Attractant Semiochemicals of the

Engraver Beetle, Ips perturbatus, in

South-Central and Interior Alaska

Edward H. Holsten, Roger E. Burnside, and Steven J. Seybold

United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

Research Paper

PNW-RP-529

December 2000
This publication reports research involving pesticides. It does not contain

recommendations for their use, nor does it imply that the uses discussed here

have been registered. All uses of pesticides must be registered by appropriate

state and federal agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable

plants, and fish or other wildlife—if they are not handled or applied properly.

Use all pesticides selectively and carefully. Follow recommended practices for

the disposal of surplus pesticides and pesticide containers.

Authors Edward H. Holsten is a research entomologist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 3301 C Street,

Suite 200, Anchorage, AK 99503-3954; Roger E. Burnside is an entomologist, State of Alaska, Department of Natural Resources, Division of Forestry,

550 W. 7th Ave., Suite 1450, Anchorage, AK 99501; and Steven J. Seybold

is an assistant professor, Departments of Entomology and Forest Resources,

University of Minnesota, St. Paul, MN 55108.
Abstract Holsten, Edward H.; Burnside, Roger E.; Seybold, Steven J. 2000. Attractant

semiochemicals of the engraver beetle, Ips perturbatus, in south-central and

interior Alaska. Res. Pap. PNW-RP-529. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Research Station. 9 p.

From 1996 through 1999, field tests of various engraver beetle (Ips perturbatus

(Eichhoff)) semiochemicals in funnel traps were conducted in south-central and

interior Alaska in stands of Lutz (Picea ×lutzii Little) and white spruce (P. glauca

(Moench) Voss). The European spruce beetle (I. typographus (L.)) is believed to be

taxonomically similar to I. perturbatus. Commercially available European spruce

beetle lures, which include 2-methyl-3-buten-2-ol, however, were no more attractive

to I. perturbatus than the combination of racemic ipsdienol and 83%-(+)-cis-verbenol.

The addition of >97%-(—)-ipsenol to ipsdienol and cis-verbenol, however, was more

attractive than the binary combination alone. Racemic ipsenol dispersed from bubble

caps did not prevent I. perturbatus from colonizing fresh logging debris. Thus ipsenol

was found to function as an attractant rather than as an antiaggregant as previously

shown.

Keywords: Bark beetles, Ips perturbatus, semiochemicals, pheromones, aggregation

pheromones, antiaggregation pheromones, white spruce, Picea glauca, Lutz spruce,

Picea ×lutzii, Alaska (interior, south-central).

Data from 3 years of field and laboratory studies on the efficacy of potential engraver

beetle (Ips perturbatus (Eichhoff)) semiochemicals are summarized. The addition of

cis-verbenol to racemic ipsdienol caught significantly higher numbers of beetles than

ipsdienol alone. The addition of 2-methyl-3-buten-2-ol did not affect trap catches.

Ipsenol [racemic or >97%-(—)] did not reduce trap catches as anticipated. Rather,

when combined with ipsdienol and cis-verbenol, ipsenol more than doubled trap

catches. Future research will concentrate on the role of verbenone as an antiaggregant

of I. perturbatus to interrupt its response to ipsdienol, cis-verbenol, and ipsenol or to

naturally derived aggregation pheromone.

Summary
Contents 1 Introduction

2 Materials and Methods

2 Laboratory Studies of Production and Response to Semiochemicals by

Ips perturbatus

2 Field Studies of Response to Semiochemicals by Ips perturbatus

3 Placement

4 Experimental Design

4 Results and Discussion

4 Laboratory Studies of Production and Response to Semiochemicals by

Ips perturbatus

4 Field Studies of Response to Semiochemicals by Ips perturbatus

7 Conclusions

7 Acknowledgments

7 English Equivalents

8 Literature Cited
1

Introduction The engraver beetle (Ips perturbatus (Eichhoff)) (Coleoptera: Scolytidae), is distributed

transcontinentally in the boreal region of North America, generally after the distribution

of white spruce (Picea glauca (Moench)) Voss (Bright 1976, Wood 1982). It colonizes

standing white spruce and Lutz spruce (P. ×lutzii Little) stressed by natural disturbances

such as drought; flooding; wind, ice, and snow damage; and human disruptions such as

logging activity and rights-of-way clearance (Holsten and Werner 1987). It also readily

colonizes fallen trees and tree debris from these disruptions. Normally, endemic populations may infest individual standing spruce trees, but during warm, dry summers after

mild winters, engraver beetle populations can increase significantly and kill groups of

standing spruce trees.

