Attractive and inhibitory pheromones produced in the bark beetle,Dendroctonus brevicomis,during host colonization: Regulation of inter- and intraspecific competition

Quantities of attractive (exo-brevicomin and frontalin) and inhibitory (trans-verbenol, verbenone, and ipsdienol) pheromones were monitored in both sexes ofDendroctonus brevicomis during their colonization of a ponderosa pine. Verbenone was found in males in the greatest amounts at the time of landing, and it declined more rapidly than the other pheromones in either sex. The amounts of frontalin andexo-brevicomin in males and females, respectively, increased after initial boring within the host but began to decline after mating. The quantity oftrans-verbenol in both sexes (females had significantly more) declined more gradually thanexo-brevicomin, frontalin, and verbenone. Ipsdienol was found only in males during the initial stages of attack when encountering the resin. It is suggested that along with a general decline in all pheromonal components, a sufficient change in the ratio of the attractive pheromones to an inhibitory pheromone,trans-verbenol, may play a role in termination of aggregation.trans-Verbenol may also function along with verbenone and ipsdienol in limiting the density of attack and thus intraspecific competition. These inhibitory pheromones also appear to cause several competing species of bark beetle to avoid landing in areas infested withD. brevicomis, even when their own pheromone is present.Coleoptera:Scolytidae. These studies were supported in part by the Rockefeller Foundation, USDA Forest Service, Regional research project W-110, SEA/ USDA, and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BMS 75-04223) to the University of California.     

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

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

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

Dendroctonus brevicomis was attracted to a mixture of theIps paraconfusus pheromones, ipsenol,cis-verbenol, and ipsdienol at 10^–9 g each/l but was not attracted to these pheromones at higher and lower release rates.I. paraconfusus was not attracted to theD. brevicomis pheromonesexo-brevicomin, frontalin, and myrcene at any release rate tested. Increased release rates of a mixture of the three pheromones ofI. paraconfusus inhibited the attraction ofD. brevicomis to its synthetic pheromones. A mixture of ipsenol + ipsdienol orcis-verbenol alone failed to cause inhibition indicating that at least two of theI. paraconfusus pheromones are required to inhibit the response ofD. brevicomis. The pheromones ofD. brevicomis did not inhibit the attraction ofI. paraconfusus to its pheromones; however, verbenone was a potent inhibitor.Coleoptera: Scolytidae. This paper is based in part upon a dissertation submitted by J.A.B. to the University of California, Berkeley, in partial fulfillment of the requirements for the Ph.D. degree in entomology, June 1978. These studies were supported by the Rockefeller Foundation; USDA Forest Service; Regional research project W-1 10, SEA/ USDA; and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BMS 75-04223) to the University of California. The findings, opinions, and recommendations are not necessarily those of the University of California or the funding agencies.     

Secondary attraction inGnathotrichus retusus and cross-attraction ofG. sulcatus (Coleoptera: Scolytidae)

Laboratory bioassays indicated that frass produced byGnathotrichus retusus males and male gut extracts were attractive to both sexes of beetles. The frass became attractive to females within 2 days of the commencement of boring activity, and attractive frass was produced for at least lOdays. Attraction of frass rose sharply after pairing of males with females. However, this increase in attraction could be due to increased boring activity and pheromone production by males following establishment of the mutualistic fungus. In field trapping experiments, male-infested logs were always highly attractive, but in one experiment, female-infested logs and logs infested by both sexes were also attractive. Thus, females could be involved in secondary attraction. High cross-attraction ofG. sulcatus toG. retusus infested logs in field experiments, as well as a moderate but significant response byG. retusus to sulcatol in the laboratory, suggests that they share sulcatol as a common pheromone.Research supported by Canadian Forestry Service Science Subvention Grant, National Research Council of Canada Operating Grant No. A3881, National Science Foundation (U.S.A.) Operating Grant No. PCM74-13643-A02, and the Council of Forest Industries of British Columbia.     

