Enantiomeric composition of ipsdienol: A chemotaxonomic character for north American populations ofIps spp. in thepini subgeneric group (coleoptera: Scolytidae)

Thirty-five populations ofIps pini (Say) and one population each ofIps avulsus (Eichhoff) andIps bonanseai (Hopkins) were analyzed for the enantiomeric composition of ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol). Populations ofI. pini occur as at least two distinct regional pheromone variants: New York type [32%-(–) to 56%-(–)-ipsdienol] and California type [94%-(–) to 98%-(–)-ipsdienol]. A third phenotype may occur in southeastern British Columbia, Idaho, and Montana [91%-(–) to 95%-(–)], possibly indicating a zone of hybridization. Populations of the New York type occur in southwestern British Columbia, Alberta, Saskatchewan, Minnesota, and Wisconsin suggesting a continuum through the Canadian provinces and Lake States. The presence of the New York type in western Canada is likely linked to the Quaternary history of the transcontinentally distributed host,Pinus banksiana Lamb. MaleI. avulsus [25%-(–)] and maleI. bonanseai [–29%-(–)] both produce ipsdienol, but not ipsenol. Production of ipsdienol by maleI. pini was evaluated in six differentPinus spp. hosts. Following transfer of maleI. pini to hosts other than the host of origin, the percentage of the (–)-enantiomer of ipsdienol declined when compared to production in the host of origin.     

(S)-(+)-Ipsdienol: Interspecific inhibition ofIps latidens (leconte) byIps pini (Say) (Coleoptera: Scolytidae)

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.     

Repeatability of female response to ipsdienol enantiomeric mixtures by pine engraver,Ips pini (Coleoptera: Scolytidae)

Repeatability, a measure of the proportion of variance in a character that occurs among rather than within individuals, is assessed for the phenotypic trait of female response preference for enantiomeric blends of ipsdienol inIps pini at two pheromone concentrations—1 µg and 5 g of ipsdienol. Average female response shows greater repeatability at the higher pheromone dosage when females are tested in two successive sets of five assays than when assayed in three successive sets or at the lower dosage. Repeatability within each set of five assays is highest for the first set and decreases thereafter. Thus the response phenotype of females for enantiomeric blends of ipsdienol in this experiment is context dependent; female choice of an enantiomeric blend differed between dosages and among sets of assays.     

Inter- and intrapopulation variation of the pheromone,ipsdienol produced by male pine engravers,Ips pini (Say) (Coleoptera: Scolytidae)

We determined the chirality of ipsdienol in individual male pine engravers,Ips pini (Say), from New York, California, and two localities in British Columbia (BC). Both quantity and chirality of ipsdienol varied significantly between and within populations ofI. pini. Beetles from California and southeastern BC produced primarily (R)-(–)-ipsdienol with mean ratios of (S)-(+) : (R)-(–) of 9 : 91 and 11 : 89, respectively, while beetles from New York produced primarily (S)-(+)-ipsdienol with a mean (S)-(+) : (R)-(–) ratio of 57 : 43. A population from southwestern BC was unlike any other known western population, producing primarily (S)-(+)-ipsdienol with a mean (S)-(+) : (R)-(–) ratio of 66 : 34. In contrast to the unimodal chirality profiles for ipsdienol production in populations from California and southeastern BC, the profiles of the populations from southwestern BC and New York were bimodal, with a common mode at approximately 44 : 56 (S)-(+) : (R)-(–). Bimodality in the profiles of ipsdienol chirality in two populations ofI. pini and remarkably high levels of intrapopulation variation in pheromone chirality in all four populations suggest that evolutionary change in pheromone channels of communication could occur, possibly in response to artificial selection pressures such as mass trapping.     