After a 1983 wildfire and excessive ice and snow damage in the Fairbanks, Alaska,

area, high engraver beetle populations in 1986 and 1987 killed trees on more than

6475 ha (Holsten 1986). In Alaska, most damage by I. perturbatus has occurred in

interior white spruce forests. Historically, only limited tree mortality has been caused by

this beetle in Lutz spruce forests in south-central Alaska. In 1996, however, more than

47 percent of the residual spruce in a thinned area near Granite Creek in south-central

Alaska became infested with I. perturbatus and I. tridens (Mannerheim). Spring drought

conditions apparently led to this rapid increase in Ips activity in 1996 (Holsten 1996,

1997, 1998). Increases in tree mortality in Alaska caused by Ips species has stimulated

research efforts in developing new management strategies using semiochemical

approaches.

Aggregation pheromone production has been described and reviewed for over

30 bark beetle species (Borden 1982, 1985). Research on pheromone isolation and

identification has prompted much interest during the last decade in the application of

pheromones and other semiochemicals to manipulate bark beetle populations (Salom

and Hobson 1995, Shea 1994).

From 1977 through 1992, field tests of the efficacy of various bark beetle semiochemicals showed that ipsdienol (ID = 2-methyl-6-methylene-2,7-octadien-4-ol) and

2-methyl-3-buten-2-ol (MB) were generally attractive to I. perturbatus, whereas ipsenol

(IE = 2-methyl-6-methylene-7-octen-4-ol), 3-methylcyclohex-2-enone (MCH), and

verbenone were generally inhibitory (Werner 1993). Racemic ID alone caught 84

percent more beetles than racemic IE alone and 62 percent more beetles than the

combination of racemic ID and racemic IE. The addition of racemic IE to MB reduced

beetle trap catches by 38 and 92 percent, respectively. Also, the addition of MCH and

verbenone to ID-baited traps reduced trap catches by 31 and 19 percent, respectively.

No beetles were caught in traps baited with either cis- or trans-verbenol, but these two

compounds were never tested in combination with ID.

Surprisingly, Werner (1993) also showed racemic exo-brevicomin (a Dryocoetes spp.

and Dendroctonus spp. attractant) was slightly attractive alone to I. perturbatus and

when combined with racemic ID, elicited the highest field response in one experiment.

Field studies utilizing bubble cap (bc) formulations of racemic IE to reduce the number

of attacks on standing trees yielded mixed results. Werner (1993) also reported that

newly emerged adult I. perturbatus moving to hibernation sites were not responsive to

racemic ID.

Building on research results of Werner (1988, 1993) and stimulated in 1996 by

increased Ips activity in south-central Alaska, efforts to apply Ips attractants and

antiaggregants for population manipulation were renewed in south-central and interior

Alaska.
2

Materials and

Methods

From 1996 through 1998, the following objectives were developed and tested through

laboratory and field studies:

1. Determine which attractant and antiaggregant pheromones are produced by

I. perturbatus through chemical (gas chromatography [GC] and mass spectrometry

[MS]), and neuronal analyses (electroantennogram detection [EAD])

2. Determine the efficacy of various compounds and their enantiomers of

I. perturbatus attractants and antiaggregants through field studies with baited funnel

traps

3. Determine the efficacy of candidate antiaggregants as deterrents to colonization by

I. perturbatus of white and Lutz spruce logging slash in south-central Alaska

Immature and mature I. perturbatus were collected in infested Lutz spruce logging

debris from the Granite Creek campground area, 150 km south of Anchorage, Alaska,

in June 1998 and shipped to the University of Nevada, Reno for rearing (Browne 1972)

and analyses of semiochemicals. To date, no method has been developed to distinguish

the sexes of this species without dissecting genitalia. Sex can be determined when

insects are dissected while making semiochemical extracts, but sex cannot be

determined in living insects. Porapak or solid phase microextrac-tion (SPME) collections

cannot therefore be made on pure-sex groups of beetles.

