Identification of Semiochemicals Associated with Jeffrey Pine Beetle, Dendroctonus jeffreyi

Analysis of frass extracts and aerations from adult beetles confirmed earlier studies identifying 1-heptanol as a principal pheromone constituent produced by female Dendroctonus jeffreyi Hopkins. The aerations also indicated that males produced 33% (+) and 67% (–)-frontalin, previously unreported for this species, and >99% (+)-exo-brevicomin. Both males and females were responsive to these compounds in electrophysiological studies. Laboratory bioassays and field trapping experiments indicated that males and females were attracted to a mixture of 1-heptanol plus the principal host resin component heptane, but females were less attracted than males. Inclusion of racemic exo-brevicomin at 0.1% concentration in the traps increased the response of females. Inclusion of racemic frontalin above a 1% concentration in the normally attractive lures blocked arrival of beetles to the traps. While the female-produced pheromone components and host synergists are very different between the sibling species D. jeffreyi and Dendroctonus ponderosae Hopkins, the principal male-produced compounds are the same, and the response of the female beetles to those compounds appears to be similar.     

Response of mountain pine beetle,Dendroctonus ponderosae Hopkins,and pine engraver,Ips pint (SAY), to ipsdienol in southwestern British Columbia

In bioassays conducted with walking beetles in the laboratory (S)–(+)–, (R)-(–)-, and (±)-ipsdienol were attractive alone, but reduced the attraction of both sexes of the mountain pine beetle,Dendroctonus ponderosae Hopkins, to extracts of female frass. Field trapping studies indicated that attraction ofD. ponderosae to a stimulus composed of myrcene +trans-verbenol +exo-brevicomin was significantly reduced with the addition of (±)- and sometimes (S)-(±)-ipsdienol. Thus, (S)-(+)-ipsdienol produced by males of this species may act as an antiaggregation pheromone. (S)-(+)-Ips-dienol is thought to function as a repellent allomone against the pine engraver,Ips pini (Say), in regions whereI. pini utilizes (R)-(–)-ipsdienol as an aggregation pheromone. However, in southwestern British ColumbiaI. pini was attracted to the (±)-ipsdienol used in field bioassays ofD. ponderosae, a finding consistent with the production of both enantiomers byI. pini in this region. When presented with the ternary semiochemical bait forD. ponderosae, (±)-ipsdienol was not attractive toI. pini. Thus, the activity of (S)-(+)-ipsdienol as a repellent allomone againstI. pini seems to be replaced in southwestern British Columbia by the inhibitory effects of myrcene,trans-verbenol,exo-brevicomin, or some combination thereof.Research supported in part by Natural Sciences and Engineering Research Council, Canada, Operating Grant A3881, Strategic Grant G1039, a Postgraduate Scholarship to D.W.A. Hunt, and the Science Council of British Columbia Grant 1 (RC-10)     

Interspecific effects of pheromones on the attraction of the bark beetles,Dendroctonus brevicomis andIps paraconfusus in the laboratory

Dendroctonus brevicomis was attracted to a mixture of theIps paraconfusus pheromones, ipsenol,cis-verbenol, and ipsdienol at 10^–9 g each/l but was not attracted to these pheromones at higher and lower release rates.I. paraconfusus was not attracted to theD. brevicomis pheromonesexo-brevicomin, frontalin, and myrcene at any release rate tested. Increased release rates of a mixture of the three pheromones ofI. paraconfusus inhibited the attraction ofD. brevicomis to its synthetic pheromones. A mixture of ipsenol + ipsdienol orcis-verbenol alone failed to cause inhibition indicating that at least two of theI. paraconfusus pheromones are required to inhibit the response ofD. brevicomis. The pheromones ofD. brevicomis did not inhibit the attraction ofI. paraconfusus to its pheromones; however, verbenone was a potent inhibitor.Coleoptera: Scolytidae. This paper is based in part upon a dissertation submitted by J.A.B. to the University of California, Berkeley, in partial fulfillment of the requirements for the Ph.D. degree in entomology, June 1978. These studies were supported by the Rockefeller Foundation; USDA Forest Service; Regional research project W-1 10, 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. The findings, opinions, and recommendations are not necessarily those of the University of California or the funding agencies.     

