United States 

Department o 

Agriculture 

Forest 

Service 

Northern 

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

 

Report 03-9 June 2003 

A TEST OF VERBENONE TO PROTECT INDIVIDUAL WHITEBARK PINE 

FROM MOUNTAIN PINE BEETLE ATTACK 

Sandra Kegley, Ken Gibson, John Schwandt, and Michael Marsden 

Abstract 

In the Selkirk Mountains of northern Idaho, 

individual whitebark pine trees baited with an 

attractant pheromone were protected from mass 

attack by mountain pine beetles. Using either 

two or four verbenone pouches per tree, mass 

attacks on treated trees were significantly less 

than those on controls. This test provides strong 

evidence that individual trees can be protected 

from mountain pine beetle attack using 

verbenone. 

Introduction 

Whitebark pine (Pinus albicaulis Engelm.), one 

of a few species that grow in the subalpine 

community, plays a key role in survival and 

distribution of wildlife species, is important in 

watershed stabilization, and for recreation and 

aesthetic values. This key species is currently in 

rapid decline due to a variety of factors including 

the introduced white pine blister rust fungus, fire 

suppression, forest successional processes, and 

periodic outbreaks of mountain pine beetle 

(Dendroctonus ponderosae Hopkins) (MPB) 

(Keane and Arno 1993). 

The Selkirk Mountains contain the largest, most 

continuous whitebark pine population remaining 

in northern Idaho. Blister rust has been slowly

killing or top killing trees there for many years 

and a current MPB outbreak has killed more 

than 64 percent of the remaining whitebark pine 

in some stands (Kegley et al. in prep). These 

whitebark pine forests are relatively dense with 

subalpine fir, spruce, and lodgepole pine as 

competing species (Kegley et al. 2001) (figure 

1). Few openings exist for whitebark pine 

regeneration. The Bonners Ferry Ranger 

District is planning to create openings for 

regeneration with prescribed fire. In the 

meantime, there is a great need to protect 

remaining whitebark pine trees from MPB attack 

to ensure an adequate seed source for 

regeneration. 

While individual, high-value trees can be 

protected from beetle attack with insecticides 

sprayed on tree boles with high-pressure spray 

equipment, this not practical in inaccessible 

areas or on a large scale. Verbenone 

(4,5,5-trimethylbicyclo [3.1.1] hept-3-en-2-one), 

a natural anti-aggregation pheromone of MPB,
2 

has been tested as a tree protectant in the past 

with inconsistent results (Amman et al. 1991, 

Amman and Lindgren 1995, Bentz et al. 1989, 

Gibson and others 1991, Shore et al. 1991). A 

new “pouch” formulation, releasing 10 times as 

much verbenone as past releasers, has recently 

been developed (Phero Tech Inc.), tested with 

promising results in lodgepole pine stands 

(Progar In press), and is currently registered for 

use against southern pine beetle (D. frontalis

Zimmerman). It significantly reduced numbers 

of beetle-attacked trees in 1-acre treated blocks 

of lodgepole and whitebark pine (Bentz et al. 

2002). Our objective for this experiment was to 

test the verbenone pouch as an individual tree 

protectant. 

Methods 

The test was conducted in the Selkirk 

Mountains, Bonners Ferry Ranger District, Idaho 

Panhandle National Forest. A total of 146 

whitebark pine trees were randomly assigned 

one of the following treatments: 1) control, no 

verbenone, 2) 2 verbenone (2V) pouches on 

individual trees, or 3) 4 verbenone (4V) pouches 

on individual trees. Trees were located at least 

130 feet apart. In addition to verbenone 

pouches, every tree in the test was baited with 

an attractant pheromone (MPB tree bait, Phero 

Tech, Inc.) to assure equal beetle pressure. 

Figure 1. Whitebark pine killed by MPB in the 

Selkirk Mountains. 

