United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

Research Paper

PNW-RP-541

April 2002

Use of Semiochemicals of Secondary

Bark Beetles to Disrupt Spruce Beetle

Attraction and Survival in Alaska

Richard A. Werner and Edward H. Holsten
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 or

both, 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.

Richard A. Werner was a research entomologist (retired), Pacific Northwest Research

Station, 8080 NW Ridgewood Drive, Corvallis, OR 97330. Werner is currently a volunteer at the Pacific Northwest Research Station conducting research for the Long Term

Ecological Research Program in Alaska; and Edward H. Holsten is a research entomologist, Pacific Northwest Research Station, 3301 C Street, Suite 200, Anchorage,

AK 99503-3954.

Authors
Werner, Richard A.; Holsten, Edward H. 2002. Use of semiochemicals of secondary

bark beetles to disrupt spruce beetle attraction and survival in Alaska. Res. Pap.

PNW-RP-541. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Research Station. 11 p.

Field experiments using baited multiple-funnel traps and baited felled trees were conducted to test the hypothesis that semiochemicals from secondary species of scolytids

could be used to disrupt spruce beetle (Dendroctonus rufipennis (Kirby)) attraction.

Semiochemicals from three secondary species of scolytids, (Ips perturbatus (Eichhoff))

[(±)-ipsdienol], Dryocoetes affaber (Mannerheim) [(±)-exo- and (±)-endo-brevicomin],

and Polygraphus rufipennis (Kirby) [methyl butenol] were used to disrupt spruce beetle

trap catches and reduce attacks on felled trees. Trap catches of spruce beetles were

reduced by 87 percent by the combinations of semiochemicals from these secondary

scolytids. Addition of MCH (methylcyclohexenone) to these semiochemicals reduced attack density by 62 to 87 percent. Results indicate that inducing attacks by

I. perturbatus and D. affaber on felled susceptible host trees by using semiochemicals

could be a viable method to minimize spruce beetle attack and brood development.

Keywords: Dendroctonus rufipennis, Ips perturbatus, Dryocoetes affaber, Polygraphus

rufipennis, bark beetle, semiochemicals, Lutz spruce (Picea x lutzii), Alaska.

Field experiments were conducted from 1991 to 1993 on the Chugach National Forest

in south-central Alaska. Semiochemicals from secondary species of bark beetles such

as Ips perturbatus (Eichhoff) [(±)-ipsdienol], Dryocoetes affaber (Mannerheim) [(±)-exoand (±)-endo-brevicomin], and Polygraphus rufipennis (Kirby) [methyl butenol] were

added to traps baited with spruce beetle binary lure (frontalin plus α-pinene) to disrupt

attraction of the spruce beetle. These same semiochemicals were placed on felled Lutz

spruce at intervals along the tree bole to reduce attack density, gallery construction,

and brood production. The addition of (±)-exo- and (±)-endo-brevicomin plus methyl

butenol, and (±)-exo- and (±)-endo-brevicomin plus (±)-ipsdienol disrupted trap catch of

spruce beetles. The addition of either (±)-exo- and (±)-endo-brevicomin plus 3-methyl2-cyclohexen-1-one (MCH), or (±)-ipsdienol plus MCH to trees baited with spruce

beetle lures (frontalin plus α-pinene) reduced attack density by 87 percent and 62 percent, respectively, in stands with high populations of spruce beetles. The addition of

MCH to trees baited with frontalin plus α-pinene and (±)-ipsdienol reduced gallery construction by 40 percent and brood production by 50 percent in high populations. In low

and medium populations of spruce beetles, the addition of (±)-exo- and (±)-endobrevicomin plus (±)-ipsdienol and MCH to spruce beetle-baited trees disrupted gallery

construction by 63 percent (low) and 77 percent (medium) and brood production by 83

percent (low) and 81 percent (medium).