Pheromone production by axenically rearedDendroctonus ponderosae andIps paraconfusus (Coleoptera: Scolytidae)

Mountain pine beetles,Dendroctonus ponderosae Hopkins, and California five-spined ips,Ips paraconfusus Lanier, were reared axenically from surface-sterilized eggs on aseptic pine phloem. After 24 hr in host logs, axenip femaleD. ponderosae and maleI. paraconfusus produced the aggregation pheromones,trans-verbenol (D. ponderosae), and ipsenol and ipsdienol (I. paraconfusus). Emergent, axenically reared maleD. ponderosae contained normal amounts of the pheromoneexo-brevicomin. Axenic femaleD. ponderosae treated with juvenile hormone or exposed to vapors of -pinene, produced the pheromonetrans-verbenol. By 25–35 days after eclosion, axenic females exposed to -pinene vapors produced over six times as muchtrans-verbenol as wild females, suggesting that while microorganisms in wild females may producetrans-verbenol, they may also inhibit production of the pheromone or use it as a substrate.Research supported in part by Natural Sciences and Engineering Research Council, Canada, Operating Grants A3881 and A3706, and H.R. MacMillan Family Fund Fellowships to J.E. Conn and D.W.A. Hunt.     

Inhibition of the attractant pheromone response inIps pini andI. paraconfusus (Coleoptera: Scolytidae): Field evaluation of ipsenol and linalool

Linalool, a compound from maleI. pini, previously suggested as an inhibitor forI. paraconfusus, has no obvious effect on the response ofI. paraconfusus to ponderosa pine bolts containing maleI. paraconfusus. I. pini from California and New York equally inhibit the response ofI. paraconfusus to maleI. paraconfusus. Ipsenol, one component of the attractant pheromone ofIps paraconfusus, inhibits attacks byIps pini on ponderosa pine logs baited with maleI. pini. The concentration of ipsenol used appears to be critical for effective suppression of attacks.This investigation was supported in part by a grant from the U.S. Forest Service.     

Seasonal variability in response ofIps pini (Coleoptera: Scolytidae) to ipsdienol in New York

In May,Ips pini in New York did not respond in the field to 50–98.5% (R)-(–)-ipsdienol (synthetic). In September, beetles responded strongly to 50–60% (R)-(–)-ipsdienol (synthetic). In May and June, New York beetles showed marked preference for their own males over Arizona males, which produce an average of 94.1% (R)-(–)-ipsdienol. This suggested that ipsdienol stereochemistry alone does not ensure activity and that an additional compound is necessary for attraction in May. In the second year of field tests, attraction to synthetic ipsdienol and male beetles was tested in the spring, summer, and fall. There was response only to males in the spring and mid-summer and to both males and synthetic ipsdienol in the late summer and fall, causing a significant treatment x sampling period (date) interaction. Laboratory-reared beetles were not significantly more attracted to ipsdienol than to a blank airstream in laboratory assays, while male volatiles were significantly more attractive than ipsdienol and the blank. These data demonstrate that there is one or more unknown semiochemicals necessary for pheromonal response and that the behavioral activity of synthetic ipsdienol varies seasonally.Deceased.     

Lanierone: A new pheromone component fromIps pini (Coleoptera: Scolytidae) in New York

A new pheromone component, lanierone, (2-hydroxy-4,4,6-trimethyl-2,5-cyclohexadien-1-one) was isolated and identified from a Porapak Q collection of volatiles from maleIps pini from New York through GC fractionation, bioassay, and spectrometry. In both the laboratory and the field, synthetic lanierone, in a 1:100 ratio with synthetic ipsdienol, is as attractive as natural pheromone sources. Synthetic ipsdienol alone is not attractive in the laboratory and only weakly attractive in the field. Varying the ratio of lanierone to ipsdienol in the field from 10^–41 to 11 in 10-fold increments resulted in an increased number of beetles trapped at the three lower ratios, but also in an increase in the proportion of males trapped. In the field, all combinations of lanierone to ipsdienol attracted proportionately fewer males than did pheromone-producing male beetles. GC and GC-MS analyses of Porapak Q-trapped volatiles revealed that lanierone is produced in an amount equal to about 0.2% of that of ipsdienol and is produced exclusively by males. The small amount of lanierone produced, together with a GC retention time similar to that of ipsdienol on a nonpolar column, probably confounded its detection in earlier studies.Deceased.     