Male-specific conversion of the host plant compound,myrcene, to the pheromone, (+)-ipsdienol,in the bark beetle,Dendroctonus brevicomis

When both sexes of the bark beetle,Dendroctonus brevicomis LeConte, were exposed to vapors of myrcene from ponderosa pine, only the male produced (+)-ipsdienol. In the field, racemic ipsdienol significantly reduced the attraction of both sexes in flight to a mixture of myrcene and the aggregation pheromones,exo-brevicomin and frontalin. This suggests that ipsdienol may be involved in regulating colonization density ofD. brevicomis. The implications of the biosynthesis of various enantiomers of ipsdienol byD. brevicomis and the cohabitating bark beetles,Ips paraconfusus andI. pini, in relation to their behavioral responses are discussed in regard to reducing interspecific competition.Coleoptera: Scolytidae.     

Interspecific inhibition of the response of the bark beetles,Dendroctonus brevicomis andIps paraconfusus,to their pheromones in the field

Ponderosa pine logs infested withIps paraconfusus males inhibited the attraction ofDendroctonus brevicomis in the field to either attractive logs cut from a ponderosa pine tree under attack byD. brevicomis or to their synthetic pheromones,exo-brevicomin, frontalin, and myrcene. Logs cut from trees under attack byD. brevicomis inhibited the response ofI. paraconfusus to logs infested with maleI. paraconfusus.Exo-brevicomin, frontalin, and myrcene did not inhibit their response but verbenone did. Verbenone was found in maleD. brevicomis dissected from attractive logs under attack during the same time the response ofI. paraconfusus was inhibited by these logs.Trans-verbenol andexo-brevicomin were found in femaleD. brevicomis while verbenone,trans-verbenol, and frontalin were found in maleD. brevicomis in relatively large amounts near the beginning of the aggregation phase of host colonization. All of these compounds had decreased at a similar rate 5 days later. This gradual decrease inexo-brevicomin and frontalin probably caused the observed reduction in attraction. The ecological significance of these compounds in relation to termination of the aggregation phase ofD. brevicomis and reduction of interspecific competition is discussed.Coleoptera: Scolytidae. This paper is based in part upon a dissertation submitted by J.A.B. to the University of California, Berkeley, in partial fulfillment of the requirements for the PhD in entomology. These studies were supported in part by the Rockefeller Foundation; U.S. Forest Service; Regional research Project W-110, S.E.A./ U.S.D.A.; and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BMS 75-04223) to the University of California.     

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.     

Electrophysiological and Olfactometer Responses of Two Histerid Predators to Three Pine Bark Beetle Pheromones

We measured electrophysiological responses in the antennae of two predaceous hister beetles, Platysoma parallelum and Plegaderus transversus, exposed to racemic mixtures of primary aggregation pheromones of scolytid bark beetle prey, ipsenol, ipsdienol, and frontalin. No significant differences were found for either histerid species between male and female antennal responses to any of the three pheromones. Measurement of antennal threshold responses indicated that Pla. parallelum has increasing antennal sensitivity to ipsdienol, ipsenol, and frontalin. In contrast, Ple. transversus exhibited similar detection thresholds to all three pheromones. Pla. parallelum antennae exhibited different response amplitudes to the three pheromones at quantities above the detection threshold, while Ple. transversus had similar responses to each. Behavioral responses to the same three pheromones were evaluated for both histerid species using pedestrian olfactometer bioassays. Both species were attracted to frontalin and ipsenol, but not ipsdienol. Pla. parallelum was significantly more attracted to frontalin than ipsenol, while Ple. transversus showed no significant preference for either compound. Our results suggest that histerids that prey upon pine bark beetles may have different host or host habitat preferences, which could reduce interspecific competition.     

