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.     

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.     

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.     

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.     

Receptor cells inIps typographus andDendroctonus micans specific to pheromones of the reciprocal genus

Olfactory receptor cells were studied electrophysiologically inIps typographus andDendroctonus micans. The investigation revealed cells which were keyed to pheromone compounds characteristic of the reciprocal genus. Thus, cells keyed toexo-brevicomin were found inI. typographus, whereas cells keyed to (+)-ipsdienol were present inD. micans. Laboratory behavioral tests indicated an attractive effect of the two compounds on beetles of the reciprocal genus. InI. typographus the effect ofexo-brevicomin predominantly concerned males and enhanced their response to the pheromone ipslure. It is suggested thatexo-brevicomin serves as an interspecific attractant forI. typographus, which may be guided by pheromone compounds of the reciprocal genus in finding suitable breeding material. The function of (+)-ipsdienol inD. micans is more uncertain. It may be either a pheromone or an interspecific messenger.     

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.     

IPS pini: The basis for interpopulational differences in pheromone biology

Ips pini from Idaho (ID) produce (–)-ipsdienol and respond to it in the laboratory.I. pini from New York (NY) produce (+) and (–)-ipsdienol in a 6535 ratio and respond much more strongly to the (+) than to the (–) enantiomer. Response byI. pini-ID to (–)-ipsdienol in the laboratory was inhibited by (+)-ipsdienol, while the field response byI. pini-NY was optimal to a 50:50 mixture of (+) and (–)-ipsdienol. This differential production and response to enantiomers of ipsdienol is sufficient to account for populational specificity observed in earlier experiments and confirmed by our current work. Reciprocal hybrids of the NY and IDI. pini populations did not differ in their patterns of attraction and response; those of both types of F₁ were similar to NY beetles. Thus, it appears that (+)-ipsdienol is produced by the hybrids and is necessary for their maximum response, but this supposition was not tested. The genes controlling the pheromone biology ofI. pini are not sex linked. Since previous whole-antenna and single-cell electrophysiological data show that the receptor systems of the two populations are virtually identical, response behavior seems to be governed by the central nervous system rather than by the characteristics of the olfactory receptors.Coleoptera: Scolytidae.Supported by grants from the Rockefeller Institute, the National Science Foundation, and the Research Foundation of Providence, Rhode Island.     

Disruption of Secondary Attraction of the Spruce Beetle, Dendroctonus rufipennis, by Pheromones of Two Sympatric Species

Capture of spruce beetles, Dendroctonus rufipennis, in multiple-funnel traps baited with frontalin and -pinene was reduced by up to 42% in the presence of synthetic (+)-exo- and (+)-endo-brevicomin, aggregation pheromones of the sympatric species Dryocoeles affaber. (±)-endo-Brevicomin was inhibitory to spruce beetles in two experiments and (±)-exo-brevicomin was inhibitory in one experiment, reducing spruce beetle trap catches by up to 87% and 75%, respectively. Spruce beetle trap catches were also reduced by 85% by (±)- or (+)-ipsdienol, but not by (–)-ipsdienol. Ips tridens, a second sympatric species, produces both enantiomers of ipsdienol in its pheromone blend. Responses by D. affaber to its own pheromone were significantly enhanced by addition of the spruce beetle lure. Enantiospecific pheromones of secondary competing species, or less costly racemic substitutes, may be useful for managing spruce beetles using competitive displacement or exclusion. Baiting susceptible hosts with pheromones of secondary species may enhance attack by secondary species, while partially repelling spruce beetles.     

Aggregation Pheromone of Pityogenes knechteliand Semiochemical-Based Interactions with Three Other Bark Beetles

Gas chromatographic–electroantennographic detection and GC-mass spectrometric analyses of volatile extracts from male and female Pityogenes knechteli Swaine identified hexanol, (±)-ipsdienol, and (S)-(–)-ipsenol as male-produced candidate pheromone components. In a lodgepole pine, Pinus contorta var. latifolia Engelmann, forest in the southern interior of British Columbia, multiple-funnel traps baited with (±)-ipsdienol alone, (S)-(–)-ipsenol alone, or both caught 60%, 6%, and 23%, respectively, of all P. knechteli trapped; unbaited traps caught the remaining 11%. In another field trapping experiment, (S)-(+)-ipsdienol was as attractive as (±)-ipsdienol, and (R)-(–)-ipsdienol was behaviorally benign. (S)-(+)-Ipsdienol is thus concluded to be the principal aggregation pheromone component of P. knechteli. At low release rates, hexanol increased attraction of beetles to (±)-ipsdienol, or to (±)-ipsidienol plus (S)-(–)-ipsenol, but at high release rates hexanol decreased attraction, suggesting a role in preventing overpopulation in the host tree. On the basis of laboratory bioassays in which walking beetles were attracted to (S)-(–)-ipsenol, we hypothesize that (S)-(–)-ipsenol serves as a short-range attractant for P. knechteli. Three sympatric scolytids were also captured in field experiments as follows: the pine engraver, Ips pini (Say), to its pheromone (±)-ipsdienol; I. latidens LeConte to its pheromone (S)-(–)-ipsenol; and I. mexicanus (Hopkins), for which the pheromone is unknown, to (S)-(–)-ipsenol with (±)-ipsdienol. Although all four species attack lodgepole pine, we have never observed I. latidens or I. mexicanus attacking the same hosts at P. knechteli or I. pini. These results suggest that ipsenol and ipsdienol serve as synomones involved in promoting aggregation on the host tree, maintaining species-specific communication, and thus contributing to resource partitioning and reduced competition among the four species.     

