The response of mountain pine beetle (Dendroctonus ponderosae) to lodgepole pine trees baited with verbenone and exo-brevicomin

exo-brevicomin, a multifunctional pheromone of the mountain pine beetle,Dendroctonus ponderosae, was tested at release rates of 0.5 and 2.5 mg/day alone and in combination with the antiaggregation pheromone verbenone against unbaited controls. Significantly more lodgepole pinePinus contorta var.latifolia trees were attacked, and at higher densities, with both release rates ofexo-brevicomin than with all other treatments. Verbenone significantly reduced the response of mountain pine beetles toexo-brevicomin. Verbenone alone did not reduce the number of trees attacked by mountain pine beetle or the attack density when compared to the unbaited controls.     

Green leaf volatiles as antiaggregants for the mountain pine beetle,Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae)

We tested the hypothesis that green leaf volatiles act as antiaggregants for the mountain pine beetle (MPB),Dendroctonus ponderosac Hopkins. In coupled gas chromatographic-electroantennographic detection (GC-EAD) analysis MPB antennae responded to 30 ng doses of all six-carbon green leaf alcohols tested [1-hexanol, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol, (E)-3-hexen-1-ol, and (Z)-3-hexen-1-ol], but not to the aldehydes, hexanal or (E)-2-hexenal, or to alcohol or aldehyde homologues with more or fewer than six carbon atoms. In field trapping experiments a blend of green leaf alcohols [1-hexanol, (Z)-2-hexen-1-ol, (E)-3-hexen-1-ol and (Z)-3-hexen-1-ol] effectively disrupted the response to attractive semiochemicals; a blend of the aldehydes hexanal and (E)-2-hexenal was inactive. The two best disruptants. (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol, reduced catches of both sexes to levels not significantly different from catches in unbaited control traps. They also reduced the attack on trees baited with attractive MBP pheromones to a level not significantly different from that on unbaited control trees. Neither of the clerid predators captured,Enoclerus sphegeus (F.) norThanasimus undatulus (Say), was repelled by green leaf volatiles. Our results suggest that green leaf alcohols are promising disruptants which may be used to supplement the antiaggregation pheromone, verbenone, in protecting single high-value trees as well as carefully selected stands with low-level populations of MPBs.     

Electroantennogram responses by mountain pine beetles,Dendroctonus ponderosae Hopkins,exposed to selected semiochemicals

Electroantennograms (EAGs) were obtained forD. ponderosae to the bark beetle pheromonestrans-verbenol,cis-verbenol,exo-brevicomin,endo-brevicomin, frontalin, verbenone; to the kairomones, -pinene, -pinene, camphene, -3-carene, limonene, myrcene; to a blend (111) oftrans-verbenol,exo-brevicomin, and myrcene; and to diacetone-alcohol. Male and female responses, in general, did not differ significantly over the whole EAG dose-response curves but differed at a few concentrations on many of the curves. There were more differences noted for pheromones than kairomones. The blend yielded among the largest EAGs in both sexes and appeared to show synergism. Responses of females were lower than those for males in most instances. Significant differences in responses by the two sexes were much fewer for the kairomones than the pheromones. EAG recovery rates tested at only one concentration showed significant differences between males and females for three pheromones,trans-verbenol,cis-verbenol, and verbenone, and two kairomones, camphene and -3-carene. Thresholds were quite low for most of the odorants exceptcis-verbenol, camphene, verbenone, and diacetone-alcohol in females, andcis-verbenol, verbenone, -pinene, and diacetone-alcohol in males. The results, using at least one EAG parameter, support behavioral and field studies involvingexo-brevicomin,trans-verbenol, frontalin, and the blend.     

Electroantennograms by mountain pine beetles,Dendroctonus ponderosae Hopkins,exposed to selected chiral semiochemicals

Electroantennograms (EAGs) were recorded fromD. ponderosae to the enantiomers of the terpenoid bark-beetle pheromonestrans-verbenol,cis-verbenol, verbenone, and the bicyclic ketals frontalin,exo-brevicomin, andendo-brevicomin. Male and female responses to enantiomers of the terpenoids differed significantly only at the two highest concentrations. No sex differences were seen in response to the bicyclic ketals. Significantly different responses to the enantiomers of all the chemicals, except frontalin, were noted over at least part of the dosage-response ranges tested. The negative antipode for all of the terpenoids elicited higher responses, while for the bicyclic ketals, the positive antipode effected the largest responses except for the two highest concentrations ofexo-brevicomin.     

