenol, verbenone, and frontalin); and lowest for both host terpenes (alpha-pinene and myrcene) and other bark beetle-produced odorants (exo-brevicomin and linalool). Of the enantiomeric compounds tested, antennae of both sexes did not differ in sensitivity between thetrans-verbenol enantiomers at low dosage levels; but at higher dosages, the conspecific-produced enantiomer, (1R,4S,5R)-(+)-trans-verbenol, elicited larger mean EAG responses than its antipode, (1S,4R, 5S)-(?)-trans-verbenol. At the mid-dosage range, female antennae tended to be slightly more responsive to (S)-(?)-verbenone than to (R)-(+)-verbenone, while male antennae were equally responsive to stimulations by either verbenone enantiomer. In field bioassays there was a large and significant reduction in trap catches ofI. paraconfusus on traps where the (S)-(?)- or (R)-(+)-enantiomers of verbenone were evaporated beside logs containing boring conspecific males. Only when the (S)-(?)-enantiomer of verbenone was evaporated beside logs containing boring males did the sex ratio ofI. paraconfusus trapped shift from female-dominated to male-dominated attraction. Thus both physiological and behavioral data suggest a differential chiral sensitivity of female beetles for the verbenone enantiomers. The relative sensitivities between different chiral compounds derived from one or the other of the common precursoral host terpenes, (S)-(?)- and (R)-(+)alpha-pinene or myrcene, are discussed.     

Sensitivity of antennae of male and femaleIps paraconfusus (Coleoptera: Scolytidae) to their natural aggregation pheromone and its enantiomeric components

Antennae of male and femaleIps paraconfusus were equally and highly sensitive to their male-produced, multicomponent aggregation pheromone. Female and male antennae were highly sensitive to the pheromonal component, (S)-(–)-ipsenol, but essentially insensitive to its antipode, (R)-(+)-ipsenol. Further, female and male antennae were more sensitive to the pheromonal component, (S)-cis-verbenol, than to its antipode, (R)-cis-verbenol. Dramatic sexual dimorphism in chiral sensitivity to the ipsdienol enantiortiers was found, with female antennae being more sensitive to the conspecific pheromonal enantiomer, (S)-(+)-ipsdienol, and male antennae being more sensitive to the antipode, (R)-(–)-ipsdienol. Since (R)-(–)-ipsdienol is the principal pheromone of CaliforniaIps pini and interruptsI. paraconfusus aggregation, male antennae appear to be more sensitive to an interspecific allomone than a conspecific pheromone. Of the conspecific pheromonal enantiomers, both male and female antennae were most sensitive to (S)-(+)-ipsdienol, intermediately sensitive to (S)-(–)-ipsenol, and least sensitive to (S)-cis-verbenol. However, when enantiomeric sensitivities were compared to the estimated concentrations of these components in the natural pheromone, (S)-(~)-ipsenol tended to equal or approach the potency of (S)-(+)-ipsdienol as an antennal stimulant, while antennal responsiveness to (S)-cis-verbenol was dramatically less than for the other two pheromonal components. The behavioral implications of such physiological sensitivities are discussed in regard to perception of multicomponent synergistic pheromones and the relative efficacy of each component as an orientation cue.This paper is based in part upon a dissertation submitted to the University of California, Davis, in partial fulfillment of the requirements for the PhD in entomology.     

Olfactory receptor cell responses ofIps grandicollis (eichhoff) (Coleoptera: Scolytidae) to intra- and interspecific behavioral chemicals

Electrophysiological recordings from antennal olfactory receptor cells were obtained fromIps grandicollis. Recordings were made from olfactory receptor cells from nine regions of the antennae in response to stimulation with the semiochemicals-pinene, frontalin,endo-brevicomin, verbenone,trans-verbenol,cis-verbenol, ipsdienol, and ipsenol. In many cases, up to two cells were recorded concurrently from the same location. When compared to males, females had a greater percentage of cells responsive to the primary pheromones ofDendroctonus frontalis, frontalin andtrans-verbenol, and ofIps spp., ipsdienol and ipsenol. Among females, more cells responded totrans-verbenol and theIps-produced volatiles than to host or otherD. frontalis-produced compounds. Olfactory cells of males responded mostly tocis-verbenol, followed by-pinene, verbenone,trans-verbenol, andendo-brevicomin. Of those cells responsive primarily to one compound, the greatest percentage were responsive totrans-verbenol in females and to verbenone in males. The response of the antennal olfactory receptor cells to semiochemicals used by male and femaleI. grandicollis is consistent with the presence of these compounds during the host colonization period for each sex. Our results, which show a lack of specificity in most pheromone and host odor receptor cells, is in contrast with previously published accounts of olfactory receptor cell specificity in otherIps species.     