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.     

Stereospecific antennal response by red turpentine beetle,Dendroctonus valens to chiral monoterpenes from ponderosa pine resin

The antennal response ofDendroctonus valens to host monoterpenes from the resin of ponderosa pine was studied using the electroantennogram (EAG) technique. Male and female beetles were given a single dose of each of 11 different monoterpenes. Response amplitude to the different compounds did not vary between sexes and was generally well correlated with results from field attraction studies. Response to (S)-(–)--pinene was greatest. The relative amplitude of the responses to the (R)-(+) and (S)-(–) enantiomers of a-pinene, however, were reversed from their relative attractiveness in the field. A dose-response study was conducted for the (R)-(+) and (S) -(–) enantiomers of a-pinene, plus a reciprocal differential saturation test with successive doses of first one enantiomer of-pinene and then the other. Comparison of EAG traces suggests different receptors for the two stereoisomers of-pinene. Differential saturation curves suggest that while one set of receptors may respond to both enantiomers, some receptors respond only to the (S)-(–) enantiomer.     

Effect of mating on terminating aggregation during host colonization in the bark beetle,Ips paraconfusus

Attraction of maleIps paraconfusus to male-infested ponderosa pine logs was inhibited by volatiles from logs infested with mated males and females over an 8-day period in the field. The response of females during this time was not significantly inhibited by these volatiles. Synthesis of the male-specific pheromones, ipsenol and ipsdienol, appeared negligible after 8 days in males allowed to mate with 3 females in these logs while males alone contained levels of these pheromones at about half their maximum rate. The decline in pheromone production in mated males appears to result, at least in part, from a reduction in the activity of the biosynthetic system that converts the host monoterpene, myrcene, to ipsenol and ipsdienol. Mating and feeding have apparently no effect on the biosynthetic system that converts the host monoterpene, (–)--pinene, to the pheromone,cis-verbenol in either males or females. The reduced production and release of pheromones by males after mating appears to play a major function in the process of terminating the aggregation phase of host colonization.     

Antennnal olfactory and behavioral response of southern pine beetle,Dendroctonus frontalis,to analogs of its aggregation pheromone frontalin

Antennal olfactory (electroantennogram) and laboratory and field behavioral tests were carried out on the response ofDendroctonus frontalis to its aggregation pheromone frontalin and analogs. The analogs were compounds modified by altering the position and methyl groups and/or by their deletion. Any modification to the frontalin structure significantly reduced both the antennal olfactory and behavioral response byD. frontalis. Beetle response, although significantly reduced, was elicited at the receptor level and in a laboratory bioassay by all analogs. However, only one analog (endo-5,7-dimethyl-Frontalin) elicited significant response from field populations of the beetle.Texas Agricultural Experiment Station paper TA-22507. The work was funded in part by McIntire-Stennis project 1525 and by an operating grant from the Alberta Forest Service through the Forest Development Research Trust Fund. The findings, opinions, and recommendations expressed are those of the authors and not necessarily those of the U.S. Department of Agriculture. All programs and information of the Texas Agricultural Experiment Station are available without regard to race, ethnic origin, religion, sex, or age.     

Effect of verbenone on response ofDendroctonus brevicomis toexo-Brevicomin,frontalin, and myrcene

exo-Brevicomin (E), frontalin (F), and myrcene (M) were released at two rates 10-fold apart with verbenone at four rates 10-fold apart, and without verbenone in plots with one trap on a vertical cylinder at the pheromone source and one trap on each of four cylinders 5 m away. Catch of the western pine beetleDendroctonus brevicomis decreased with increasing levels of verbenone at both release rates of EFM, but not all differences in catch were statistically significant. Significantly more beetles were caught at the high rate of EFM than at the low rate, combining all rates of verbenone. The percent of total beetles caught at the center trap tended to decrease with increasing rates of verbenone, but the only statistically significant differences were at the low rate of EFM.Coleoptera: Scolytidae.     