Myrcene Hydroxylases do not Determine Enantiomeric Composition of Pheromonal Ipsdienol in <Emphasis Type="Italic">Ips</Emphasis> spp.

Myrcene (7-methyl-3-methylene-1,6-octadiene) hydroxylation is likely one of the final reactions involved in the production of the Ips spp. (Coleoptera: Scolytidae) aggregation pheromone components, ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) and ipsenol (2-methyl-6-methylene-7-octen-4-ol). To gain insight into the evolution of pheromone production, we isolated a full-length cDNA from the pinyon ips, Ips confusus (LeConte), that encodes a pheromone-biosynthetic cytochrome P450, I. confusus CYP9T1 (IcCYP9T1). The recovered cDNA is 1.70 kb, and the open reading frame encodes a 532 amino acid protein. IcCYP9T1 is 94% identical to the pine engraver, Ips pini (Say), CYP9T2 ortholog that hydroxylates myrcene. Quantitative real-time PCR experiments showed that IcCYP9T1, as does CYP9T2, has an expression pattern similar to other pheromone-biosynthetic genes in I. pini. Basal expression levels were higher in males than females, and expression was significantly induced in male, but not in female, anterior midguts by feeding on host phloem. Microsomes, prepared from Sf9 cells co-expressing baculoviral-mediated recombinant IcCYP9T1 and house fly (Musca domestica) NADPH-cytochrome P450 reductase, converted myrcene to ~85%-(R)-(−)-ipsdienol. These results are consistent with IcCYP9T1 encoding a myrcene hydroxylase that functions near the end of the pheromone-biosynthetic pathway. Since the I. confusus pheromone blend contains >90%-(S)-(+)-ipsdienol, these results confirm further that Ips spp. myrcene hydroxylases do not control the final ipsdienol enantiomeric blend. Other enzymes are required following myrcene hydroxylation to achieve the critical quantity and enantiomeric composition of pheromonal ipsenol and ipsdienol used by different Ips spp. Sequences The IcCYP9T1 cDNA sequence has been deposited in Genbank, accession number EU915209     

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.)     

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)     

Production of pheromone by hairpencil glands of males obtained from interspecific hybridization betweenHeliothis virescens andH. subflexa (Lepidoptera: Noctuidae)

Pheromone produced by the hairpencil glands of interspecific hybrid- and backcross-generation males from crosses betweenHeliothis virescens (F.) withH. subflexa (Gn.) was studied. Males of reciprocal F₁ hybrids, all of which had hairpencil glands morphologically similar to those ofH. virescens, produced neither the same pheromone blend nor amounts of pheromone that were produced by males ofH. virescens. Instead, these hybrid males produced pheromone that was quantitatively and qualitatively similar to that produced byH. subflexa. Hairpencil gland extracts from males obtained from backcrossing F₁ females of either cross to males ofH. subflexa were the same as those ofH. subflexa. However, extracts from backcross males of crosses between F₁ females andH. virescens were variable. Some extracts from these backcross males were like those ofH. virescens while others were either likeH. subflexa or were intermediate between those of the parent species. These results showed that the production of pheromone by the hairpencil glands of hybrid and backcross males is under the dominant regulation of autosomal genes of theH. subflexa genome.     

Reproductive Character Displacement in Lymantria monacha from Northern Japan?