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.     

Quantitative variation of pheromone components in the spruce bark beetleIps typographus from different attack phases

Ips typographus beetles were collected in the field, separated into eight attack phases (from beetles walking on the trunk of a tree under attack to those excavating gallery systems with a mother gallery longer than 4 cm), and immediately frozen in liquid nitrogen. 2-Methyl-3-buten-2-ol,cis- andtrans-verbenol, verbenone, myrtenol, trans-myrtanol, ipsenol, ipsdienol, and 2-phenylethanol were quantified from excised hindguts against an internal standard, heptyl acetate, in the extraction solvent. Methylbutenol, the pinene alcohols, and 2-phenylethanol showed the same pattern of variation between attack phases in males, with the largest amounts present before accepting females and then a fast decline. Ipsenol and ipsdienol were not detected in males before the females were accepted, and the amounts increased when the females start their egg laying. Verbenone occurred only in trace amounts. The beetles were sampled from five Norway spruce trees (Picea abies) of differing resin flow. The correlations between the nine pheromone components and five major host monoterpenes in the gut showed that the variation in the amount of methyl-butenol, ipsenol, and ipsdienol could not be explained by the variation in the amounts of host monoterpenes. In contrast over 80% of the quantitative variation ofcis-verbenol,trans-verbenol, and myrtenol was explained by the amount of -pinene. The nine pheromone components from 36 individual males were also quantified. Both methylbutenol andcis-verbenol showed a large variation in both amounts and proportions. Females containedtrans-verbenol and traces of most other components found in males. When accepted by the male, they also contained a female-specific compound, -isophorone. Behavioral and biosynthetic implications of the results are discussed.Coleoptera: Scolytidae.This study was made within the Swedish project Odour Signals for Control of Pest Insects.     

Volatiles released from individual spruce bark beetle entrance holes Quantitative variations during the first week of attack

Volatiles released from individual entrance holes of eight spruce bark beetles (Ips typographus) were collected during the first week of attack on a resistant host tree. In order to quantify the release of the highly volatile 2-methyl-3-buten-2-ol (MB) from attacking males, a new method was developed with deuterated quantification standard released at the time of collection. The amounts of collected volatiles, as analyzed by GC and GC-MS, showed a large variation between individual holes and also between subsequent entrainments from the same hole. Most of the quantified compounds on the average have two maxima, with a pronounced intervening depression. The amounts of releasedcis-verbenol (cV) increased five times during the first two days, while the amounts of MB were consistently high. The attacked spruce tree was not taken by the beetles, and the average amounts of the two aggregation pheromone components, MB and cV, increased again after the first maxima. The first peak of oxygenated monoterpene, released in the beginning of the attack containing -terpineol, terpinen-4-ol, bornyl acetate,trans-pinocarveol, and verbenone, was possibly due to spontaneous oxidation of monoterpene hydrocarbons from the tree. Microorganisms established in the gallery wall phloem probably participated in the production of oxygenated monoterpenes during the second increase.Ips typographus (Coleoptera: Scolytidae).     

Ipsenol: an aggregation pheromone forIps latidens (Leconte) (Coleoptera: Scolytidae)

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.     

Aggregation Pheromone of the Qinghai Spruce Bark Beetle, <Emphasis Type="Italic">Ips nitidus</Emphasis> Eggers