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)     

Monoterpene metabolism in female mountain pine beetles,Dendroctonus ponderosae Hopkins,attacking ponderosa pine

Abdominal volatiles of female mountain pine beetles,Dendroctonus ponderosae Hopkins, fed in ponderosa pine,Pinus ponderosa Dougl. ex Laws, and in lodgepole pine,P. contorta var.latifolia Engelmann, were analyzed by gas chromatography and coupled gas chromatography-mass spectrometry and were found to comprise host oleoresin components and beetle-produced alliylic alcohols, aldehydes, and ketones derived from host monoterpenes. Neitherexo- andendo-brevicomin nor frontalin were detected. Three metabolic pathways are proposed to account for the distribution of beetle-produced monoterpene alcohols. The first pathway involves hydroxylation of monoterpene substrates on allylic methyl groups which areE to a methylene or vinyl group. This oxidation pathway is indiscriminate with respect to substrate and probably functions to detoxify monoterpenes. A second pathway, which hydroxylates theendo-cyclic methyleneE to a vinyl methyl group of bicyclic monoterpenes to give almost exclusively thetrans alcohol, is hypothesized to be involved in pheromone production. A third detoxification pathway involves anti-Markovnikov addition of water to theexo-cyclic double bond of -phellandrene to give predominantlytrans-2-p-menthen-7-ol.Coleoptera: Scolytidae.Research supported by the Natural Sciences and Engineering Research Council of Canada: Operating Grant A3881 and A3706; Strategic Grant G1039; and Science Council of British Columbia Grant 33 (RC-4).     

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

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

Sex-specific production of ipsdienol and myrcenol byDendroctonus ponderosae (Coleoptera: Scolytidae) exposed to myrcene vapors

Male mountain pine beetles,Dendroctonus ponderosae Hopkins, produced ipsdienol [97.0% ± 0.3S-(+)] and myrcenol (90.3% ± 4.0E) when exposed to myrcene vapors. Females which were exposed to myrcene vapors did not produce any ipsdienol, but did produce low levels of myrcenol (98.0% ± 0.7E). Neither sex produced detectable levels of ipsdienol or myrcenol when fed for 24 hr on lodgepole pine,Pinus contorta var.latifolia Engelmann. The sex-specific conversion of myrcene to ipsdienol and myrcenol suggests that these compounds may have behavioral significance within the species. In addition, the S-(+)-ipsdienol produced by maleD. ponderosae probably functions as a repellent allomone againstIps pini (Say).Research supported in part by Natural Sciences and Engineering Research Council, Canada, Operating Grants A3881, A3785 and A0851, Strategic Grant G1039, and a Postgraduate Scholarship to D.W.A. Hunt.     

Response ofDendroctonus brevicomis andIps paraconfusus (Coleoptera: Scolytidae) to combinations of synthetic pheromone attractants and inhibitors verbenone and ipsdienol

DendroctonusBrevicomis andIps paraconfusus are sympatric bark beetle species colonizingPinus ponderosa in western North America. Interspecific and intraspecific competition for resources is, in part, mediated through semiochemicals. The response ofD. brevicomis to its attractant pheromone was significantly reduced by simultaneous release of either verbenone or racemic ipsdienol. Trap catch was significantly further reduced by including both inhibitors with the attractant pheromones. However, although the response ofIps paraconfusus was significantly inhibited with the addition of either verbenone or racemic ipsdienol, both compounds together did not result in a significant further reduction in trap catch. There was a trend for greater reduction in response ofD. brevicomis to attractant pheromones with increased release rates of either 69% (+)-/31% (–)-verbenone or 84% (–)-/16% (+)-verbenone. Response of associates to attractants and inhibitor combinations was also determined.     

Determining release rates of 3-methyl-2-cyclohexen-1-one antiaggregation pheromone ofDendroctonus pseudotsugae (Coleoptera:Scolytidae)

A method of analysis using high-pressure liquid chromatography (HPLC) with an ultraviolet detector was developed for determining release rates of the antiaggregation pheromone ofDendroctonus pseudotsugae Hopkins, 3-methyl-2-cyclohexen-1-one (MCH), in controlled-release formulations. The pheromone released by the formulations was swept from the test apparatus, trapped on Porapak-QS packing, and eluted with solvent. Aliquots of the eluate were analyzed by liquid chromatography. Release rates of 5–400 g MCH/hr per g formulation were determined from 5-g samples of the controlled-release formulations.     