Our objective was to test the hypothesis that the pheromone blend and/or diel periodicity of pheromonal communication differ in populations of the nun moth, Lymantria monacha(Lepidoptera: Lymantriidae), from eastern Asia (northern Honshu, Japan) and Central Europe (Bohemia, Czech Republic). Coupled gas chromatographic–electroantennographic detection (GC-EAD) analyses of pheromone gland extract of female L. monachafrom Japan confirmed the presence of compounds previously identified in pheromone extracts of L. monachafrom Bohemia, as follows: (Z)-7-octadecene, 2-methyl-(Z)-7-octadecene (2me-Z7–18Hy), cis-7,8-epoxy-octadecane (monachalure), and cis-7,8-epoxy-2-methyloctadecane (disparlure). Field experiments in Honshu suggested that (+)-monachalure is the major pheromone component of L. monacha. 2me-Z7–18Hy significantly enhanced attractiveness of (+)-monachalure. Addition of (+)-disparlure to (+)-monachalure plus 2me-Z7–18Hy in Honshu and Bohemia increased attractiveness of lures by 1.2 and 20 times, respectively, indicating that (+)-disparlure is of least and most significance in the respective L. monachapopulations. Moreover, capture of male L. monachain pheromone-baited traps between 18:00 and 24:00 hr in Bohemia and 2:00 and 5:00 hr in Honshu revealed a markedly different diel periodicity of pheromonal communication. Pheromonal communication late at night and use of (+)-monachalure, rather than (+)-disparlure, as the major pheromone component by L. monachain Honshu may have resulted from interspecific competition with coseasonal L. fumida, which uses the early night for pheromonal communication and (+)-disparlure as major pheromone component. Whether communication channel divergence of L. monachain Honshu indeed constitutes a case of reproductive character displacement is difficult to prove. The evolution of such divergence in sympatricpopulations of L. fumidaand L. monachawould have to be demonstrated.     

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.     

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.     

(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.     

Aggregation pheromones inDryocoetes affaber (Mann.) (Coleoptera: Scolytidae): stereoisomerism and species specificity

Chemical analysis of whole body extracts and volatiles produced by feeding malesDryocoetes affaber (Mann.) disclosed (+)-exo-brevicomin and (+)-endo-brevicomin [(+)EXOB and (+)ENDOB], as the major insect-produced potential pheromones. Laboratory bioassays and field-trapping experiments demonstrated that (+)ENDOB is the main pheromone component, and (-)ENDOB has an inhibiting effect. EXOB either as (+) or (±) appears to be a multifunctional pheromone. It has a synergistic effect in blends of EXOB and ENDOB in ratios up to 1:1, and it is inhibitory at higher ratios. (-)EXOB was inactive. The most attractive blend forD. affaber was a 1:2 blend of (+)EXOB and (+)ENDOB. When this blend was compared with a 9:1 blend, the best known blend forDryocoetes confusus Swaine, the responses by beetles of each of the two species were highly specific, providing evidence for pheromonal exclusion between the two congenerics. We conclude that the combined effect of chirality and the ratio of geometrical isomers of brevicomin determines both the level of response and the species-specificity of the chemical signal inD. affaber.On educational leave from the Escuela Nacional de Ciencias Biológicas. I.P.N. Depto. de Zoología, Prol. Carpio y Plan de Ayala, México 11340 D.F. México.     

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.     

(7R,8S)-cis-7,8-epoxy-2-methyloctadec-17-ene: a novel trace component from the sex pheromone gland of gypsy moth, Lymantria dispar

Considering the vast Eurasian distribution of gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae), the many subspecies, and their presence in different lymantriid communities, we tested the hypothesis that L. dispar populations in eastern Asia employ one or more pheromone components in addition to the previously known single component pheromone (7R,8S)-cis-7,8-epoxy-2-methyloctadecane [= (+)-disparlure]. Coupled gas chromatographic–electroantennographic detection (GC–EAD) analyses of pheromone gland extracts of female L. dispar sensu lato (including both AGM and NAGM) on four GC columns (DB-5, DB-23, DB-210, and SP-1000) revealed a new trace component that eluted just before (DB-5; DB-210) or after (DB-23, SP-1000) disparlure, and elicited strong antennal responses. Isolation of this compound by high-performance liquid chromatography and hydrogenation produced disparlure, suggesting that the new component had the molecular skeleton of disparlure, with one or more double bonds. Of all possible monounsaturated cis-7,8-epoxy-2-methyloctadecenes, only cis-7,8-epoxy-2-methyloctadec-17-ene co-chro- matographed with the insect-produced compound on all GC columns and elicited comparable antennal responses. In field experiments in Honshu (Japan) with enantioselectively synthesized compounds, (7R,8S)-cis-7,8-epoxy-2- methyloctadec-17-ene (7R8S-epo-2me-17-ene-18Hy) was weakly attractive to male L. dispar, but was less effective as a trap bait than (+)-disparlure, and failed to enhance attractiveness of (+)-disparlure when tested in blends. The antipode, (7S,8R)-cis-7,8-epoxy-2-methyloctadec-17-ene, was not attractive, and when added to (+)-disparlure and/or 7R8S-epo-2me-17-ene-18Hy reduced attractiveness. Thus, the biological role of 7R8S-epo-2me-17-ene-18Hy remains unclear. It may enhance pheromone attractiveness or specificity in other L. dispar populations within their vast Eurasian distribution.