Gas chromatography and MS analyses were conducted on Porapak extracts of volatiles

produced by newly emerged adults feeding in green logs of Lutz spruce and on abdominal extracts of males and females that had been previously fed on Lutz spruce phloem

or treated topically with juvenile hormone III (JH III). Specific methods for preparing

extracts and for chemical analysis will be published separately, but techniques generally

followed those described in Seybold and others (1995a, 1995b) and Tillman and others

(1998).

In addition to these analyses, Porapak extract of both sexes of I. perturbatus feeding

in green logs of Lutz spruce was analyzed by using GC-MS.1 This extract also was

used as the stimulus in a lab study using coupled GC-EAD2 with unknown sexes of

I. perturbatus at Simon Fraser University.

Field studies in Alaska were conducted on three individual stands having different

characteristics:

Mature white spruce stands, 300 m in elevation in the Bonanza Creek Experimental

Forest, 40 km west of Fairbanks, were 165 years old with an average diameter of

32 cm, an average height of 30 m, and a stand density of 875 trees per ha.

Young white spruce stands 500 m in elevation near Tok, Alaska, originated from a fire

about 80 years ago. Recently, these stands have been thinned to about 1,400 stems per

ha with an average diameter of 9.5 cm and an average height of 10 m, including 20

stems per ha of quaking aspen (Populus tremuloides Michx.) in the residual stands.

Laboratory Studies

of Production and

Response to

Semiochemicals by

Ips perturbatus

Field Studies of

Response to

Semiochemicals by

Ips perturbatus

1 Professor Wittko Franke. 1999. Institute of Organic

Chemistry, University of Hamburg, Edmund-Siemers-Allee

ID-20146. Hamburg, Germany.

2 Regine Gries. 1999. Simon Fraser University, 8888

University Drive, Burnaby, BC V5A 156.
3

Table 1—Release rates of synthetic semiochemicals used in Ips perturbatus

trapping studies, Alaska, 1997-99a

Treatment Stereochemistry Bubble cap amount Release rate

 Mg Mg per day

Ipsdienol Racemic 40 0.2

Ipsenol Racemic 20 .2

Ipsenol 97%-(—) 20 .2

cis-verbenol 83%-(+) 75 .6

Ips LureR and EcolureR:

 2-methyl-3-buten-ol 1400 40.0

 and (-)-cis-verbenol (—) 70 2.0

 and ipsdienol Racemi 15 .6

a All semiochemicals have chemical purity greater than 98 percent.

Shrub cover in both the Fairbanks and Tok sites was sparse with only green alder

(Alnus crispa (Ait.) Pursh), crowberry (Empetrum nigrum L.), Labrador-tea (Ledum

groenlandicum L.), mountain-cranberry (Vaccinium vitis-idaea L.), and high bushcranberry (Viburnam edule (Michx.) Raf.) occupying the sites.

Young, residual Lutz spruce stands 250 m in elevation in the Granite Creek campground

area, 150 km south of Anchorage, Alaska, were about 90 years old with an average

diameter of 7.5 cm, an average height of 10 m, and a stand density of about 600 trees

per ha. Shrub cover in the Granite Creek area was sparse, being occupied mostly by

blue-joint reedgrass (Calamagrostis canadensis (Michx.) Beauv.) and Salix spp.

Semiochemicals (table 1) were dispersed from slow-release polyethylene bc

(PheroTech, Inc, Delta, BC, Canada3) placed in 12-unit Lindgrenmultiple funnel traps

(Lindgren 1983). Funnel traps were either hung from branches of nonhost trees or dead

spruce or suspended from a nylon rope tied between two trees in such a way that the

collection container of the trap was 0.3 m aboveground. All traps were placed at least

30 m apart. Beetles were collected from the traps weekly from late May through the end

of July. Trapped insects were placed in labeled plastic bags and frozen for later identification and counting.

