Enantiomer-based specificity in pheromone communication by two sympatricGnathoirichus species (Coleoptera: Scolytidae)

The aggregation pheromone ofGnathotrichus retusus was isolated and identified as (S)-(+)-sulcatol (6-methyl-5-hepten-2-ol). In laboratory and field experiments,G. retusus responded to (S)-(+)-sulcatol, but not to (±)-sulcatol, which was attractive to the sympatric species,G. sulcatus. G. sulcatus did not respond to optically pure (S)-(+)-sulcatol, but began to respond when 1% (R)-(–)-sulcatol was present in an enantiomeric mixture.Research supported by the National Science Foundation, U.S.A. (Grant BMS-74-13643), and the Natural Sciences and Engineering Research Council of Canada (Co-op grant A0243 and Operating Grant A3881 and A3785).     

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.     

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.     

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.     

Partial inhibition of pheromone production inDendroctonus ponderosae (Coleoptera: Scolytidae) by polysubstrate monooxygenase inhibitors

Female and male mountain pine beetles,Dendroctonus ponderosae Hopkins, were treated topically with piperonyl butoxide or sesame oil, both of which are known to inhibit poly substrate monooxygenase activity. Beetles then exposed to vapors of the host monoterpenes -pinene and myrcene were found to contain reduced levels of the pheromonestrans-verbenol and ipsdienol, as well as a buildup of monoterpene precursors. Polysubstrate monooxygenase enzymes appear to be at least partially responsible for the detoxification of host monoterpenes and for the production of terpene alcohol pheromones in this species.Research supported in part by Natural Sciences and Engineering Research Council, Canada, Operating Grants A3881 and A7774.     

Interspecific pairing between two siblingIps species (Coleoptera: Scolytidae)

Host and conspecific discrimination were tested as reproductive isolating mechanisms betweenIps paraconfusus Lanier infestingPinus coulteri (Torrey) andI. confusus (Le Conte) infestingP. monophylla (Fremont). In two areas (one area largely Coulter pine and the other largely pinyon pine) where these bark beetles and hosts cooccur in southern California, we induced pheromone production in host and nonhost logs using males of each species.Ips paraconfusus females joined both heterospecific and conspecific males tunneling in both tree species in each area.Ips confusus females failed to joinI. paraconfusus males in Coulter pine, but joinedI. paraconfusus in pinyon pine. Sympatry was demonstrated when females of both sibling species joined conspecific males in their respective hosts. Males attacked all four beetlehost treatment combinations in both areas. Laboratory tests confirmed these results. Males did not displace heterospecific males from nuptial chambers in hosts, and they did not occupy a gallery in which heterospecific males produced frass. Females that left conspecific males in a host were readily accepted by heterospecific males and oviposited in a nonhost.     

Electroantennogram responses of two populations ofIps pini (Coleoptera: Scolytidae) to insect-produced and host tree compounds

Electroantennograms in two populations ofIps pini (Idaho and New York) were very similar, even though previous work documented behavioral specificity and revealed that the populations produce different ratios of the enantiomers of the aggregating pheromone ipsdienol. The insect- and host-produced compounds tested evoked characteristic response curves in both populations. EAG amplitude was highest to ipsdienol and the aggregation inhibitor ipsenol. Among the other compounds tested, responses were generally higher to the beetle-produced odorants (linalool, verbenone,trans-verbenol) than to host terpenes (1-octanol, -pinene). The antennal club and its sensory receptors are described and illustrated by scanning electron micrographs.From a thesis presented in partial fulfillment of the degree Master of Science. Department of Environmental and Forest Biology, SUNY College of Environmental Science and Forestry, Syracuse, New York 13210     

(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.     

Pheromone receptor cell specificity in interpopulational hybrids ofIps pini (Coleoptera: Scolytidae)

Electrophysiological studies of pheromone receptor cells keyed to ispdienol were performed in laboratory-raised hybrids of the eastern and western populations of the pine engraver,Ips pini. As previously shown in the parental beetles, the receptor cells keyed to ipsdienol could be classified as two distinct types: one keyed to (+)- and one to (–)-ipsdienol. None of the 20 ipsdienol cells recorded from F₁ hybrids were of an intermediate type. Recordings of the summated receptor responses (EAGs) showed no significant difference between parental beetles and hybrids. Similar results were obtained in reciprocal crosses, eastern females with western males and the reverse. Thus, there was no indication that sex-linked alleles determined the specificity of the ipsdienol receptor cell. The ratio between (+) and (–) cells was 146 in the hybrids compared to 112 in the western and 912 in the eastern populations.     

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.     

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.     

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.     