Abstract

Summary
1 Introduction

2 Materials and Methods

3 Chemical Descriptions

3 Trapping Experiments

3 Statistical Analysis for Trapping Experiments

3 Felled Tree Experiments

4 Statistical Analysis for Felled Tree Experiments

4 Results and Discussion

7 Conclusions

7 Acknowledgments

8 English Equivalents

8 Literature Cited

Contents
1

The spruce beetle (Dendroctonus rufipennis (Kirby)) infests most species of Picea in

North America (Schmid and Fyre 1977). White spruce (Picea glauca (Moench) Voss),

Sitka spruce (P. sitchensis (Bong.) Carr.), and the hybrid Lutz spruce (P. X lutzii Little)

are the major hosts in Alaska (Werner and others 1977). Most spruce beetle infestations in Alaska occur in white and Lutz spruce stands. Infestations have expanded

throughout south-central Alaska since 1974 and in the last 10 years have killed trees

on 1 416 450 ha of forest. Low populations of spruce beetles usually breed in windthrown trees where they can increase rapidly to epidemic levels (Holsten and others

1991). Wind-thrown trees are the most productive breeding sites for spruce beetles;

they may absorb and produce up to 10 times the number of beetles a standing tree will

absorb or produce (Dyer and Taylor 1971, Hodgkinson 1985). When spruce beetle

populations in wind-thrown trees increase to high levels, emerging beetles may then

enter susceptible, large-diameter, green standing timber. Almost all spruce beetle infestations in standing timber originate from wind-thrown trees or shaded right-of-way clearing debris (Holsten and others 1991). The death of individual trees and entire stands

represents large annual losses in forest resources including wildlife habitat (Holsten

and others 1995, Werner and Holsten 1983). Beetle-killed timber also increases fuel

loads within stands, which increases the risk of a catastrophic wildfire (Schulz 1995).

Research on the use of semiochemicals to manipulate bark beetle populations has

increased in the Pacific Northwest during the past 20 years (Borden 1982, 1985,

1989). This includes the use of both synthetic aggregation and antiaggregation

semiochemicals to prevent or reduce attack density of spruce beetles (Holsten 1994,

Werner 1994, Werner and Holsten 1995). This strategy has several advantages: (1)

use of traditional insecticides is minimal, (2) resistance of bark beetles to some groups

(antiaggregants) of semiochemicals might be impossible because successful brood development would be prevented, and (3) unlike insecticide treatment, little direct mortality to parasites and predators would occur.

Three beetle-produced compounds, 1-methyl-2-cyclohexen-1-ol (MCOL) (Dixon and

others 1992); 1,5-dimethyl-6,8-dioxabicyclo [3.2.1] octane (frontalin) (Gries and others

1988, Kinzer and others 1971, Libbey and others 1985); and 3-methyl-2-cyclohexen1-one (MCH) (Rudinsky and others 1974) play a significant role in the communication

system of the spruce beetle. The aggregation pheromone frontalin and MCOL, along

with the host tree monoterpene α-pinene, mediate host selection and aggregation

(Werner 1994; Werner and Holsten 1995; Wieser and others 1989, 1991). MCH inhibits

spruce beetle attacks and reduces brood production and development when attacks

are successful (Holsten and Werner 1984, 1985, 1986, 1987; Holsten 1994; Holsten

and others 1992; Werner 1994; Werner and Holsten 1995).

Intraspecific competition in attack and emergence density of bark beetles is nonlinear

and characteristic of populations where survival is density dependent (Berryman 1974).

Safranyik and Linton (1985) report the effects of intraspecific competition on the reproductive biology of spruce beetle. Their results indicate the presence of density-dependent compensatory processes within spruce beetle populations. Thomson and Sahota

(1981) showed that competition exists between parent adults during egg gallery construction and that it reduces gallery length and construction. These characteristics of

intraspecific competition are also present in interspecific competition when more than

one species coinhabits the same host (Birch 1957; Borden 1996; Brian 1956; Byers

and Wood 1980; Paine and Hanlon 1991; Poland 1997; Poland and Borden 1994,

1998a, 1998b; Rankin and Borden 1991).

