United States 

Department o 

Agriculture 

Forest 

Service 

Northern

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

Report 04-7 March 2004

TESTING THE EFFICACY OF VERBENONE IN REDUCING

MOUNTAIN PINE BEETLE ATTACKS IN SECOND-GROWTH PONDEROSA PINE

Ken Gibson1

 and Sandy Kegley2

Abstract range from Canada to Mexico. In the Northern 

Region alone, from the 1960’s to the mid-1980’s 

about 250 million host trees were killed on more 

than 3 million acres. While approximately 90% 

of those were lodgepole pines, a significant 

amount of ponderosa pines were also killed. 

“Standard” and “new,” 5-gram verbenone 

pouches were placed in a grid throughout oneacre treatment plots in a second-growth 

ponderosa pine stand on the Helena National 

Forest (NF). Lower than anticipated mountain 

pine beetle (MPB) populations resulted in 

difficult-to-assess treatment affects; however, it 

appeared there were differences in the behavior 

of the two pouches. By replacing the standard 

pouch midway through beetle flight, we achieved 

a treatment affect different from both the new 

pouch and controls. Latter two treatment affects 

were similar. Additional testing will be required 

of the new pouch before we can conclude its 

elution period is significantly longer, and more 

effective, than the standard. 

Management options for reducing mortality 

caused by MPB include changing stand 

conditions through silvicultural practices, beetle 

population manipulation with commercially 

available attractant pheromones, and removal of 

infested trees (Samman and others 2000). 

Individual protection of high value trees with 

chemical treatments is not practical on a large 

scale or in inaccessible areas. Because many 

areas of varied resource concerns preclude stand 

manipulations to reduce MPB-caused mortality, 

there has long been interest in evaluating the 

effectiveness of anti-aggregation compounds as 

tree or stand protectants. 

Introduction

Mountain pine beetle (Dendroctonus ponderosae

Hopkins) is the most destructive bark beetle in 

western North America. It is capable of killing 

most pine species over large areas throughout its 

Verbenone (4,6,6-trimethylbicyclo[3.1.1]hept-3-

en-2-one), a semiochemical apparently produced 

by both male and female beetles, has exhibited 

1

Forest Health Protection, Missoula Field Office 2

 Forest Health Protection, Coeur d’Alene Field Office 
design, replicated 6 times, was used to test for 

differences among treatments. Each block 

consisted of three 1-acre plots separated by at 

least 2.5 chains (165 feet). 

promising anti-aggregative effects. In early 

tests, it was shown to inhibit the response of 

MPB (Ryker and Yandell 1983). When 

synthetically produced verbenone was added to 

funnel traps baited with MPB attractants (transverbenol, exo-brevicomin, and myrcene), beetle 

catches were reduced significantly from traps 

with attractant alone (Borden and others 1987, 

Miller and others 1998, Schmitz and McGregor 

1990). 

Each plot in a block received one of three 

treatments: 1) control (no pouches), 2) 

“standard” 5-gram verbenone pouch, and 3) 

“new” verbenone 5-gram pouch. Both pouches 

were made by Phero Tech, Inc.; but had been 

manufactured with differing membrane 

thickness, the intent being to produce different 

elution rates and periods. The “standard” pouch 

(membrane thickness 1.5 ml) was formulated to 

elute over a 25-40 day period. The “new” pouch 

(membrane thickness 3.0 ml) was anticipated to 

have a longer, 60-90 day, elution period. 

Treatments were randomly assigned to each plot 

within a block. For “new” verbenone treatments, 

40 pouches were placed within each plot on a 

0.5- x 0.5-chain (33 feet) grid. Earlier tests had 

concluded there was no significantly different 

treatment affect between 20 and 40 standard 

pouches per acre (Bentz, and others, 2004). 

Therefore, in the “standard” treatment, 20 

pouches were placed in each plot on an 

approximate 45- x 45-feet grid. Individual 

pouches were stapled to the north side of the tree 

nearest intersecting grid point, about 6 feet from

the ground. 

Field tests conducted during the late-1980’s, 

however, using commercially available 0.5-gram

verbenone bubble capsules (Phero Tech, Inc.) in 

an effort to protect stands from MPB attack were 

inconsistent (Amman and others 1991, Amman 

and Lindgren 1995, Bentz and others 1989, 

Gibson and others 1991, Shore and others 1991). 

In recent years, similar studies using 5-gram

verbenone pouches, which release 10 times the 

amount of verbenone as bubble capsules, have 

shown promising results (Bentz, and others, 

2004; Progar 2003; Borden, and others, 2003). 

Currently, MPB populations are at epidemic 

levels throughout the intermountain West. This 

is, therefore, an opportune time to test varying 

strategies—including new formulations of 

verbenone—for protecting high-value stands 

from MPB-caused mortality. Our objective in 

this test was to compare the effectiveness of a 

new, purportedly longer-lasting verbenone pouch 

(3 ml-thick membrane) with the standard (1.5 ml

thickness), 5-gram pouch in protecting 

ponderosa pine stands from MPB attack. 