Volatiles from hindgut extracts of males of the Qinghai spruce bark beetle, Ips nitidus, from different attack phases (phase 1: unpaired males and phases 2–4: males joined with one to three females) and hindgut extracts of mated females were analyzed by gas chromatography–mass spectrometry (GC–MS)/flame ionization detection (FID) with both polar and enantioselective columns. The GC–MS/FID analyses demonstrated that unpaired males from attack phase 1 (nuptial chamber constructed) produced 2-methyl-3-buten-2-ol, approx. 74%-(−)-ipsdienol, and (−)-cis-verbenol as major hindgut components, and (−)-trans-verbenol, (−)-ipsenol, (−)-verbenone, myrtenol, and 2-phenylethanol as minor or trace components. The quantities of 2-methyl-3-buten-2-ol and especially ipsdienol decreased after mating during phases 2–4, whereas the quantities of (−)-cis- and (−)-trans-verbenol did not change. In contrast, the quantity of (−)-ipsenol seemed to increase as mating activity progressed. After mating with three females (harem size = 3; phase 4), only trace to small amounts of male-specific compounds were detected from I. nitidus male hindguts. Chemical analysis of the hindgut extracts of mated females showed only trace amounts of semiochemicals. A field-trapping bioassay in Qinghai, China showed that the four-component “full blend” containing the three major components, 2-methyl-3-buten-2-ol, (±)-ipsdienol, and (−)-cis-verbenol, plus a minor component, (−)-trans-verbenol, caught significantly more I. nitidus (♂/♀ = 1:2.2) than did the unbaited control and two binary blends. The replacement of (±)-ipsdienol with nearly enantiomerically pure (−)-ipsdienol in the “full blend” significantly reduced trap catches, which suggests that both enantiomers are needed for attraction. On the other hand, removal of (−)-trans-verbenol from the active “full blend” had no significant effect on trap catches. Our results suggest that the three major components, 2-methyl-3-buten-2-ol, 74%-(−)-ipsdienol, and (−)-cis-verbenol (at 7:2:1), produced by unpaired fed males, are likely the aggregation pheromone components of I. nitidus, thus representing the first characterization of an aggregation pheromone system of a bark beetle native solely to China.     

Pheromones in white pine cone beetle,Conophthorus coniperda (schwarz) (Coleoptera: Scolytidae)

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.     

Conversion of verbenols to verbenone by yeasts isolated fromDendroctonus ponderosae (Coleoptera: Scolytidae)

A variety of symbionts associated with bark beetles are capable of producing compounds that are used as pheromones by their hosts. We report that two yeasts associated withDendroctonus ponderosae Hopkins,Hansenula capsulata Wickerham, andPichiapinus (Hoist) Phaff, are capable of convertingcis- andtrans-verbenol efficiently into verbenone.trans-Verbenol, which is produced by femaleD. ponderosae, acts as an aggregation pheromone for this scolytid, while verbenone, which other studies have indicated that microbe-reducedD. ponderosae are incapable of producing, acts as an antiaggregation pheromone.D. ponderosae appears to rely primarily on microbial symbionts for terminating aggregation and mass attack on individual host trees.Research supported in part by the Natural Sciences and Engineering Research Council, Canada, Operating Grant A3881, and Strategic Grant G1039.     

Differences in attraction to semiochemicals present in sympatric pine shoot beetles,Tomicus minor andT. piniperda

The chemical ecology of host- and mate-finding in the pine shoot beetles,Tomicus minor andT. piniperda, was studied in southern Sweden. Beetles were collected in the field from defined attack phases on Scots pine. Using gas chromatography-mass spectroscopy, a number of oxygen-containing monoterpenes, e.g., 3-carene-10-ol, myrtenol,trans-verbenol, and verbenone, were identified from hindgut extracts of both sexes of both species. Compared toT. minor,T. piniperda contained additional compounds and in larger amounts. The amounts were highest in both species at the time when the beetles had bored into contact with the resin-producing xylem-phloem tissue. The synthesis of (1S,6R)-3-carene-10-ol by photooxidatipn of (+)-(1S,6R)-3-carene is described. In comparative electroantennogram (EAG) measurements on males and females of both species, the most active of the tested compounds wastrans-verbenol. Laboratory bioassays of walking beetles showed thatT. piniperda was attracted to uninfestèd pine logs.T. minor was more strongly attracted to pine logs infested with females than to uninfested pine logs, indicating a female-produced aggregation pheromone. Field tests confirmed thatT. piniperda was strongly attracted to pine logs. The attraction ofT. minor to logs was significant only when logs were combined with racemictrans-verbenol and (1S,6R)-3-carene-10-ol.T. minor was also attracted to a combination of these monoterpene alcohols alone. We suggest that host and mate location inT. piniperda is achieved by means of a kairomone composed of host monoterpenes, whileT. minor utilizes a primitive pheromone synergized by host odors. Evolution of host colonization strategies of the two beetles are discussed.Coleoptera: Scolytidae.This study was made within the project Odour signals for control of pest insects.     