Introduction
2

The frequency of co-occurrence of scolytid species within a discrete area of the phloem

is a useful indicator of their potential for competition (Paine and Hanlon 1991). Host attraction for secondary scolytids that compete with spruce beetles for space and food

resources may reduce spruce beetle development and survival. Brian (1956) describes

two forms of competition. Interference competition occurs when one species damages

the feeding resource of another species. Exploitation competition, the ability to detect,

occupy, and retain vacant resources necessary for survival is described by Rankin

and Borden (1991) for the pine engraver [Ips pini (Say)] and mountain pine beetle

(Dendroctonus ponderosae Hopkins). Rankin and Borden (1991) found that I. pini coexists with D. ponderosae in lodgepole pine (Pinus contorta var. latifolia Engelmann)

but that coexistence causes a reduction in numbers of progeny. Other instances of interspecific, semiochemical-based competition have been documented (Birch and Light

1977, Birch and Wood 1975, Birch and others 1980, Borden 1982, Borden and others

1992, Byers 1989, Byers and Wood 1980, Furniss and Livingston 1979, Light and others 1983, Rankin and Borden 1991).

The most important arthropod factor impacting spruce beetle populations is interspecific competition with other scolytid species (Gara and others 1995). Small scolytid species competed with spruce beetles in 73 percent of collected bark samples (100 cm2

) in

which spruce beetles were found.

The engraver beetle (I. perturbatus (Eichhoff)), a common scolytid that inhabits

spruce stands in Alaska, is attracted by racemic ipsdienol (Werner 1993). Other competitor scolytids found feeding in spruce are Dryocoetes affaber (Mannerheim) and

Polygraphus rufipennis (Kirby) (Gara and others 1995, Werner and Holsten 1984,

1995). These three scolytids commonly attack felled trees or standing trees that were

attacked initially by spruce beetles.

Field studies conducted from 1980 to 1991 in south-central and interior Alaska identified several scolytid pheromones and host terpenes such as seudenol, frontalin, and

α-pinene as aggregants for the spruce beetle (Werner and Holsten 1995). Frontalin

dispersed from sticky traps also caught Dryocoetes affaber and P. rufipennis. Field

trapping experiments in interior Alaska indicated that (±)-ipsdienol caught more

I. perturbatus in sticky traps and trap trees than (±)-ipsenol and a combination of

both (Werner 1993).

This information led to the hypothesis that attracting species of secondary bark beetles

to suitable spruce beetle hosts may interfere with spruce beetle development and survival, thereby reducing the probability of spruce beetle population buildup, which could

develop into a major infestation. We also hypothesize that, in addition to formulated

MCH treatments, an increase in secondary scolytid infestation could reduce even further the attack density and brood production of spruce beetles, thereby reducing the

potential of an outbreak.

The objective of this study was to test the feasibility of using semiochemicals of secondary scoltyids, in addition to application of formulated MCH, to disrupt or repel attack

by spruce beetle in order to reduce attack densities, gallery development, brood establishment, and survival.

The study, conducted over a 3-year period between 1991 and 1993, consisted of a

trapping experiment using multiple-funnel traps during year one and a felled tree experiment during years two and three. In the trapping experiment, the efficacy of various

pheromones of secondary scolytid species in masking the pheromone of spruce

Materials and

Methods
3

beetles in baited multiple-funnel traps was evaluated. In the felled tree experiments,

the successful semiochemicals from the trapping study along with MCH were tested on

felled uninfested Lutz spruce to determine their efficacy on (1) reducing attractiveness

of spruce beetles to felled host material, and (2) increasing populations of secondary

scolytids, which might compete for limited space and food resources.

Stands of Lutz spruce in the Chugach National Forest, 96 km south of Anchorage,

Alaska, were used for the first year of the experiment (1991). Spruce stands contained

mature trees with less than two infested trees per hectare. Treatments consisted of

four different scolytid semiochemicals: the spruce beetle lure [α-pinene (0.7 mg/day)

plus (R)-(-)-frontalin (0.1 mg/day)]; Dryocoetes affaber [(±)-exo and (±)-endo, 50:50

brevicomin) (0.2 mg/day)]; P. rufipennis [2-methyl-3-buten-2-ol (2.5 mg/day)]; and

I. perturbatus [(±)-ipsdienol (0.2 mg/day)]. All release devices were obtained from

Phero Tech Inc., Delta, British Columbia. Chemical purities, chiralities, and release devices for the spruce beetle lure were as follows: α-pinene, >99 percent pure, (-)-enantiomer, closed polyethylene microcentrifuge tubes; and frontalin >99 percent pure, flex

lures.