In an attempt to assure equal beetle pressure in 

each plot, we placed a Lindgren funnel trap, 

baited with standard MPB pheromone lures 

(PheroTech, Inc), at the center of each plot. All 

compounds and baited funnel traps were 

installed on June 23-24, prior to beetle flight. 

Because of their registered elution period of 25-

40 days, “standard” pouches were replaced at the 

end of July. 

Methods

The study site, a second-growth ponderosa pine 

stand on the Helena Ranger District (RD), 

Helena NF, was selected in June 2003 in an area 

not far from active MPB populations. Stands 

were predominantly ponderosa pine, with lesser 

amounts of Douglas-fir, aspen, and cottonwood 

in some plots. Although number of susceptible 

ponderosa pine varied somewhat from plot to 

plot, stocking was similar in most. Stocking 

varied from a low of 69 square feet per acre to 

high of 156; most—14 of 18 plots—were 

between 100 and 143 square feet per acre 

(Appendix, Table 1). A randomized block 

In order to evaluate elution periods of both 

pouches, we placed six of each on a tree outside 

the test area, but close enough for environmental 

conditions to be similar. One of each type pouch 

was removed at 2-week intervals, quickly placed 

in a freezer, then analyzed for content at the end 

of the season. Close by, we also installed a 

“Hobo” temperature-recording device to help us 

correlate pouch elution with daily temperatures 

in the area. 

2 
attacked trees (2 [0.19%]) compared to controls 

(14 [1.78%]) and “new” verbenone treatment (16 

[2.19%]) (p=0.05); MPB attacks in the “new” 

verbenone treatment plots were actually higher 

(although not significantly) than in controls. 

Still, numbers of new attacks in combined 

treatments (32 in 18 plots) were sufficiently low 

that we are less confident in the meaningfulness 

of treatment affects. 

Following beetle flight (September 15-16), all 

trees equal to or greater than 5 inches diameterat-breast-height (d.b.h.) were tallied. For each 

tree, we recorded d.b.h., species, and infestation 

status. Status categories included: 1) live tree, 

2) 2003 MPB “mass” attack, 3) 2002 MPB 

“mass” attack, 4) 2003 MPB “strip” attack, and 

5) 2003 “unsuccessful” MPB attack (Appendix, 

Table 2). 

Data Analysis Basal area calculations (Table 1) revealed 

substantial differences in plot density. Plots with 

“standard” pouches averaged 101 square feet per 

acre basal area, plots with “new” pouches 124, 

and control plots 134. The plots with the most 

new attacks (5 each) were two of the more 

densely stocked. Plot #11 had basal area of 142 

while basal area of plot #12 was 146. Had beetle 

populations been higher, those analyses may 

have been significant. As it was, all new attacks 

were found within about ten feet of the baited 

funnel trap. That would seem to negate any 

influence associated with stand density. 

For data analysis, trees were regarded as 

“attacked” (including 2003 mass attacks and 

2003 strip attacks), or “not attacked” (including 

unattacked and unsuccessfully attacked trees). 

Those were variables associated with treatment 

(control, “standard” pouch, “new” pouch) 

affects. Tree d.b.h., species, and stand stocking 

were variables not affected by treatments. 

The Univariate analysis of variance was used to 

detect treatment affects. The ratio of the number 

of successfully attacked trees to the total number 

of possible trees to be attacked was the criteria of 

these analyses. Data were transformed using the 

arc sin of the square root of the proportion to 

satisfy requirements of the test. Differences 

between treatments were tested using the Least 

Significant Difference (LSD) test. 

Pouch Analysis: 

Pouch analysis (John Borden, Phero Tech, 

personal communication) showed differences in 

residual verbenone and elution rates over time

(Table 3). 

Results and Discussion Analysis showed the standard pouch released a 

higher amount of verbenone per day, which 

appears to have resulted in a shorter elution 

period. In addition, pouch analysis indicated, in 

the field, virtually no verbenone was eluted 

below a residual amount of 2 grams. That does 

not occur in the laboratory, and is somewhat 

perplexing to Phero Tech chemists (John 

Borden, personal communication). That being 

the case, standard pouches would have ceased 

releasing verbenone by about mid-August—

before beetle flight was over. That would lend 

credence to our supposition that standard 

pouches should be replaced after several weeks 

in the field; and might also explain why we 

seemed to have better results in this test with the 

standard pouch—which was replaced at midseason

Verbenone Effectiveness: 

Individual plots within the study site represented 

a range of host availability and stand density 

(Appendix, Tables 1 and 2). MPB populations, 

as measured by the number of infested trees in 

2002, were found in only three plots; and in 

hindsight, perhaps were not adequate for the 

purposes of our evaluation. New (2003) attack 

rates in all plots were low; however, despite low 

numbers of successful attacks; significant 

differences did occur between treatments. 