Response ofDendroctonus brevicomis Le Conte (Coleoptera: Scolytidae) to different release rates and ratios of aggregation semiochemicals and the inhibitors verbenone and ipsdienol

The response of western pine beetle,Dendroctonus brevicomis Le Conte, to different release rates of the aggregation semiochemicals (attractants)exo-brevicomin, frontalin, and myrcene and the inhibitors verbenone and ipsdienol was investigated. Release rates of verbenone ranging from 0.18 mg/ 24 hr to 1.2 mg/24 hr did not result in significant reductions in mean trap catch ofD. brevicomis. In contrast, very low release rates of ipsdienol (0.02–0.4 mg/24 hr) significantly reduced trap catch compared to controls. The combination of verbenone and ipsdienol, released at rates above 0.09 and 0.02 mg/24 hr, respectively, resulted in significantly lower trap catches ofD. brevicomis in attractant-baited traps. Results of an experiment testing a factorial combination of different release rates of verbenone and attractants suggest that response is not ratio-specific. The response curve ofD. brevicomis to the levels of verbenone was similar across all levels of attractants, while the response to equivalent ratios of attractants to verbenone was not similar, suggesting that the behavior of the beetles is primarily influenced by the absolute release rate of verbenone.     

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.     

Southern pine beetle: Olfactory receptor and behavior discrimination of enantiomers of the attractant pheromone frontalin

In laboratory and field bioassays, the response ofDendroctonus frontalis was significantly greater to the mixture of (1S, 5R)-(–)-frontalin andalpha-pinene than to (1R,5S)-(+)-frontalin andalpfa-pinene. Electro-physiological studies revealed that antennal olfactory receptor cells were significantly more responsive to (1S, 5R)-(–)-frontalin than to (1R, 5S)-(+)-frontalin. Both enantiomers stimulated the same olfactory cells which suggests that each cell possesses at least two types of enantiomer-specific acceptors.Texas Agricultural Experiment Station paper no. 14496. The work was funded in part by McIntire-Stennis project 1525 (TAES) and the USDA program entitled The Expanded Southern Pine Beetle Research and Applications Program through TAES-CSRS grant 680-15-10. The findings, opinions, and recommendations reported herein are those of the authors and not necessarily those of the United States Department of Agriculture.     

Influence of aggregation inhibitors (verbenone and ipsidenol) on landing and attack behavior ofDendroctonus brevicomis (Coleoptera: Scolytidae)

The influence of the aggregation inhibitors verbenone and ipsdienol on the response of western pine beetle,Dendroctonus brevicomis, to attractive host trees was investigated. Paired ponderosa pine trees (Pinus ponderosa) were baited with aggregation semiochemicals to stimulate mass attack. One tree in each pair received an inhibitor treatment consisting of five sets of two verbenone and two ipsdienol dispensers spaced 1 m apart vertically along the tree bole. Beetle landing was monitored with sticky traps on the tree bole, and attack density was assessed from bark samples removed four or seven days after baiting. The inhibitor treatment resulted in a significant reduction of both the numbers of beetles landing on trees and the density of attacking beetles compared to control trees (without inhibitors). The ratios of beetle landing density to attacking density were not different between inhibitor-treated and control trees, nor were the vertical distributions of beetles landing or attacking, suggesting that beetle behavior was primarily influenced at a longer range, prior to landing on the tree. Although the application of verbenone and ipsdienol did not preventD. brevicomis from attacking baited trees, our results suggest that when applied to unattacked (and unbaited) trees, their effectiveness at reducing the attack pressure might allow trees having a certain amount of resistance to survive attack by pioneer beetles.     

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.     

Frontalin in the male mountain pine beetle

Frontalin andexo-brevicomin were identified by GC-MS in air drawn over maleDendroclonus ponderosae Hopk. (MPB) from Oregon that had joined females for 1–2 days in the bark of lodgepole and ponderosa pine logs. Unfed males releasedexo- andendo-brevicomin but not frontalin. These three compounds were not detected in either unfed or fed females. Arrestment of males bytrans-verbenol and terpenes in an olfactory walkway was reduced by the addition of racemic frontalin; production of attractant chirps also diminished. Racemic frontalin also strongly reduced the aggregation of MPB in lodgepole and ponderosa pine stands to sticky traps baited with the aggregation pheromonetrans-verbenol and host terpenes; however, the function of the natural enantiomer of frontalin in MPB is unknown.Research supported by NSF Grant PCN 79-21708. O.S.U. Agricultural Experiment Station Technical Paper No. 6219.     