Field response of spruce bark beetle,Ips typographus,to aggregation pheromone candidates

Six compounds previously identified from hindguts of unmated maleIps typographus (L.) during host colonization: 2-methyl-3-buten-2-ol (MB),cis-verbenol (cV),trans-verbenol (tV), myrtenol (Mt),trans-myrtanol (tM), and 2-phenylethanol (PE), were tested for their attractivity in the field with a subtractive method. The amounts of MB and cV released from a pipe trap were similar to those given off from the commercial bait Ipslure as well as that from a Norway spruce tree,Picea abies (L.) Karst., under mass attack. The blend of the compounds became nonattractive when either MB or cV was subtracted, while subtraction of any of the other four compounds had no effect. Addition of ipsdienol (Id) to the blend did not significantly increase the attraction. In a second comparative test, the addition of three compounds as a group (tV + Mt + PE) to MB + cV again had no effect on the attraction, but the addition of Id increased the catch somewhat. Addition of host logs to a bait releasing MB + cV at a rate lower than in previous experiments did not influence the attraction to pipe traps. Sticky traps containing natural pheromone sources (50 males in a log), which released 1–5 mg/day of MB as determined by aerations with deuterated MB as internal standard, were less attractive than a synthetic source releasing similar amounts of MB.Coleoptera: Scolytidae.This study was made within the Swedish project Odour Signals for Control of Pest Insects.     

Effects of verbenone andtrans-verbenol on the response ofDendroctonus brevicomis to natural and synthetic attractant in the field

Verbenone andtrans-verbenol were investigated as candidate interruptants for use as tree protectants. Verbenone andtrans-verbenol, pheromones released byDendroctonus brevicomis during host colonization, reduced the trap catch ofD. brevicomis near sources of the attractant composed ofexo-brevicomm, frontalin, and myrcene. Catch reduction at some trap positions was greater at a high release rate than at a low release rate oftrans-verbenol alone and of the combination of verbenone plustrans-verbenol. Verbenone also reduced catches at traps baited with attractive bolts from trees under attack byD. brevicomis. Attempts to use verbenone to protect living trees fromD. brevicomis attack were inconclusive.Coleoptera: Scolytidae.This research was supported in part by the Forest Service, U.S. Department of Agriculture, and in part by grants from the National Science Foundation/Environmental Protection Agency (grant NSF-6B-34718/BMS75-04223), and in part by grants from the Rockefeller Foundation to the University of California. Mention of a proprietary or commercial product does not constitute recommendation or endorsement of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that also may may be suitable.     

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.     

Semiochemicals produced by western balsam bark beetle,Dryocoetes confusus Swaine (Coleoptera: Scolytidae)

The most prominent beetle-produced volatiles identified in the abdominal extracts of maleDryocoetes confusus Swaine after they had bored for 24 hr in logs of subalpine fir,Abies lasiocarpa (Hook.) Nutt. were:exo andendo-brevicomin,trans-verbenol, verbenone, myrtenol,trans-pinocarveol,cis- andtrans-p-menthen-7-ol, 3-caren-10-ol, and several monoterpenes and sesquiterpenes. Myrtenol was the only conspicuous compound in extracts from males that had been exposed toA.lasiocarpa resin volatiles for 24 hr. Laboratory bioassays indicated that both (–)- and (+)-exo-brevicomin were attractive to femaleD. confusus, and that the (–) enantiomer did not inhibit response to its antipode. Results from field trapping experiments indicated that bothero-brevicomin and myrtenol are aggregation pheromones forD. confusus.exo-Brevicomin baits were effective in causing attack byD. confusus on baited and surrounding trees, suggesting that this pheromone may have utility in manipulating populations of the beetle.Research supported by the Natural Sciences and Engineering Research Council of Canada, Operating Grants A3881 and A3706 and Strategic Grant G1039.     

Attractive and inhibitory pheromones produced in the bark beetle,Dendroctonus brevicomis,during host colonization: Regulation of inter- and intraspecific competition

Quantities of attractive (exo-brevicomin and frontalin) and inhibitory (trans-verbenol, verbenone, and ipsdienol) pheromones were monitored in both sexes ofDendroctonus brevicomis during their colonization of a ponderosa pine. Verbenone was found in males in the greatest amounts at the time of landing, and it declined more rapidly than the other pheromones in either sex. The amounts of frontalin andexo-brevicomin in males and females, respectively, increased after initial boring within the host but began to decline after mating. The quantity oftrans-verbenol in both sexes (females had significantly more) declined more gradually thanexo-brevicomin, frontalin, and verbenone. Ipsdienol was found only in males during the initial stages of attack when encountering the resin. It is suggested that along with a general decline in all pheromonal components, a sufficient change in the ratio of the attractive pheromones to an inhibitory pheromone,trans-verbenol, may play a role in termination of aggregation.trans-Verbenol may also function along with verbenone and ipsdienol in limiting the density of attack and thus intraspecific competition. These inhibitory pheromones also appear to cause several competing species of bark beetle to avoid landing in areas infested withD. brevicomis, even when their own pheromone is present.Coleoptera:Scolytidae. These studies were supported in part by the Rockefeller Foundation, USDA Forest Service, Regional research project W-110, SEA/ USDA, and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BMS 75-04223) to the University of California.     