Trapping experiments used 12-unit multiple-funnel traps (Lindgren 1983), and an unbaited multiple-funnel trap was used as a control. Traps were hung from a rope suspended between two trees at a height of 2 m and spaced at 30-m intervals. Traps were

hung with the bottom of the collection container 0.3 m from ground level. Traps were

checked weekly and beetles collected and counted. Twelve treatments were replicated

five times in a completely randomized design. Treatment positions were rerandomized

weekly.

The total number of bark beetles caught per species for each of the treatments was

subjected to an ANOVA. Differences between means were tested by using the Tukey

(1953) HSD test at a probability level of P = 0.05.

Stands of Lutz spruce at Quartz Creek and Summit Lake on the Chugach National Forest located on the Kenai Peninsula in south-central Alaska were used for these experiments. Stands with less than two infested trees per hectare were classified as having

low spruce beetle population densities (Summit Lake), whereas stands with more than

six infested trees per hectare were classified as high spruce beetle population densities

(Quartz Creek). Uninfested trees were felled in late April 1992 in a north-south direction

with the crown toward north and were not limbed in order to simulate windthrow and

right-of-way slash.

This experiment used the semiochemicals from all four species of scolytids as well as

the spruce beetle antiaggregation pheromone MCH. Semiochemicals were dispersed

from bubble caps or polyethylene eppendorf tubes. Nine treatments (table 1) were replicated five times on each of the two sites (45 trees per site) in a complete randomized

design. Four sets of semiochemical baits were stapled to the top side of felled trees

and spaced at 4.5-m intervals starting 3.3 m from the butt end of the tree. Unbaited

trees served as controls. Trees were spaced at 50-m intervals.

Treatment effects were evaluated by removing three circular bark samples (100 cm2)

from the top and two sides of each sample tree in the four areas of the bole where the

baits were located. A gas-powered drill equipped with a circular cutting blade was used

to remove bark samples in late July following successful beetle attack and colonization.

Bark disks were placed in zip-lock bags and stored in a freezer at -5 °C until brood and

gallery counts were made.

Chemical Descriptions

Trapping Experiments

Statistical Analysis for

Trapping Experiments

Felled Tree Experiments
4

Table 1—Mean (+ SD) number of scolytids caught in multiple funnel traps by various bark beetle