Trap Placement

3 The use of trade or firm names in this publication is for

reader information and does not imply endorsement by the

U.S. Department of Agriculture of any product or service.
4

Table 2—Effect of cis-verbenol on the response of Ips perturbatus to racemic

ipsdienol released from Lindgren funnel traps, Fairbanks and Granite Creek,

Alaska, 1997

Number of beetles caught (mean + SE)

Treatment Fairbanks Granite Creek

Racemic ipsdienol 8.1 + 2.3 44.5 + 30.9

Racemic ipsdienol and cis-verbenol 54.7 + 19.4 448.0 + 165.6

Unbaited control 3.6 + 2.4 14.2 + 9.6

Treatments for all field tests were replicated at least five times in either randomized

complete block designs or line transects. Treatments consisted of various

semiochemicals with unbaited traps as controls.

Gas chromatography and GC-MS analyses of a Porapak extract from living insects of

both sexes feeding in green Lutz spruce logs for 1 week revealed IE [>99%-(—)], ID

[~90%-(+)], cis-verbenol, trans-verbenol, and verbenone in the volatile headspace.

This analysis was confirmed in part at the University of Hamburg (see footnote 1).

Also, using the same Porapak extract in collaborative studies as those used at Simon

Fraser University (see footnote 2), IE, ID, and an unknown compound each elicited

neuronal responses from the antenna of an unsexed live I. perturbatus in a GC-EAD

assay. Finally, extracts taken from dissected abdominal tissue of beetles of known

sex showed that JH treatment induced IE, ID, and cis-verbenol synthesis in male

I. perturbatus.4

In 1996, I. perturbatus populations increased to damaging levels in south-central

Alaska (Holsten 1996, 1997, 1998). The Ips species was believed to be I. tridens

(Mannerheim). Funnel trap studies were initiated in 1997 near Fairbanks (interior

Alaska) and in the Granite Creek area (south-central Alaska). Traps were baited with

racemic ID + cis-verbenol, an attractant pheromone previously identified for I. tridens

in Canada (Moeck and others 1985). In south-central Alaska, addition of cis-verbenol

caught at least 10 times more beetles than ID alone (table 2). Later during the 1997

field season, the most abundant Ips species in south-central Alaska was determined to

be I. perturbatus not I. tridens. It seems that adding cis-verbenol greatly enhances the

response of I. perturbatus to ID.

Experimental Design

Results and

Discussion

Laboratory Studies

of Production and

Response to

Semiochemicals by

Ips perturbatus

Field Studies of

Response to

Semiochemicals by

Ips perturbatus

4 Seybold, S.J. Identification of Ips perturbatus attractant

pheromones through gas chromatography and mass

spectrometry. Manuscript in preparation. On file with:

S.J. Seybold, Departments of Entomology and Forest

Resources, University of Minnesota, St. Paul, MN 55108.
5

Table 3—Effect of 2-methyl-3-buten-2-ol on the response of Ips perturbatus

to racemic ipsdienol and cis-verbenol released from Lindgren funnel traps,

Granite Creek, Alaska, 1998

No. of beetles caught

Treatment (mean + SE)

Ipsdienol and cis-verbenol 87.1 + 15.8

Ipsdienol and cis-verbenol

 and 2-methyl-3-buten-2-ol (Ips Lure) 94.3 + 29.5

Ipsdienol and cis-verbenol

 and 2-methyl-3-buten-2-ol (Ecolure) 67.0 + 16.8

Unbaited control 19.1 + 10.9

Ips perturbatus is believed by some to be taxonomically similar to I. typographus, a

serious killer of conifers in Europe (Wood 1982). Bakke (1982) identified the attractant

pheromone complex of I. typographus. The blend is composed of ID + cis-verbenol+ 2-

methyl-3-buten-2-ol (MB). We tested two commercially available I. typographus pheromone baits (Ips LureR and EcolureR, both with high dosages of MB) and compared them

to our two-component attractant (ID + cis-verbenol). We found no difference in response of I. perturbatus to the commercial I. typographus baits or to the two-component

bait we developed (table 3). Earlier, Werner (1993) showed an antiattractant effect when

MB was added to ID. Werner, however, did not test ID + cis-verbenol, which may

explain the mixed results that occurred in his earlier studies and why we were not able to

inhibit the response of I. perturbatus to cis-verbenol and ID with MB.