While the “standard” verbenone treatment 

significantly reduced the number of beetle3 
Table 3. Residual Verbenone and Calculated Elution Rate, June 24-August 26, 2003. 

(Pouches contained 4.65 grams verbenone when installed.) 

Date (placed 

June 24, 2003) 

Residual Verb. 

New (gms) 

Residual Verb 

Std (gms) 

Elution rate 

New (mg/day) 

Elution rate 

Std (mg/day) 

8 July 4.44 4.05 15 43 

22 July 3.83 2.92 43 80 

5 Aug 3.44 2.39 28 38 

16 Aug 3.01 1.81 39 53 

26 Aug 2.93 1.90 8 0* 

*Indicates pouch had ceased eluting verbenone

Temperature Recordings: replacement, provided better tree protection than 

a single application of the “new” pouch. 

Data readings from the “Hobo” temperature 

recorder showed unusually high daily maximum 

temperatures for the test period (Figure 1). 

Seventeen days were 90 degrees or higher; 36 

were 85 degrees or higher. We believe these 

atypical conditions may have been responsible 

for the relatively short elution period 

experienced by the “standard” pouch, and why 

we got better results with pouch replacement in 

those plots. 

Temperature recordings also suggested unusually 

high temperatures during July and August may 

result in shorter than anticipated elution periods 

from either pouch. Presently, it appears neither 

pouch, in a single application during a warmerthan-normal year, can provide adequate 

protection for the period 

typically experienced for MPB 

flights in ponderosa pine stands 

in our Region (mid-July to lateAugust). Our data suggested for 

low-elevation, warmer sites, 

protection from MPB attacks 

may be achieved using the 

standard 5-gram verbenone 

pouch; but in warmer years, it 

would have to be replaced after 

5-6 weeks in the field. 

Figure 1. Daily Maximum Temperature

24 June - 23 September

0

20

40

60

80

100

120

6/24/2004

7/1/2004

7/8/2004

7/15/2004

7/22/2004

7/29/2004

8/5/2004

8/12/2004

8/19/2004

8/26/2004

9/2/2004

9/9/2004

9/16/2004

9/23/2004

Date

Temperature

Acknowledgments 

We thank Tim Cudmore, Curtis 

Johnson, Sherri Welch, Gary Kempton, and 

Doug Wulff for assistance in the field. Mike 

Marsden provided statistical analysis. Larry 

Stipe provided GIS support and project maps. 

The project was funded by Special Technology 

Development Program, Forest Health Protection, 

Washington Office. 

Conclusion 

In hindsight, MPB populations were marginally 

low to conduct the 2003 test in the area we did. 

However, beetle response to treatments 

suggested the “standard” pouch, with 

4 
References Cited 

Amman, G.D.; Thier, R.W.; Weatherby, J.C.; 

Rasmussen, L.A.; Munson, A.S. 1991. 

Optimum dosage of verbenone to reduce 

infestation of mountain pine beetle in 

lodgepole pine stands of central Idaho. 

Research Paper INT-446. Ogden, UT: 

USDA Forest Service, Intermountain Forest 

and Range Experiment Station. 5p. 

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

Semiochemicals for management of 

mountain pine beetle: status of research and 

application. In: Salom and Hobson (eds.), 

Application of semiochemicals for 

management of bark beetle infestationsProceedings of an informal conference. Gen. 

Tech. Report. INT-GTR-381. Ogden, UT: 

USDA Forest Service, Intermountain Forest 

and Range Experiment Station. p 14-22. 

Bentz, B.J.; Lister, C.K.; Schmid, J.M.; Mata, 

S.A.; Rasmussen, L.A.; Haneman, D. 1989. 

Does verbenone reduce mountain pine beetle 

attacks in susceptible stands of ponderosae 

pine. Research Note RM-495. Ft. Collins, 

CO: USDA Forest Service, Rocky Mountain 

Forest and Range Experiment Station. 4p. 

Bentz, B.J.; Kegley, S.J.; Gibson, K.E.; Thier, 

R.. 2004. A test of nonhost volatiles and 

verbenone for reducing the number of 

mountain pine beetle-attacked trees. In 

preparation. 

Borden, J.H.; Ryker, L.C.; Chong, L.J.; Pierce, 

H.D.; Johnston, B.D,; Oehlschlager, A.C. 

1987. Response of the mountain pine beetle, 

Dendroctonus ponderosae Hopkins 

(Coleooptera: Scolytidae), to five 

semiochemicals in British Columbia 

lodgepole pine forests. Canadian Journal of 

Forest Research. 17:118-128. 