Semiochemicals produced by western balsam bark beetle,Dryocoetes confusus Swaine (Coleoptera: Scolytidae)

The most prominent beetle-produced volatiles identified in the abdominal extracts of maleDryocoetes confusus Swaine after they had bored for 24 hr in logs of subalpine fir,Abies lasiocarpa (Hook.) Nutt. were:exo andendo-brevicomin,trans-verbenol, verbenone, myrtenol,trans-pinocarveol,cis- andtrans-p-menthen-7-ol, 3-caren-10-ol, and several monoterpenes and sesquiterpenes. Myrtenol was the only conspicuous compound in extracts from males that had been exposed toA.lasiocarpa resin volatiles for 24 hr. Laboratory bioassays indicated that both (–)- and (+)-exo-brevicomin were attractive to femaleD. confusus, and that the (–) enantiomer did not inhibit response to its antipode. Results from field trapping experiments indicated that bothero-brevicomin and myrtenol are aggregation pheromones forD. confusus.exo-Brevicomin baits were effective in causing attack byD. confusus on baited and surrounding trees, suggesting that this pheromone may have utility in manipulating populations of the beetle.Research supported by the Natural Sciences and Engineering Research Council of Canada, Operating Grants A3881 and A3706 and Strategic Grant G1039.     

Primary Attraction of the Fir Engraver, Scolytus ventralis

In laboratory bioassays, Porapak Q-captured and steam-distilled volatiles from the bark of host trees, Abies grandis, particularly from root-rot-infected trees, attracted 50–70% of male and female fir engravers, Scolytus ventralis. Gas chromatographic–electroantennographic detection (GC-EAD) analyses of Porapak Q-captured bark volatiles revealed 19 EAD-active compounds of which 13 (mostly monoterpenes) were identified by GC–mass spectrometry (GC-MS). In separate field experiments, multiple-funnel traps baited with two blends of these 13 synthetic volatiles released at 280 and 340 mg/ 24 hr attracted 66 and 93% of the total S. ventralis captured, respectively. The clerid predator, Thanasimus undulatus, also responded strongly to the kairomonal volatiles. Additional experiments produced no evidence for aggregation pheromones in S. ventralis. These included laboratory bioassays and GC and GC-EAD analyses of Porapak Q-captured volatiles from male- and female-infested logs or trees undergoing mass attack in the field, GC analyses and/or bioassays of extracts from female accessory glands, extracted volatiles from emerged, attacking and juvenile hormone-treated beetles of both sexes, and videotape analysis of the behavior of attacking beetles on the bark surface. We argue against the hypothesis of pheromone-mediated secondary attraction in S. ventralis and conclude that the attack dynamics of this species can be explained solely by its sensitive primary attraction response to host volatiles.     

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.     

Feeding and boring behavior of the bark beetle,Ips paraconfusus,in extracts of ponderosa pine phloem

MaleIps paraconfusus Lanier bored and fed in cellulose powder substrates treated with solvent extracts of ponderosa pine phloem in preference to cellulose powder alone. Stimuli that elicit boring and feeding behavior occurred in the water extracts and the combined solvent extracts. No significant boring or feeding occurred in the methanol extract. There was a preference for, but no significant feeding in, the water partition of the ether extract. Feeding, but no preferential boring, occurred in the ether extracts.Coleoptera: Scolytidae.Research supported by the Rockefeller Foundation, an NIH Training Grant, USDA/SEA Regional Research Project W-110, and the USDA Forest Service.From a thesis submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy, by J.S.E., 1979, University of California, Berkeley, California.     

Some aspects of oviposition site selection inMonochamus notatus andM. scutellatus (Coleoptera: Cerambycidae)

The composition of monoterpene hydrocarbons and water content of freshly felled white pine logs (unattractive toMonochamus for oviposition) was compared to that of the same logs after aging long enough to become attractive toMonochamus. No significant differences were found. Variations between trees was the greatest source of variance in the data. If monoterpenes are used in host selection they are probably used to locate the host species and not to identify logs suitable for oviposition.     

Aggregation pheromone of the male granary weevil,Sitophilus granarius (L.)