Quantitative estimates of the western pine beetle attractive pheromone components,exo-brevicomin,frontalin, and myrcene in nature

Three parameters are described for estimating the natural occurrence of chemically defined insect pheromones: (1) the rate and duration of release by the insect, (2) the density of the pheromone-emitting insect population in both time and space, and (3) dispersal and degradation rates of the chemicals. Each of these parameters, except dispersal, was estimated for a population ofDendroctonus brevicomis LeC, and its three component attractive pheromones. A single generation of 610,000 beetles, believed to comprise the entire population in a 65-km² forest, was estimated to have released 0.78, 3.7, and 370.5 g of frontalin,exo-brevicomin, and myrcene, respectively, within a 30-day period. Dendroctonus brevicomis Le Conte (Coleoptera: Scolytidae).Parts of this report were prepared for the U.S. Forest Service to accompany a future application to the Environmental Protection Agency for registration of these attractants for use in the suppression ofD. brevicomis populations. The research was supported by grants to the University of California (D.L. Wood) from the National Science Foundation/Environmental Protection Agency (NSF-6B-34718/BMS75-04223), Forest Service, U.S. Department of Agriculture and Rockefeller Foundation. The findings, opinions, and recommendations are those of the authors and not necessarily those of these institutions.     

Disruption by Conophthorin of the Kairomonal Response of Sawyer Beetles to Bark Beetle Pheromones

Antennally active nonhost angiosperm bark volatiles were tested for their ability to reduce the response of three common species of coniferophagous wood-boring Cerambycidae to attractant-baited multiple funnel traps in the southern interior of British Columbia. Of the nonhost volatiles tested, only conophthorin was behaviorally active, disrupting the attraction of sawyer beetles, Monochamus spp., to traps baited with the host volatiles -pinene and ethanol and the bark beetle pheromones ipsenol and ipsdienol. Conophthorin did not affect the attraction of sawyer beetles to the host kairomones -pinene and ethanol in the absence of bark beetle pheromones, nor did it have any behavioral effect on adults of Xylotrechus longitarsis, which were not attracted to bark beetle pheromones. These results indicate that conophthorin does not act as a general repellent for coniferophagous Cerambycidae, as it seems to do for many species of Scolytidae, but has the specific activity of disrupting the kairomonal response of sawyer beetles to bark beetle pheromones.     

Individual variation in aggregation pheromone content of the bark beetle,Ips typographus

The total amounts of, and proportions among, components of the aggregation pheromone produced byIps typographus were found to vary considerably among individuals excised from attacks on standing spruce trees. Chemical analyses of 392 individual male beetles were made by GC-MS. Both unmated and mated males had log-normal frequency distributions in their content of the pheromone components 2-methyl-3-buten-2-ol (MB) andcis-verbenol (cV), since a large fraction of males had a low content. The amount of MB in male hindguts varied independently of cV and the other oxygenated monoterpenes, while the amount of cV covaried with the other pinene alcohols and showed a variation between beetles from different spruce trees. Mated males had, on average, lower amounts of MB than unmated, while the average content of cV in mated males varied with the resin content of their host trees. Ipsdienol and ipsenol were only found in mated males, but in less than 40% and 10%, respectively, of these mated males. Even-aged males exposed to -pinene in the laboratory showed slightly less variation in the amounts of verbenols, and the variations in ratio between cV and tV were similar to those among males attacking the same spruce tree.Coleoptera, Scolytidae.This study was made within the Swedish project Odour Signals for Control of Pest Insects.     