In 1999, we undertook two Ips pheromone field studies—one in Tok (interior Alaska)

and the other at the Granite Creek area. The objective of the Granite Creek study was to

treat fresh logging slash with bc filled with racemic IE to keep engraver beetle populations from breeding in this highly susceptible host material. Untreated slash served as a

control. The choice of racemic IE was based on results reported by Werner (1993).

The experiment had three treatments, replicated five times, and plot size was 10 m2 :

(1) 9 racemic IE bc/plot, (2) 25 racemic IE bc/plot, and (3) an untreated check. Bubble

caps were stapled on the south side of a 1-m stake and uniformly spaced throughout

the plot. Contrary to our expectations, the plots treated with IE apparently had higher

I. perturbatus attack rates, as determined by linear 0.3-m samples, than the untreated

slash (table 4).
6

Table 4—Effect of racemic ipsenol on the response of Ips perturbatus

to fresh logging debris, Granite Creek, Alaska, 1999

Number of attacks per linear 0.3 m

Treatment (mean + SE)

9 bubble capsa 8.2 + 1.3

25 bubble capsa 10.7 + 4.9

Unbaited control 5.8 + 0.7

a Racemic ipsenol.

Table 5—Effect of 97%-(—)-ipsenol on the response of Ips perturbatus

to racemic ipsdienol and cis-verbenol in baited funnel traps, Granite

Creek and Tok, Alaska, 1999a

 No. of beetles caught

 (mean + SE)

Treatment Granite Creek Tok

Racemic ipsdienol and cis-verbenol 191.1 + 51.2 330 + 13.3

Racemic ipsdienol and cis-verbenol

 and >97%-(—)-ipsenol 962.3 + 190.7 555 + 33.1

>97%-(—)-ipsenol 110 + 30.0

Unbaited trap 4.0 + 0.6 5.5 + 1.1

a Tok trapping study had 1 additional treatment: >97%-(—)-ipsenol alone.

Based on these findings, it seemed racemic IE acted as an attractant to I. perturbatus.

Having determined I. perturbatus produces >99%-(—)-IE, we obtained >97%-(—) IE

bcs from PheroTech and completed a replicated funnel trap study in the Granite Creek

area comparing control (empty traps), ID and cis-verbenol, and >97%-(—)-IE and ID

and cis-verbenol. Each treatment was replicated seven times. Based on the work of

Werner (1993), we expected to see a significant reduction in trap catches with the

addition of >97%–(—)-IE. Results (table 5) of this study, however, indicated that the

addition of >97%-(—)-IE significantly enhanced the response to the two-component

attractant (ID and cis-verbenol).

The 1999 studies near Tok involved replicated funnel traps comparing the following

treatments: (1) cis-verbenol + racemic ID; (2) cis-verbenol + racemic ID +

>97%-(—)-IE; (3) >97%-(—)-IE alone; and (4) control (empty traps). Results

demonstrated that adding >97%-(—) IE increased, from two to seven times, the number

of engraver beetles trapped compared to the two-component attractant (table 5).
7

We now have a strong attractant for I. perturbatus (ID + cis-verbenol + IE). Because

IE is produced by male beetles after JH treatment, appears in the headspace above

feeding males and females, elicits an antennal response in EAD assays, and enhances

response to ID and cis-verbenol in field studies, it should be regarded as an attractive

pheromone for I. perturbatus and an important component in its synthetic attractant

blend. This result is in contrast to the earlier results found by Werner (1993); perhaps

because of variation in population or to differences in trapping technique. Ipsdienol

also seems to be an attractive pheromone for I. perturbatus given its production and

antennal activity combined with field tests. The cis-verbenol is produced by I. perturbatus and enhances field response, but we had no evidence for its activity in the

EAD assays; perhaps because it was present in low quantities in the Porapak extract.

Additional EAD assays with cis- and trans-verbenol as well as verbenone may be

needed.

Future laboratory and field studies will concentrate on the role of verbenone in the

semiochemical complex of I. perturbatus. Verbenone is produced and released when

both sexes feed in Lutz spruce logs for 1 week, and perhaps is released late in the

colonization process as an interruptant. As previously noted, Werner (1993) showed

a 19-percent reduction in trap catch when verbenone was added to ID. Laboratory

bioassays with Ips paraconfusus (McPheron and others 1997) showed that increasing concentrations of verbenone resulted in slower responses by beetles reaching an

attractant source of naturally produced male pheromone volatiles. Similar laboratory

assays could be conducted with verbenone as an interruptant for a Porapak extract of

male and female I. perturbatus volatiles.