In September, following beetle flight, all treated 

trees were evaluated for presence of mass 

attacks, strip attacks, and pitchouts. Diameter at 

breast height (d.b.h.) and blister rust condition 

was also recorded for each tree. Blister rust 

information was recorded as low, when only old 

dead branches were observed; moderate on 

trees with current flagging; or severe when trees 

had bole cankers. Tree baits were stapled to 

the north side of trees. Verbenone pouches 

were stapled in the four cardinal directions on 

4V-treated trees or on the east and west sides of 

2V-treated trees. Because of an apparently long 

flight period of MPB in whitebark pine (Kegley et 

al. in prep), trees were selected and treated the 

first week in June; and verbenone pouches were 

replaced at the end of July. Due to the snow 

depth, initial pheromones were placed 10-15 

feet high on tree boles. Replacements were 

about 7-8 feet high on tree boles (figure 2). 

Figure 2. Vergbenone pouches stapled to a 

white bark pine tree. 

Statistical Analysis 

Numbers of trees with no beetle attack, mass 

attack, strip attack, and pitchouts were 

summarized by treatment. The Pearson ChiSquare test was used to test for significant 

differences in the type of MPB attack between 

treatments. Logistic regression analysis was 

used to determine the effect of d.b.h., presence 

of blister rust infection and degree or severity of 

blister rust on the probability of mass attack, 

strip attack, pitch out, or any of the above MPB 

attacks. 
3 

Results 

Numbers and percent of trees by type of MPB 

attack are summarized in table 1 and figure 3. 

Significantly more mass attacks occurred in the 

control trees (Pearson chi-square test, p< 0.001) 

than either the 2V treatment or the 4V treatment. 

There was no significant difference between 2V 

and 4V treatments. 

Table 1. Number and percent of trees with pitch outs, strip attacks, mass attacks, or no MPB attack by 

treatment. 

Treatment/ 

MPB status 

Control 

Number/percent 

2V treatment 

Number/percent 

4V treatment 

Number/percent 

No attack 0 18 38% 17 34% 

Pitch out 0 18 38% 19 38% 

Strip attack 0 7 15% 11 22% 

Mass attack 48 100% 5 10% 3 6% 

N (total) 48 48 50 

Figure 3. MPB attack by treatment 

0%

20%

40%

60%

80%

100%

Control 2 V 4V

Treatment

% Trees

mass attack

strip attack

pitch out

No attack
4 

Average d.b.h. of all trees in this test was 20.3 

inches and was not statistically different 

between treatments (Analysis of Variance F-test, 

p>.08) (table 2). 

Table 2. Average d.b.h. by treatment 

Treatment Average tree diameter 

C 19.1 

2V 20.8 

4V 20.9 

Because all control trees were mass-attacked, 

only trees treated with verbenone were analyzed 

for relationship between MPB attack and d.b.h., 

and between MPB and incidence and severity of 

blister rust. This reduced our sample size from 

146 trees to 98 trees for this analysis. 

Logistic regression was used to model the type 

of attack by MPB as a function of d.b.h., the 

degree of blister rust infection, and the presence 

of blister rust. Diameter at breast height and the 

presence of blister rust were found to be 

significant in the prediction of any MPB attack. 

The probability of attack by MPB increased as 

d.b.h. increased (Wald test of coefficients, 

p< .001) and was significantly greater on 

uninfected trees than on trees with blister rust 

infection (Wald test of coefficients, p< .05) 

(figure 4). However, no significance was found 

when the type of beetle attack or intensity of rust 

infection was defined in more detail (mass 

attack, strip attack, pitchout, or light, moderate, 

severe rust infection) 

Figure 4. Prediction of MPB attack based on d.b.h. PREDATT1=probability of any MPB attack. Upper 

line is the prediction of MPB attack on trees with no blister rust. The lower line is the 

prediction on trees infected with any blister rust (branch or bole cankers). 
5 

Discussion and Conclusions 

This test provides strong evidence that 

verbenone can protect individual whitebark pine 

trees from MPB attack, even when trees are 

baited with an attractant pheromone. Although 

verbenone pouches show great promise in 

protecting individual trees, further testing in 

different areas is needed before the product 

registration is extended to include MPB and can 

be recommended for operational use. 