pheromones alone and in combination in Alaska, 1991a

Treatment D. rufipennis P. rufipennis D. affaber I. perturbatus

Spruce beetle bait 141.8 + 223.8a 0.59 + 1.3b 6.62 + 36.2b 0.00 + 0.0b

(±)-exo/endo-brevicomin 25.7 + 37.7c 0.25 + 0.6b 0.63 + 1.8b 0.06 + 0.2b

Methyl butenol 1.7 + 2.1e 1.16 + 2.3b 16.0 + 32.2a 0.03 + 0.2b

(±)-ipsdienol 24.6 + 41.8c 1.28 + 2.8a 1.28 + 2.7b 0.25 + 0.5b

Spruce beetle bait plus

(±)-exo/endo-brevicomin 55.8 + 68.6b 1.06 + 1.9b 1.25 + 2.0b 0.31 + 0.8b

Spruce beetle bait plus

methyl butenol 28.5 + 44.5c 3.00 + 4.7a 21.00 + 47.8a 0.03 + 0.1b

Spruce beetle bait plus

(±)-ipsdienol 94.2 + 150.6b 0.47 + 1.3b 3.44 + 17.1b 17.97 + 70.4a

Spruce beetle bait plus

(±)-exo/endo-brevicomin plus

methyl butenol 19.2 + 25.0d 0.91 + 1.3b 11.50 + 25.1ab 0.00 + 0.0b

Spruce beetle bait plus

(±)-exo/endo-brevicomin plus

(±)-ipsdienol 30.8 + 60.8c 0.38 + 0.7b 2.12 + 4.4b 0.41 + 0.9b

Spruce beetle bait plus

methyl butenol plus

( ±)-ipsdienol 17.9 + 42.6d 0.44 + 0.7b 13.84 + 24.9ab 0.06 + 0.3b

Spruce beetle bait plus

(±)-exoo/endo-brevicomin plus

methyl butenol plus

(±)-ipsdienol 47.3 + 75.2b 1.59 + 3.4a 22.66 + 53.8a 0.16 + 0.6b

Control 6.7 + 10.4e 0.38 + 0.8b 0.16 + 0.5b 0.03 + 0.2b

a

 Mean values within columns followed by the same letter are not significantly different (P < 0.05, Tukey [1953] studentized range test [HSD]).

This study was repeated in 1993 on stands of Lutz spruce with medium population

densities of spruce beetle (three to four infested trees per hectare) and was located

along Falls Creek Road on the Kenai Peninsula.

Response variables measured for the felled tree experiments included the number of

spruce beetle attacks, number of egg galleries, and number of brood produced. Data

transformation using parametric tests were used for treatments with small sample sizes

and for equal and unequal sample sizes. Means were subjected to ANOVA and the

Newman-Keuls test (P = 0.05) (SAS Institute Inc. 1986).

In the 1991 trapping study using multiple funnel traps, the spruce beetle lure (frontalin

plus α-pinene) tested alone attracted the most spruce beetles. Spruce beetles responded positively to methyl butenol and (±)-ipsdienol but not to (±)-exo- and

(±)-endo-brevicomin when tested alone (table 2). Spruce beetle catch was reduced

by 87 percent when (±)-exo- and (±)-endo-brevicomin plus (±)-ipsdienol, and (±)-exoand (±)-endo-brevicomin plus methyl butenol were added to traps with spruce beetle

lures (table 2). Ips. perturbatus was caught primarily in traps baited with the spruce

beetle bait plus (±)-ipsdienol (table 2). Every bait with (±)-exo- and (±)-endo-brevicomin

attracted D. affaber. Traps baited with (±)-exo- and (±)-endo-brevicomin alone, and

combinations of spruce beetle bait plus (±)-exo- and (±)-endo-brevicomin, and spruce

Statistical Analysis for

Felled Tree Experiments

Results and

Discussion
5

Table 2—Comparison of semiochemicals that induce competition of secondary scolytids with spruce beetles