Enantiospecific pheromone production and response profiles for populations of pine engraver,Ips pini (Say) (Coleoptera: Scolytidae), in British Columbia

Analyses of the enantiomeric composition of ipsdienol produced by individual male pine engravers,Ips pini (Say), from six populations in British Columbia, support the hypothesis that New York and Idaho races of this species hybridize in southeastern British Columbia. Production profiles, expressed as frequency distributions of (+):(-) ipsdienol ratios [= ratio of (S)-(+)-ipsdienol to (R)-(-)-ipsdienol], were bimodal for four western British Columbia populations. The (+):(-) ratios ranged from 63:37 to 71:29. consistent with those previously found for the New York race. The profile for a southeastern population from Radium, British Columbia, was intermediate between those for the four western British Columbia populations and that from one population in Kimberley, British Columbia, just south of Radium. Males in the Kimberley population produce predominantly (R)-(-)-ipsdienol, typical of California nad Idaho males. Response profiles of different individuals ofI. pini, determined by captures of beetles in multiple-funnel traps baited with ipsdienol of 11 different (+):(-) ratios, were not consistent with production profiles. Populations in Williams Lake and Princeton, in western British Columbia, and Radium, in southeastern British Columbia, had response profiles with maximal attraction to ipsdienol over a broad range of (+):(-) ratios, falling off as enantiomeric purity was approached at either end of the spectrum. This type of response profile is consistent with that for the New York race, which has been shown to respond optimally to (+):(-) ratios ranging from 40:60 to 70:30. The response profile of the Kimberley population gradually declined from maximal attraction to ipsdienol with a (+):(-) ratio of 2:98 to the lowest response at a (+):(-) ratio of 98:2. The attraction ofI. pini to chemical stimuli in California is interrupted by ipsdienol with a (+):(-) ratio >5:95, a pheromone of a host competitor, the California five-spined ips,Ips paraconfusus Lanier. We hypothesie that the Idaho race, which does not compete withI. paraconfusus due to geographical separation, is characterized by a Kimberley-type enantiomeric response profile, intermediate between those of the New York and California races.     

β-Phellandrene: kairomone for pine engraver,Ips pini (Say) (Coleoptera: Scolytidae)

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 -phellandrene, demonstrating that -phellandrene is a kairomone for this species.Lasconotus complex (Colydiidae) and aCorticeus sp. (Tenebrionidae) were attracted to both ipsdienol and -phellandrene. TheCorticeus sp. exhibited a synergistic response to the combination of ipsdienol and -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 -phellandrene. Attraction of all eight species increased with increasing release rates of ipsdienol and/or -phellandrene.     

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)     

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.     

Methylbutynol effectively replaces methylbutenol,a pheromone component ofIps typographus (L.) (Coleoptera: Scolytidae)

In field experiments in Sweden, the constituent 2-methyl-3-buten-2-ol of the aggregation pheromone of the spruce bark bettleIps typographus (L.) was effectively replaced by 2-methyl-3-butyn-2-ol.     

Effect of juvenile hormone analog,fenoxycarb, on pheromone production byIps paraconfusus (Coleoptera: Scolytidae)

Topical application of the juvenile hormone analog, fenoxycarb, in acetone induced newly emerged male California five-spined ips,Ips paraconfusus Lanier, to become attractive to females, as measured by positive responses to male abdominal extracts in a laboratory bioassay. Two pheromones, ipsdienol and ipsenol, were detected by gas chromatography in the abdominal extracts of fenoxycarb-treated males. Pheromone production was minimal at a dose of 0.1 g/insect of fenoxycarb, maximal at 10 g, and was reduced to unmeasurable amounts at a dose of 100 g. In comparison, peak production of pheromones was induced at a dose of 0.1 g/insect of natural juvenile hormone (JH III). Treatment with 10 g of fenoxycarb resulted in the occurrence of pheromones 12 hr after exposure, maximal pheromone content between 16 and 20 hr, and undetectable amounts after 36 hr. The demonstration that fenoxycarb is an active juvenile hormone analog for a bark beetle suggests that it may have practical utility in managing these insects.     