The probability of attack by MPB increases as 

d.b.h. increases. Beetles also appear to prefer 

trees that are not infected with blister rust, 

although this relationship should be tested 

further. It is not likely that a blister rust branch 

canker on a large tree would have any affect on 

MPB behavior. But it is logical that a bole 

canker resulting in top-kill may predispose trees 

to MPB attack, especially when MPB 

populations are low. However, we found no 

significant relationship between severely 

infected trees and MPB attack in our test. In a 

study in Montana, MPB did prefer whitebark pine 

trees with higher blister rust infection levels 

(Adams and Six 2002). The use of pheromones 

in our study may have influenced the 

relationship, but all the trees we analyzed for 

rust and MPB interactions were treated similarly-

-with both verbenone and an attractant 

pheromone. No clear relationship was found 

between blister rust and MPB in other whitebark 

stands surveyed in northern Idaho that were not 

involved in the use of pheromones (Kegley et al. 

2001). It is also possible that the influence of 

blister rust on MPB attack may be different when 

MPB populations are at low levels than at 

outbreak levels. More data is needed to clearly 

define any relationship between MPB and blister 

rust in whitebark pine. 

Acknowledgements 

We thank Jill Wilson for assistance in identifying 

and treating test trees and Gary Kempton for 

assisting in data collection. The USDA Forest 

Service Forest Health Protection Special 

Technology Development Program funded this 

project. 

Literature Cited 

Adams, J. and D. Six. 2002. Effect of white pine 

blister rust infection on mountain pine beetle 

preference in whitebark pine. Poster 

presented at NSF-Train Program, Univ. of 

Montana, Missoula, MT, Sept. 12, 2002. 

Amman, G.D., R.W. Their, J.C. Weatherby, L.A. 

Rasmussen, and A.S. Munson. 1991. 

Optimum dosage of verbenone to reduce 

infestation of mountain pine beetle in 

lodgepole pine stands of central Idaho. 

USDA Forest Service, Research Paper INT446. 

Amman, G.D., and B.S. Lindgren. 1995. 

Semiochemicals for management of 

mountain pine beetle: status of research and 

application, pp. 14-22. In Salom and Hobson 

(eds.), Application of semiochemicals for 

management of bark beetle infestationsProceedings of an informal conference, 

USDA Forest Service, INT-GTR-318. 

Bentz, B.J., C.K. Lister, J.M. Schmid, S.A. Mata, 

L.A. Rasmussen, D. Haneman. 1989. Does 

verbenone reduce mountain pine beetle 

attacks in susceptible stands of ponderosa 

pine. USDA For. Serv. Res. Note RM-495. 

Bentz, B.J., S.J. Kegley, K.E. Gibson, and R. 

Their. 2003. In press. A test of nonhost tree 

volatiles and verbenone for reducing the 

number of mountain pine beetle-attacked 

trees. RMRS Rpt. 

Gibson, K.E, R.F. Schmitz, G.D. Amman, and 

R.D. Oakes. 1991. Mountain pine beetle 

response to different verbenone dosages in 

pine stands of western Montana. USDA 

Forest Service, Res. Pap. INT-444. 

Keane, R.E., and S.F. Arno. 1993. Rapid decline 

of whitebark pine in Western Montana: 

Evidence from 20-year remeasurements. 

Western Journal of Applied Forestry 8(2): 

44-47 
6 

Kegley, S.J., J.W. Schwandt, and K.E.Gibson. 

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whitebark pine on Pyramid Pass, Russell 

Mountain, and Burton Ridge in the Selkirk 

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Rpt. 01-8. 11 p. 

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mountain pine beetle. USDA For. Serv. 

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