Pheromonal attraction and allomonal interruption ofIps pini in California by the two enantiomers of ipsdienol

Air containing volatile compounds from around maleIps pini boring in ponderosa pine logs from California was condensed, fractionated by GC, and assayed in the laboratory and field. The only fraction that showed consistent activity in laboratory assays contained a single compound identified as ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol). Synthetic racemic ipsdienol showed no activity in either the laboratory or field. However, (–)-ipsdienol, the naturally occurring enantiomer, was attractive toI. pini in the laboratory and field, whereas (+)-ipsdienol interrupted the response ofI. pini to a natural source of attraction in field tests. (–)-Ipsdienol is a major component of the attractant pheromone of this species, since its level of activity in laboratory assays was quantitatively comparable to that of the condensed volatiles, and it was as attractive as maleI. pini boring in ponderosa pine in the field. (+)-Ipsdienol is a component of the pheromone of the competing species,I. paraconfusus.(C.B.R.I. Contribution No. 1043.)     

Variation of enantiomeric composition of α-pinene in norway spruce,Picea abies,and its influence on production of verbenol isomers byIps typographus in the field

The enantiomeric composition of -pinene in individual Norway spruce trees [Picea abies (L.) Karst.] was determined on a chiral GC column after stereoselective hydroboration-oxidation followed by a reaction with isopropyl isocyanate to form the carbamate derivative. The enantiomeric composition varied considerably between trees of different genetic origin. There was a strong correlation between the chirality of -pinene in host spruce trees and thecis/trans ratio of verbenols found in the hindguts of the bark beetleIps typographus (L.) infesting the trees.Coleoptera; Scolytidae.Parts of this work have been presented at the 14th International Symposium on the Chemistry of Natural Products in Poznan, Poland, July 9–14, 1984.     

Pheromone biosynthetic pathways: Conversion of ipsdienone to (−)-ipsdienol,a mechanism for enantioselective reduction in the male bark beetle,Ips paraconfusus

The enantiomeric composition of the pheromone components (+)-ipsdienoI, e.e. 87.6%, and (–)-ipsenol, e.e. 93.8%, produced by the male bark beetleIps paraconfusus (Scolytidae) under natural conditions was determined by HPLC separation of their diastereomeric ester derivatives. Males confined in an atmosphere of ipsdienone produced (–)-ipsdienol, e.e. 28%, and (–)-ipsenol, e.e. 86%, indicating an enantiomeric selectivity in the conversion of the ketone to the alcohols. These findings demonstrate an enantioselective conversion mechanism in the biosynthetic pathway to the pheromones from myrcene, a host-plant terpene.     

Interruption of response ofDendroctonus brevicomis to its attractive pheromone by components of the pheromone

The catch of the western pine beetle,Dendroctonus brevicomis, at an attractive source of racemicexo-brevicomin, racemic frontalin, and myrcene was reduced by surrounding the source with a grid of 48 stations releasing all three compounds together, orexo-brevicomin alone or myrcene alone. Each compound was released at the rate of 2 mg/24 hr/station. The catch at an attractive bolt cut from a tree being colonized byD. brevicomis was not reduced byexo-brevicomin, but was reduced by the combination ofexo-brevicomin, frontalin, and myrcene in one of two tests. When a transect of traps was placed across a 0.81-hectare plot at six of the 48 stations releasing all three compounds, more beetles were caught at outer than at inner traps. More beetles were caught at unbaited traps on trees in a plot when the three compounds were released than when onlyexo-brevicomin or no compounds were released. A few trees were attacked byD. brevicomis in some of the plots. The antiattractant verbenone released from 48 stations at the rate of 4 mg/24 hr/station did not reduce the catch at an attractive tree bolt.Coleoptera: Scolytidae.These studies were supported by the Forest Service, U.S. Department of Agriculture, and in part by grants to the University of California from the U.S. National Science Foundation and U.S. Environmental Protection Agency (NSF GB-34718/BMS 75-04223) and the Rockefeller Foundation. The findings, opinions, and recommendations are not necessarily those of the funding agencies. Mention of commercial enterprises or products is only for information.     

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.