in felled trees in areas with high and low population densities in Alaska, 1992a

No. of No. of No. of

Treatment beetle attacks beetle galleries beetle brood

High population

Control 0.58 + 0.2d 2.07 + 0.8d 13.27 + 4.9c

Spruce beetle lure 0.47 + 0.2d 1.71 + 0.6c 10.49 + 3.9b

Spruce beetle lure plus

(±)-exo/endo-brevicomin 0.36 + 0.1c 1.73 + 0.6c 12.62 + 6.1c

Spruce beetle lure plus

(±)-ipsdienol 0.38 + 0.2c 1.42 + 0.4b 9.66 + 5.4b

Spruce beetle lure plus

(±)-ipsdienol plus

(±)-exo/endo-brevicomin 0.51 + 0.2d 1.87 + 0.8c 13.42 + 9.5c

Spruce beetle lure plus MCH 0.38 + 0.3c 1.64 + 0.9c 5.47 + 1.8a

Spruce beetle lure plus

(±)-exo/endo-brevicomin plus MCH 0.06 + 0.1a 1.06 + 0.4a 10.03 + 13.5b

Spruce beetle lure plus

(±)-ipsdienol plus MCH 0.18 + 0.2a 1.02 + 0.3a 5.27 + 2.4a

Spruce beetle lure plus

(±)-exo/endo-brevicomin plus

(±)-ipsdienol plus MCH 0.27 + 0.2b 1.24 + 0.7b 8.33 + 6.6b

Low population

Control 0.29 + 0.2b 1.04 + 0.6b 8.53 + 6.7c

Spruce beetle lure plus 0.24 + 0.2b 1.53 + 0.5c 14.42 + 4.5d

(±)-exo/endo-brevicomin 0.16 + 0.2a 2.16 + 0.9d 17.37 + 4.3e

Spruce beetle lure plus

(±)-ipsdienol 0.26 + 0.2b 1.69 + 1.2c 13.20 + 9.2d

Spruce beetle lure plus

(±)-ipsdienol plus

(±)-exo/endo-brevicomin 0.18 + 0.3a 1.16 + 0.7b 9.45 + 9.4c

Spruce beetle lure plus MCH 0.13 + 0.1a 0.69 + 0.5a 4.49 + 3.3b

Spruce beetle lure plus

(±)-exo/endo-brevicomin plus MCH 0.24 + 0.2b 0.1.11 0.9b 5.96 + 4.2b

Spruce beetle lure plus

(±)-ipsdienol plus MCH 0.18 + 0.2a 1.24 + 0.8b 11.22 + 8.8c

Spruce beetle lure plus

(±)-exo/endo-brevicomin plus

(±)-ipsdienol plus MCH 0.11 + 0.1a 0.56 + 0.5a 2.49 + 2.6a

a

 Spruce beetle population density, low <2, high >6 infested trees per hectare. Mean values within columns followed by the same letter are not

significantly different (P < 0.05, Tukey [1953] standardized range test [HSD]).
6

beetle bait plus (±)-exo- and (±)-endo-brevicomin plus methyl butenol and (±)-ipsdienol

caught the highest number of D. affaber (table 1). An insignificant number of P.

rufipennis adults were attracted to traps baited with the semiochemicals when tested

alone or in various combinations.

It appears that dispersing spruce beetles are repelled when they come into contact with

pheromones from secondary scolytids; a chemical message possibly indicating a colonized host. Conversely, the addition of the spruce beetle bait to (±)-exo- and (±)-endobrevicomin and to (±)-ipsdienol increased trap catches of the competing secondary

scolytids, except P. rufipennis (table 1). These secondary species are apparently keying into the pheromone of spruce beetle as an indicator of potential host material (e.g.,

a spruce beetle infested tree).

The study continued in 1992 in stands of Lutz spruce with low and high population densities of spruce beetles. The number of spruce beetle attacks, beetle galleries, and

brood were compared among felled green trees baited with the spruce beetle baits and

various combinations of (±)-ipsdienol, (±)-exo- and (±)-endo-brevicomin, and MCH. The

addition of pheromones from secondary scolytid species or MCH significantly reduced

attack densities of spruce beetles in stands with both high and low population densities

(table 2). The largest significant reduction in attack density and brood production of

spruce beetle, for both study sites, was obtained when a combination of (±)-exo- and

(±)-endo-brevicomin plus MCH was added to trees with the spruce beetle baits. The

addition of either (±)-exo- and (±)-endo-brevicomin plus MCH, or (±)-ipsdienol plus

MCH to trees baited with spruce beetle lures reduced attack density by 87 percent and

62 percent, respectively, in stands with high populations of spruce beetles (table 2).

The addition of MCH to trees baited with spruce beetle lures plus (±)-ipsdienol reduced

gallery construction by 40 percent and brood production by 50 percent in high populations (table 2). In low and medium populations of spruce beetles, the addition of (±)-

exo- and (±)-endo-brevicomin plus (±)-ipsdienol and MCH to trees baited with spruce

beetle lures disrupted gallery construction by 63 percent (low population) and 77 percent (medium) and brood production by 83 percent (low) and 81 percent (medium

population) (tables 2 and 3).

When populations of spruce beetles were high, numbers of galleries and brood production were significantly lower (table 2). This could have been caused by increased competition from secondary scolytid species. Combinations of the spruce beetle baits plus

MCH, and the spruce beetle baits plus (±)-ipsdienol plus MCH resulted in the least

number of spruce beetle brood produced. At low densities of spruce beetles, the lowest

numbers of brood as well as the lowest attack densities were found on trees baited with

(±)-exo- and (±)-endo-brevicomin plus (±)-ipsdienol and MCH. The high variability of

the data for brood density, however, suggests that low numbers of brood could be an

artifact. The addition of MCH to trees with spruce beetle baits and those trees baited

with pheromones from secondary scolytid species repelled spruce beetle attack.