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.     

Dendroctonus pseudotsugae hopkins (Coleoptera: Scolytidae): Production of and response to enantiomers of 1-methylcyclohex-2-en-1-ol

Female Douglas-fir beetles,Dendroctonus pseudotsugae, produced an average 4555 mixture of the (S)-(–)- and (R)-(+)-enantiomers of 1-methylcyclohex-2-en-1-ol (MCOL). The (S)-(–)(R)-(+) ratio of 3-methylcyclohex-2-en-1-ol (seudenol) produced by this population of females was 3466. Lindgren funnel traps baited with (R)-(+)-MCOL attracted significantly more males and females than (S)-(–)-MCOL-baited traps, which captured significantly more beetles than unbaited controls. The combined effect of the enantiomers was additive, rather than synergistic. Either enantiomer of MCOL increased catches by frontalin-baited traps. Racemic MCOL can be used for trapping Douglas-fir beetles in south-central British Columbia.     

Single cell responses of the Douglas-fir beetle,Dendroctonus pseudotsugae hopkins (Coleoptera: Scolytidae), to pheromones and host odors

Olfactory perception of pheromones and host odors byDendroctonus pseudotsugae males and females was investigated through single cell recordings. Responses of 71 cells (35 cells in males; 36 cells in females) were recorded to 1 g of 10 pheromones and three host terpenes. The olfactory cells were classified into four types based on sensitivity and specificity for the various odors: (1) 3,2-MCHone (3-methyl-2-cyclohexenone) cells; (2) 3,2-MCHol (3-methyl-2-cyclohexenol) cells; (3) frontalin cells; and (4) synergist cells. 3,2-MCHone and 3,2-MCHol cells in both males and females were the most sensitive and specific of all cells recorded with a threshold ca. 0.001–0.01 g on filter paper. Frontalin cells were less specialized than the two aforementioned cell types and had a somewhat higher threshold of ca. 0.01 g. A larger percentage of these three cell types were recorded in males than in females. The synergist cells had the highest threshold of all recorded cell types and were the least specific. Each of these cells was most responsive to eithercis-verbenol,trans-verbenol, 1,2-MCHol, verbenone, -pinene, or limonene; however, responses could be elicited by stimulation with other pheromones or host terpenes at higher dosages. Instances of inhibition of nerve impulse activity from spontaneously active cells were observed during 3,2-MCHol and 3,2-MCHone stimulation, thus suggesting multifunctional effects for these compounds. The results help explain the role of chemicals in host selection, aggregation, and colonization behavior of the beetle and further elucidate hypotheses put forth in an earlier electroantennogram study.Texas Agricultural Experiment Station Paper NumberTA-18689. This research was supported in part by McIntire-Stennis Project 1525, the U.S. Department of Agriculture-sponsored program entitled The Expanded Southern Pine Beetle Research and Applications Program through TAES-SEA-CR grant 904-15-4, and NSF grant PCN 79-21708 to Oregon State University. The findings, opinions and recommendations expressed herein 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.     

Multiple acceptors for pheromonal enantiomers on single olfactory cells in the Douglas-fir beetle,Dendroctonus pseudotsugae Hopk. (Coleoptera: Scolytidae)

Olfactory perception of pheromonal enantiomers by male and female Douglas-fir beetles,Dendroctonus pseudotsugae Hopk. (Coleoptera: Scolytidae), was investigated by electrophysiological techniques and behavioral bioassays. Electroantennograms (EAGs) and single-cell responses indicated both sexes to be more responsive to racemic frontalin and the (–)-enantiomer at lower dosages. At higher dosages, little difference was noted in responses to either enantiomer. However, response to the racemic mixture at higher dosages was slightly greater than responses to either enantiomer alone. In laboratory behavioral bioassays, responses to low concentrations of (–)-frontalin and the racemic mixture exceeded response to the (+)-enantiomer alone. At a higher concentration, responses to the racemic mixture or either enantiomer alone did not differ. The results indicate that separate enantiomer-specific acceptors may exist on the same pheromone receptor cell.Texas Agricultural Experiment Station paper No. TA-19841. This research was supported in part by Mclntire-Stennis Project 1525, the U.S. Department of Agriculture-sponsored program entitled The Expanded Southern Pine Beetle Research and Applications Program through TAES-SEA-CR grant 904-15-4, and NSF grant PCN 79-21708 to Oregon State University. The findings, opinions and recommendations expressed herein 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.Mention of a trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.