Attraction of bark beetles (Coleoptera: Scolytidae) to a pheromone trap

The movement of bark beetles near an attractive pheromone source is described in terms of mathematical models of the diffusion type. To test the models, two release experiments involving 47,000 marked spruce bark beetles [Ips typographus (L.)] were performed. The attractive source was a pheromone trap, surrounded by eight concentric rings with eight passive trap stations on each ring. Captures were recorded every 2–10 minutes for the pheromone trap and once for the passive traps. The models were fitted to the distribution in time of the central pheromone trap catch and to the spatial distribution of catch among the passive traps. The first model that gives a reasonable fit consists of two phases: Phase one—After release the beetles move according to a diffusion process with drift towards the pheromone trap. The strength of the drift is inversely proportional to the distance from the traps. Phase two—those beetles attracted to, but not caught by, the pheromone trap are no longer influenced by the pheromone, and their movement is described by a diffusion process without drift. In phase two we work with a loss of beetles, whereas the experiment seems to indicate that the loss of beetles in phase one is negligible. As a second model, the following modification of phase one is considered: After release the beetles move according to a diffusion process without drift, until they start responding to the pheromone (with constant probability per unit time), whereafter they start moving according to a diffusion process with drift. This study, like other release experiments, shows that the efficiency of the pheromone trap is rather low. What is specific for the present investigation is that we try to explain this low efficiency in terms of dynamic models for insect movement. Two factors seem to contribute: Some beetles do not respond to pheromone at all, and some beetles disappear again after having been close to the pheromone trap. It also seems that the motility of the beetles decreased after they ceased responding to the pheromone. Furthermore, the data lend some support to the hypothesis that flight exercise increases the response of the beetles to pheromone.     

Host selection behavior of bark beetles (Coleoptera: Scolytidae) attackingPinus ponderosa,with special emphasis on the western pine beetle,Dendroctonus brevicomis

Detection of weakened hosts from a distance by bark beetles through olfaction was investigated in field experiments. No significant numbers of Scolytidae were attracted to anaerobically treated pine bolts, stem disks, or sugar and ponderosa pine bark including phloem. Treatment of living trees with cacodylic acid induced attacks byDendroctonus brevicomis, D. ponderosae, Ips latidens, Gnathotrichus retusus, andPityophthorus scalptor, beginning two weeks after treatment. There was no significant difference between landing rates ofD. brevicomis andD. ponderosae on screened treated trees and screened controls. There was a significant increase in landing rates ofG. retusus andI. latidens, because both species had penetrated the screen and produced pheromones. Tree frilling alone did not increase the landing rate of bark beetles. Freezing of the lower trunk with dry ice did not increase significantly the landing rate ofD. brevicomis, D. ponderosae, G. retusus, orI. latidens on screened trees, whereas unscreened frozen trees were attacked by all four species. There was no significantly higher landing rate byD. brevicomis, D. ponderosae, I. paraconfusus, I. latidens, G. retusus, orHylurgops subcostulatus on screened trees evidencing symptoms of severe infection by the root pathogenVerticicladiella wagenerii, than on symptornless trees. These experiments show thatD. brevicomis, D. ponderosae, I. paraconfusus, I. latidens, andG. retusus land, apparently indiscriminately, on healthy and stressed hosts. Thus, in these species host discrimination must occur after landing and prior to sustained feeding.These studies were supported in part by the U.S.D.A. Forest Service, Cooperative State Research Services (2598-RRF.W-1 10) and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BM575-04223) to the University of California; and by the Canada Department of the Environment. The findings, opinions and recommendations are not necessarily those of the University of California or the funding agencies.From a thesis submitted by H.A. Moeck to the University of California, Berkeley, in partial fulfillment of the requirements for the degree Doctor of Philosophy in Entomology.     