Evidence for a male-produced aggregation pheromone inSitophilus granarius is reported. Hexane extracts of Tenax®-trapped volatiles from males held on wheat were attractive to both sexes in a multiple-choice olfactometer and pitfall bioassay chamber. A quantitative relationship existed between days of insect exposure on disks and degree of responsiveness. The maximum response was to 35 insect-day-equivalents. Diel-related activity showed both sexes responsive during photophase and nonresponsive during scotophase.Coleoptera: Curculionidae.Contribution to Regional Research Project NC151, Marketing and Delivery of Quality Cereals and Oilseeds in Domestic and Foreign Markets.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Behavior of the western pine beetle during host colonization

After living ponderosa pines were baited with either female-infested bolts or synthetic pheromones,Dendroctonus brevicomis were caught on sticky screens throughout trapping periods of 15–46 days; however, large numbers of beetles were trapped during only a small portion (5–10 days) of these trapping periods. The most attractive portions of trees attacked contained 3–6 beetles dm², in galleries ca. 2 cm long. Catch increased following addition of males to female-infested bolts, supporting the hypothesis that male-produced frontalin is an attractive pheromone of the western pine beetle. Catch at bolts removed from trees under attack was strongly dependent upon levels of boring activity. We found no evidence of interruption of the response to attractants during host colonization.Coleoptera: Scolytidae. Trade names and commercial enterprises or products are mentioned solely for information and do not constitute endorsement by the U.S. Department of Agriculture or University of California.     

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.     

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

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

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

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

Synthesis of sex pheromones of lesser peachtree borer and peachtree borer

The sex pheromones produced by females of the lesser peachtree borer,Synanthedon pictipes (Grote and Robinson), and the peachtree borer,Synanthedon exitiosa (Say), (E,Z)- and (Z,Z)-3,13-octadecadien-1-ol acetate, respectively, were synthesized from 1,8-dichlorooctane, lithium acetylide, and ethylene oxide. In the course of the synthesis a new carbon-oxygen cleavage reaction of homopropargylic acetals was found, and the stereochemistry of the dissolving metal reductions of acetylenic alcohols was investigated.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of that product by the USDA.     

Ethanol and ambrosia beetles in Douglas fir logs with and without branches

November-felled Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) logs with and without branches were left lying on the forest floor through August. In May, as the logs were being colonized by ambrosia beetles,Trypodendron lineatum (Oliv.) andGnathotrichus retusus (LeConte), the ethanol, acetaldehyde, and water concentrations in the delimbed logs were significantly higher than in the branched logs. Since both log types received the same rainfall, lower water contents in branched logs was probably the result of absorbed water being transported through the branches via capillary movement and evaporation. Lower tissue water levels could have prevented the establishment and maintenance of anaerobic conditions, thus limiting the synthesis of acetaldehyde and ethanol in the branched logs. By late August, the beetle densities in delimbed logs were 9–16 times greater than in the branched logs. Log ethanol concentrations could be a key chemical factor affecting the ambrosia beetle attack densities. Acetaldehyde concentrations in the logs also may have affected the attack densities.     

Aggregation pheromone ofCarpophilus dimidiatus (F.) (Coleoptera: Nitidulidae) and responses toCarpophilus pheromones in South Carolina