Attraction to pheromone sources of different quantity,quality, and spacing: Density-regulation mechanisms in bark beetleIps typographus

The density of bark-beetle colonization of a tree could be regulated by a quantitative effect of the pheromone signal from beetles in the tree (cessation of release of attractive pheromone) or by a qualitative effect (production of pheromone components inhibiting attraction). The quantitative hypothesis was tested onIps typographus by varying the release rate of the two known attractive compounds, 2-methyl-3-buten-2-ol (MB) and (4S)-cis-verbenol (cV). The highest number of beetles were captured at traps with the highest release rates. The catch was nearly proportional to the release of MB and cV at a distance between traps of 12 m or more. At 6-, 3-, and 1.5-m distances between traps deployed in a triangular arrangement there was still a good discrimination between release rates, but relatively more beetles, especially males, were caught on the blank. The lower release rates caught an equal sex ratio while the highest release rate caught only about 30% males. The qualitative hypothesis was tested by releasing the suspected inhibitors ipsdienol (Id) and ipsenol (Ie), from traps in the same amounts as cV. Only small effects were noted forI. typographus. However, the competitorI. duplicatus was attracted to Id and inhibited by Ie, while the predatorThanasimus formicarius was attracted to both compounds. On the other hand, when the ratio of Id or Ie to cV was 101 or 0.11 rather than 11, they affected the numbers ofI. typographus attracted. A small amount of Id combined with the attractants increased trap catch, while large amounts of Id or Ie decreased attraction, especially when combined. Attack density regulation is modeled as an effect of both quantitative and qualitative mechanisms acting in sequence.Coleoptera: Scolytidae.This study was made within the Swedish project Odour Signals for Control of Pest Insects..     

Effects of Enantiomeric Blend of Verbenone on Response ofIps paraconfusus to Naturally Produced Aggregation Pheromone in the Laboratory

The aggregation pheromone produced by maleIps paraconfusus (Coleoptera: Scolytidae) tunneling in Monterey pine,Pinus radiata, logs was trapped on Porapak Q. A concentration of an extract of trapped volatiles that attracted beetles was determined in the laboratory through a concentration–response analysis of walking behavior of males and females. The interruptant effects of four concentrations of verbenone on response to a constant concentration of this naturally produced aggregation pheromone were tested with males and females. Independent of its enantiomeric composition [99.5% (S)-(–), 93.1 % (S)-(–), and 98.3% (R)-(+)], verbenone significantly reduced the percentage of females (but not males) reaching the attractant source. However, when the time required for beetles of both sexes taken together to reach the attractant source was considered, verbenone of higher enantiomeric purity had a greater effect on beetle behavior. Solutions of 99.5% (S)-(–)- and 98.3% (R)-(+)-verbenone increased the time required for beetles to reach the attractive source when compared to 93.1% (S)-(–)-verbenone. When pooled across enantiomeric blends, increasing concentrations of verbenone resulted in slower responses in beetles that reached the attractant source within 2 min. Males and females did not respond to verbenone alone.     

Field responses of the western pine beetle1 and one of its predators to host- and beetle-produced compounds

The responses of the western pine beetle (Dendroctonus brev-icomis LeConte) andTemnochila chlorodia (Mannerheim) to candidate attractants—exo- andendo-brevicomm, frontalin,trans-verbenol, ver-benone, and ponderosa pine turpentine and its major monoterpene components—were quantified by counts of beetles on traps baited with the various attractants, singly and in combinations released simultaneously. Combinations ofexo-brevicomin and frontalin plus a monoterpene or turpentine were the most attractive toD. brevicomis. The responses to these attractant combinations were reduced when verbenone plustrans-verbenol were present. All single compounds and binary mixtures, exceptexo-brevicomin plus frontalin, were much less attractive.exo-Brevicomin was most attractive toT. chlorodia, and this response appeared to decrease when verbenone plustrans-verbenol were present.Coleoptera: Scolytidae.Coleoptera: Trogositidae.This research was supported in part by the Forest Service, U.S. Department of Agriculture, and in part by grants from the Rockefeller Foundation to the University of California. Commercial enterprises and products are mentioned solely for information, and do not imply endorsement by the sponsoring agencies and organizations.