We thank John Hard, recently retired from the USDA Forest Service PNW Research

Station, Kathy Matthews and Ken Zogas of Forest Health Management, State and

Private Forestry, Alaska Region, Anchorage, Alaska, for help with the installation of the

field studies and trap collections. We also thank personnel from the Tanana Chiefs

Council, Fairbanks, Alaska, for assistance in the field studies conducted in Tok.

Research by Steven J. Seybold was supported by USDA Forest Service Pacific

Southwest Research Station Cooperative Agreement PSW-0028-CA.

When you know: Multiply by: To find:

Celsius (0

C) 1.8 and add 32 Fahrenheit

Centimeters (cm) 2.54 Inches

Hectares (ha) 2.47 Acres

Kilometers (km) 0.621 Miles

Meters (m) 3.281 Feet

Millimeters (mm) 0.254 Inches

Conclusions

Acknowledgments

English Equivalents
8

Bakke, A. 1982. The utilization of aggregation pheromone for the control of the spruce

bark beetle. In: Leonhardt, B.A.; Beroza, M., eds. Insect pheromone technology:

chemistry and applications. American Chemical Society Symposium. 190: 219-229.

Chapter 12.

Borden, J.H. 1982. Aggregation pheromones. In: Mitton, J.B.; Sturgeon, K.B., eds.

Bark beetles in North America conifers. Austin, TX: University of Texas Press:

74-139.

Borden, J.H. 1985. Aggregation pheromones. In: Kerkut, G.A.; Gilbert, L.I., eds.

Comprehensive insect physiology, biochemistry, and pharmacology. Oxford:

Pergamon Press: 257-289. Vol. 9.

Bright, D.E. 1976. The insects and arachnids of Canada. Part 2: The bark beetles of

Canada and Alaska, Coleoptera: Scolytidae. Publ. 1576. Canada Department of

Agriculture, Research Branch, Biosystematics Research Institute. 241 p.

Browne, L.E. 1972. An emergence cage and refrigerated collector for wood-boring

insects and their associates. Journal of Economic Entomology. 65: 1499-1501.

Holsten, E.H. 1986. Preliminary evaluation of an Ips perturbatus outbreak in the

Bonanza Creek Experimental Forest, Fairbanks, Alaska. Biological Evaluation R10-

86-1. Anchorage, AK: U.S. Department of Agriculture, Forest Service, Alaska

Region. 8 p.

Holsten, E.H. 1996. Ips tridens: a pest of managed stands? FHP Biological Evaluation

R10-TP-64. Anchorage, AK: U.S. Department of Agriculture, Forest Service, Alaska

Region. 7 p.

Holsten, E.H. 1997. Ips tridens: a pest of managed stands? 1997 update. FHP

Biological Evaluation R10-TP-71. Anchorage, AK: U.S. Department of Agriculture,

Forest Service, Alaska Region. 7 p.

Holsten, E.H. 1998. Ips perturbatus: A pest of managed stands? 1998 update. FHP

Biological Evaluation R10-TP-77. Anchorage, AK: U.S. Department of Agriculture,

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Holsten, E.H.; Werner, R.A. 1987. Engraver beetles in Alaska forests [Leaflet].

[Portland, OR]: U.S. Department of Agriculture, Forest Service, Pacific Northwest

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Lindgren, B.S. 1983. A multiple funnel trap for scolytid beetles (Coleoptera). Canadian

Entomologist. 115: 299-302.

McPheron, L.J.; Seybold, S.J.; Storer, A.J. [and others] 1997. Effects of enantiomeric blend of verbenone on response of Ips paraconfusus to naturally produced

aggregation pheromone in the laboratory. Journal of Chemical Ecology.

23: 2825-2839.

Moeck, H.A.; Safranyik, L.; Simmons, C.S.; Lawko, C.M. 1985. Ips tridens

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U.S. Department of Agriculture

Pacific Northwest Research Station

333 S.W. First Avenue

P.O. Box 3890

Portland, OR 97208

Official Business

Penalty for Private Use, $300

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