Structure-activity studies on aggregation pheromone components ofPityogenes chalcographus (Coleoptera: Scolytidae)

Syntheses of all four Stereoisomers (2S,5S; 2S,5R;2R,5R; and2R,5S) of chalcogran, a major component of the aggregation pheromone ofPityogenes chalcographus, and of all four isomers (2Z,4Z; 2Z,4E; 2E,4E; and 2E,4Z) of methyl 2,4-decadienoate (MD), the second major pheromone component, are briefly described. Attraction responses of walking beetles of both sexes were tested to mixtures of the synergistic pheromone components or analogs. These bioassays showed that theE,Z isomer of MD is the most active when tested with chalcogran. When tested with (E,Z)-MD, (2S,5R)-chalcogran was the most active stereoisomer, while 2R,5R and 2R,5S isomers had intermediate activities, and the 2S,5S isomer was inactive. There was no evidence that the relatively less active Stereoisomers of chalcogran inhibited or promoted attraction to (2S,5R)-chalcogran with (E,Z)-MD. Male beetles only produce the activeE,Z isomer of MD (inactive alone) and their hindguts contain the most active (2S,5R)- and least active (2S,5S)-chalcogran. A mixture of all MD isomers with racemic chalcogran was not significantly different in attractivity compared to (E,Z)-MD with racemic chalcogran, indicating no synergistic or inhibitory effects of the inactive isomers of MD.     

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.     

Receptor discrimination of enantiomers of the aggregation pheromone ipsdienol,in two species ofIps

The stimulation effect of the two enantiomers of the male-produced aggregation pheromone, ipsdienol, was tested by electrophysiological recordings from single olfactory cells in females of two species,Ips pini andI. paraconfusus. The results demonstrated two types of receptor cells, each specialized to one of the optical configurations. This suggests that separate acceptors (membrane receptors) for (+)- and (–)-ipsdienol are produced by the beetles' receptor cells. The dose-response curves obtained for the 92% pure enantiomers and racemic mixtures indicated no synergistic or inhibitory interaction of the enantiomers on the receptor cells. The results could be explained by activation of one acceptor type in each cell group. I. paraconfusus apparently had the majority of its ipsdienol cells keyed to the (+)-enantiomer. Conversely, the westernI.pini had more cells tuned to (–)- than to (+)-ipsdienol. This difference is consistent with behavioral responses where these species are sympatric in California. The (+)- and (–)-ipsdienol are aggregation pheromone components ofI. paraconfusus anaI. pint, respectively, and the opposite enantiomers act as aggregation inhibiting allomones. More (–)- than (+)-ipsdienol cells were also obtained in the easternI. pint, even though this population produces more (+)- than (–)-ipsdienol (6335) and requires both enantiomers for aggregation behavior. However, the difference in the numbers of (+)- and (–)-ipsdienol cells recorded from the eastern population was insufficient for an acceptable level of statistical confidence.     

Collection on Porapak Q of the aggregation pheromone ofScolytus multistriatus (Coleoptera: Scolytidae)

The attractive volatiles in the air around the virgin female of the smaller European elm bark beetle,Scolytus multistriatus (Marsham), tunneling in elm logs can be collected by passing the air through a column of Porapak Q. These volatiles can be removed from the Porapak by Soxhlet extraction with hexane, yielding an extract that is attractive to in-flight beetles in the field. GLC analyses of this extract and an extract of virgin female frass indicate that the aeration extract contains active chemicals that are not in the extract of frass.     

Geometrical and optical isomerism of pheromones in two sympatricDryocoetes species (Coleoptera: Scolytidae), mediates species specificity and response level

In a field-trapping experiment, western balsam bark beetles,Dryocoetes confusus Swaine, were highly attracted to a 51 mixture of (±)-exo-and (±)-endo-brevicomin. Beetles in the sympatric speciesD. affaber (Mann.), were best attracted to a 11 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 91 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.During the course of the research, A.D. Camacho was on educational leave from the Escuela Nacional de Ciencias Biológicas. I.P.N. Depto. de Zoología. Prol. Carpio y Plan de Ayala, Mexico 11340D.F. México.     

Specificity of response to pheromones in the genusIps (Coleoptera: Scolytidae)

Seventeen species ofIps were laboratory or field tested for the specificity of their response to male-produced aggregating pheromones. In the laboratory, some species appeared not to differentiate among their own pheromones and those of closely related species, whether the pheromones were bioassayed individually or in direct competition. Other species showed strong preference for their own pheromones in competition with those of closely related species, even though they had demonstrated strong attraction to pheromones of the related species. Cross-responsiveness amongI. confusus, I. montanus, andI. paraconfusus, and betweenI. mexicanus andI. concinnus, was confirmed in field tests. Moreover, wildI. paraconfusus females entered the nuptial chambers of males ofI. montanus andI. confusus but not those of the more distantly relatedI. mexicanus. It is hypothesized that specificity of response to aggregating pheromone is important in the maintenance of reproductive isolation among sympatricIps and that the lack of specificity among closely related species enforces the parapatric distributions characteristic of these species.     

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.     

Synthesis and field testing of 4,6,6-lineatin,the aggregation pheromone ofTrypodendron lineatum (Coleoptera: Scolytidae)

Authentic 4,6,6-lineatin (3,3,7-trimethyl-2,9-dioxatricyclo-[3.3.1.0^4,7]nonane) (I) was produced in low yield via three synthetic pathways. In field tests, microgram amounts of the product from all three syntheses attracted large numbers ofTrypodendron lineatum of both sexes. These results confirm that 4,6,6-lineatin (I) is a population aggregation pheromone forT. lineatum.Research supported by National Science Foundation (U.S.A), Grant PCM4-13643, National Research Council (Canada), Co-op Grant A0243 and Operating Grants A3881 and A3785, and a Canadian Forestry Service Science Subvention Grant.