The major component of the male-produced aggregation pheromone ofCarpophilus dimidiatus (F.) is (3E, 5E, 7E, 9E)-6,8-diethyl-4-methyl-3,5,7,9-dodecatetraene. It attracts beetles of both sexes in the field and is synergized by odors from fermenting bread dough; mean trap catches for the tetraene alone, tetraene plus dough, dough alone, and control were 24.5, 48.3, 0.02, and 0.00, respectively. In the laboratory, individual males produced 0.58 µg±0.35 µg (SD) of the tetraene per day, but males in groups of 10–50 produced <2% as much per beetle. A second male-specific compound, (3E, 5E, 7E, 9E)-5,7-diethyl-9-methyl-3,5,7,9-tridecatetraene, was also identified fromC. dimidiatus and is about 5% as abundant as the major pheromone component.Carpophilus flight activity was monitored for one year in South Carolina corn fields with the pheromones forC. dimidiatus, C. freemani Dobson,C. mutilatus Erichson,C. hemipterus (L.),C. lugubris Murray, andC. obsoletus Erichson, all in combination with bread dough. The first four of these species accounted for 18, 70, 5.7, and 0.03%, respectively, of the totalCarpophilus trapped, but noC. lugubris orC. obsoletus were captured. Captures ofC. freemani were as high as 11,400/trap/week. Species specificity for the first four pheromones was high, except that a synthetic impurity in theC. dimidiatus pheromone was somewhat attractive toC. freemani andC. mutilatus. Three other species captured.C. antiques Melsheimer,C. marginellus Motschulsky, andC. humeralis (F.), accounted for 0.005, 5.0, and 1.3% of the total catch, respectively.C. antiquus was attracted primarily to the pheromone ofC. dimidiatus, butC. marginellus andC. humeralis responded to most of the test pheromones. There were two major periods ofCarpophilus flight activity: February through June and September through November.Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the names by USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Field response of spruce bark beetle,Ips typographus,to aggregation pheromone candidates

Six compounds previously identified from hindguts of unmated maleIps typographus (L.) during host colonization: 2-methyl-3-buten-2-ol (MB),cis-verbenol (cV),trans-verbenol (tV), myrtenol (Mt),trans-myrtanol (tM), and 2-phenylethanol (PE), were tested for their attractivity in the field with a subtractive method. The amounts of MB and cV released from a pipe trap were similar to those given off from the commercial bait Ipslure as well as that from a Norway spruce tree,Picea abies (L.) Karst., under mass attack. The blend of the compounds became nonattractive when either MB or cV was subtracted, while subtraction of any of the other four compounds had no effect. Addition of ipsdienol (Id) to the blend did not significantly increase the attraction. In a second comparative test, the addition of three compounds as a group (tV + Mt + PE) to MB + cV again had no effect on the attraction, but the addition of Id increased the catch somewhat. Addition of host logs to a bait releasing MB + cV at a rate lower than in previous experiments did not influence the attraction to pipe traps. Sticky traps containing natural pheromone sources (50 males in a log), which released 1–5 mg/day of MB as determined by aerations with deuterated MB as internal standard, were less attractive than a synthetic source releasing similar amounts of MB.Coleoptera: Scolytidae.This study was made within the Swedish project Odour Signals for Control of Pest Insects.     

Identification of the California red scale sex pheromone

Pheromone components of female California red scale,Aonidiella aurantii (Maskell) were isolated from airborne collections and found to be 3-methyl-6-isopropenyl-9-decen-1-yl acetate and (Z)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate. Both enantiomers of the latter compound as well as the corresponding enantiomers of theE isomer were prepared from (S)- or (R)-carvone. Bioassays with each of the four isomers showed that only theR,Z isomer attracted male red scale. Aonidiella aurantii (Maskell) (Homoptera: Diaspididae).This research was supported by a USDA Cooperative Research Grant.     

Aggregation pheromones of the flat grain beetle,Cryptolestes pusillus (Coleoptera: Cucujidae)

Aggregation pheromones were isolated fromCryptolestes pusillus (Schönherr), a coleopteran pest of stored products. Porapak Q-captured beetle and frass volatiles were fractionated by preparative gas-liquid chromatography. The fractions were bioassayed with an arena olfactometer and/or with a two-choice, pitfall olfactometer. Three biologically active, male-produced compounds eliciting aggregation behavior from adultC. pusillus were isolated and identified by spectroscopic methods as (Z)-3-dodecenolide (I), (Z)-5-tetradecen-13-olide (II), and (Z,Z)-3,6-dodecadienolide (III). Compound I was the major volatile produced and was active alone. Compound II was not active alone, but synergized the response to I. Compound III was active alone at higher concentrations, but did not significantly increase the response when added to the most active mixture of I and II, and so it is probably not part of the aggregation pheromone. Pheromone production increased dramatically when the insects were aerated on a food source.Research supported in part by the Natural Sciences and Engineering Research Council of Canada, Operating Grants A3881 and A3785, Strategic Grant 60958, and a Graduate Scholarship to J. G. Millar.