The results of the 1993 field test (table 3) conducted in stands with medium populations of spruce beetles showed similarities as well as differences to the previous two

studies. The addition of (±)-ipsdienol, and combinations of (±)-ipsdienol plus MCH,

(±)-exo- and (±)-endo-brevicomin plus MCH, and (±)-exo- and (±)-endo-brevicomin

plus (±)-ipsdienol and MCH to trees with spruce beetle baits reduced the number of

spruce beetle attacks. Again, the addition of (±)-exo- and (±)-endo-brevicomin plus

(±)-ipsdienol and MCH to trees with spruce beetle baits resulted in the highest reduction of spruce beetle attacks, gallery construction, and brood production (table 3).
7

This treatment caused additional reductions in attacks and brood production of 40 and

52 percent, respectively, compared with the addition of MCH alone. The addition of

(±)-exo- and (±)-endo-brevicomin and (±)-exo- and (±)-endo-brevicomin plus (±)-

ipsdienol to spruce beetle baited trees had no effect on the parameters measured in

stands with medium spruce beetle population levels, unlike the low population results

(tables 2 and 3).

The results from these field experiments indicate that the use of the spruce beetle

antiaggregant MCH in conjunction with pheromones from secondary scolytids can be

used to significantly reduce spruce beetle attack, gallery construction, and brood levels

in felled, susceptible host trees. This could prevent potential colonization of standing

trees and subsequent initiation of a large spruce beetle infestation.

We thank Robert Wolfe, Ken Zogas, Vaughn Salisbury, Curtis Stigall, and John Hard

of Forest Health Management, State and Private Forestry, Alaska Region, Anchorage,

Alaska, for felling the trees, collecting bark samples, and counting beetles. We also

thank Tim Max, Pacific Northwest Research Station, Portland, Oregon, for help in statistical analysis of the data.

Table 3—Comparison of semiochemicals that induce competition of secondary scolytids with spruce beetles

in felled trees in areas with medium population densities in Alaska, 1993a

No. No. No.

Treatment beetle attacks beetle galleries beetle brood

Control 0.40 + 0.5c 1.00 + 0.9d 17.73 + 11.9c

Spruce beetle lure 0.47 + 0.4c 0.95 + 0.5d 15.67 + 4.7c

Spruce beetle lure plus

(±)-exo/endo-brevicomin 0.95 + 0.7d 1.82 + 0.7e 25.90 + 14.1d

Spruce beetle lure plus

(±)-ipsdienol 0.09 + 0.2a 0.36 + 0.4b 13.27 + 7.9c

Spruce beetle lure plus

(±)-exo/endo-brevicomin plus

(±)-ipsdienol 0.44 + 0.5c 1.05+ 0.6d 16.84 + 8.4c

Spruce beetle lure plus MCH 0.22 + 0.4b 0.60 + 0.7c 6.29 + 5.8b

Spruce beetle lure plus

(±)-exo/endo-brevicomin plus

 MCH 0.07 + 0.2a 0.35 + 0.4b 7.40 + 7.6b

Spruce beetle lure plus

(±)-ipsdienol plus MCH 0.11 + 0.2a 0.35 + 0.5b 6.67 + 7.7b

Spruce beetle lure plus

(±)-exo/endo-brevicomin plus

(±)-ipsdienol plus MCH 0.13 + 0.3a 0.22 + 0.3a 2.98 + 4.4a

a

 Medium spruce beetle population density is <2 infested trees per hectare. Mean values within columns followed by the same letter are not

significantly different (P < 0.05, Tukey [1953] studentized range test [HSD]).

Conclusions

Acknowledgments
8

When you know: Multiply by: To find:

Celsius (°C) 1.8 and add 32 Fahrenheit

Square centimeters (cm2) 2.54 Inches

Hectares (ha) 2.47 Acres

Kilometers (km) 0.621 Miles

Meters (m) 3.281 Feet

Milligrams (mg) 0.001 Ounces

Millimeters (mm) 0.254 Inches

Berryman, A.A. 1974. Dynamics of bark beetle populations: towards a general

productivity model. Environmental Entomology. 3: 579-585.

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English Equivalents

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