Ancestral semiochemical attraction persists for adjoining populations of siblingIps bark beetles (Coleoptera: Scolytidae)

Three species ofIps pine bark beetles in Hopping's group IX (S.L. Wood'sgrandicollis group),Ips confusus, I. lecontei, andI. paraconfusus, are parapatrically distributed in the American Southwest. They share post-Pleistocene altitudinal ecotones with their host pines. Adjacent to these areas of host overlap, we tested the hypothesis that aggregation pheromones produced by male beetles and/or host volatiles are sufficient to elicit the speciesspecific colonization behaviors typical of these threeIps species in nature. A more distantly related species,I. pini (Hopping's group IV, S.L. Wood'spini group) was used for outgroup comparison. Under the influence of pheromone, males ofI. confusus andI. paraconfusus do not discern among unin-fested log bolts of host and nonhost pine prior to bark contact. Males responding to pheromones emanating from infested bolts are similarly undiscriminating. Females ofI. confusus andI. lecontei olfactorily discern the combination of conspecific males in host pine from other possible beetlepine combinations; females ofI. paraconfusus do not. FemaleI. pini discerned conspecific pheromone from that ofI. lecontei. The bark beetle predator,Enoclerus lecontei, is attracted by, but does not discriminate among, the male-produced volatiles of these Group IXIps species. These results support a hypothesis that divergence in pheromonal responses by these group IXIps species has evolved following their speciation, having been manifested first in the female sex. Evolutionarily, the derived pheromonal messages have preceded their behavioral discrimination by these beetles. Additional speciesspecific cues may operate between the sexes in the field that may preclude heterospecific pairings.     

The role of lanierone in the chemical ecology ofIps pini (Coleoptera: Scolytidae) in California

Five doses of lanierone (2-hydroxy-4,4,6-trimethyl-2,5-cyclohexadien-1-one) were tested with one dose of enantiomerically pure [99.4% (4R)-(–)] ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) for activity as an aggregation pheromone ofIps pini (Say) in California. The response ofI. pini to 1 mg/day ipsdienol + 20 g/day lanierone was significantly greater than the response to ipsdienol alone, but the response pattern did not demonstrate a clear dose-response relationship. The response to the highest dose of lanierone (2 mg/day) was significantly lower than the response to ipsdienol alone. Ipsdienol attracted significantly moreI. pini than a male-infested log. Lanierone did not alter the percentage of maleI. pini responding to ipsdienol alone. Neither sex ofI. pini orDendroctonus brevicomis LeConte from California produced detectable amounts of lanierone, but myrcene-aerated maleD. brevicomis produced 97.8%-(4S)-(+)-ipsdienol. The black-bellied clerid,Enoclerus lecontei (Wolcott) (Coleoptera: Cleridae) was attracted to lanierone when released with ipsdienol. Neither compound was attractive when released alone, proving synergism for the kairomone of this predator. Lanierone did not influence the response of the predatorsTemnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae) andEnoclerus sphegeus (F.) (Coleoptera: Cleridae), which were attracted to all treatments containing ipsdienol.Tomicobia tibialis Ashmead (Hymenoptera: Pteromalidae) responded in significantly greater numbers to the male-infested log than it did to ipsdienol or ipsdienol + 20 g/day lanierone.     

Improved synthesis ofendo-brevicomin for the control of bark beetles (Coleoptera: Scolytidae)

endo-Brevicomin for testing as pheromone for the control of bark beetles was synthesized in experimental quantities fromtrans-3-hexen-1-ol. Methods used were adapted from procedures for synthesizing ew-brevicomin.Personal communications with Dr. W.D. Bedard, Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Berkeley, California 94701, June, 1973.