Borden, J.H.; Chong, L.J.; Earle, T.J.; Huber, 

D.P.W. 2003. Protection of lodgepole pine 

from attack by the mountain pine beetle, 

Dendroctonus ponderosae (Coleoptera: 

Scolydtidae) using high doses of Verbenone 

in combination with nonhost bark volatiles. 

The Forestry Chronicle 79:3:685-691. 

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

Oakes, R.D. 1991. Mountain pine beetle 

response to different verbenone dosages in 

pine stands of western Montana. Research 

Paper INT-444. Odgen, UT: USDA Forest 

Service, Intermountain Forest and Range 

Experiment Station. 11p. 

Miller, D.R.; Borden, J.H.; Lindgren, B.S. 1995. 

Verbenone: Dose-dependent interruption of 

pheromone-based attraction of three 

sympatric species of pine bark beetles 

(Coleoptera: Scolytidae). Environmental 

Entomology 24(3):692-696. 

Progar, R.A. 2003. Verbenone reduces 

mountain pine beetle attack in lodgepole 

pine. Western Journal of Applied Forestry 

18(4):229-232. 

Ryker, L.C.; Yandell, K.L. 1983. Effect of 

verbenone on aggregation of Dendroctonus 

ponderosae (Coleoptera: Scolytidae) to 

synthetic attractant. Zeitschrift fur 

Angewandte Entomologie 96: 452-459. 

Samman, S.; Logan, J.A. (Eds.). 2000. 

Assessment and response to bark beetle 

outbreaks in the Rocky Mountain Area. Gen. 

Tech. Report GTR-62. Ft. Collins, CO: 

USDA Forest Service, Rocky Mountain 

Research Station. 46p. 

Schmitz, Richard F.; McGregor, Mark D. 1990. 

Antiaggregative effect of verbenone on 

response of the mountain pine beetle to 

baited traps. Research Paper INT-423. 

Ogden, UT: USDA Forest Service, 

Intermountain Research Station. 7 p. 

Shore, T.L.; Safranyik, L; Lindgren, B.S. 1991. 

The response of mountain pine beetle 

(Dendroctonus ponderosae) to lodgepole 

pine trees baited with verbenone and exobrevicomin. Journal of Chemical Ecology 

18(4):533-541.

5 
Appendix 

Table 1. Stand Characteristics of Test Plots 

Plot 

Pre-Test 

Green PP 

> 5” d.b.h. 

Average 

d.b.h. 

Other spp. 

> 5” d.b.h.

Live 

BA per 

Acre 

Live 

Trees per 

Acre 

2002 

MPB 

Attacks 

1 205 11.0 8 141 213 5

2 166 11.1 16 122 182 0

3 162 10.1 56 125 218 0

4 146 11.2 84 143 230 0

5 174 10.0 98 82 272 0

6 119 9.2 102 112 221 2

7 68 12.0 33 69 101 0

8 97 14.6 24 128 121 0

9 169 11.7 22 142 191 0

10 143 13.2 40 156 183 0

11 118 13.3 50 143 168 0

12 121 14.1 16 146 137 0

13 89 13.8 17 101 106 0

14 102 12.9 20 114 122 0

15 59 14.0 86 123 145 0

16 116 12.7 9 109 125 1

17 105 12.9 19 111 124 0

18 110 11.8 8 90 118 0

6 
Table 2. Verbenone Test Results (All Plots) 

Plot 

Number 

Treatment 

PP > 5” 

Not 

Attacked 

Mass 

Attack 

Strip 

Attack Pitchout

2002 

Attack 

(Faders) 

Percent 

2003 

Attack 

1 Control 194 2 0 9 5 0.97

2 Standard 164 1 0 1 0 0.60

3 New 159 0 0 3 0 0

4 Control 142 1 0 3 0 0.68

5 Standard 172 1 0 1 0 0.57

6 New 111 4 0 4 2 3.36

7 Standard 68 0 0 0 0 0

8 Check 94 2 0 1 0 2.06

9 New 163 2 1 3 0 1.78

10 Control 138 4 0 1 0 2.79

11 New 111 5 0 2 2 4.23

12 Control 114 5 0 2 0 4.13

13 Standard 89 0 0 0 0 0

14 New 102 0 0 0 0 0

15 Standard 59 0 0 0 0 0

16 Standard 110 0 0 6 0 0

17 New 97 3 1 4 0 3.80

18 Control 110 0 0 0 0 0

Table 2a. Test Results: Control Plot Averages 

Plot Number 

(C) 

Green PP > 5” 

d.b.h. 

Total Trees 

per Acre 

2003 

Attacks 

% 2003 

Attacks 

1 205 213 2 0.97

4 142 230 1 0.68

8 94 121 2 2.06

10 138 183 4 2.79

12 114 137 5 4.13

18 110 118 0 0

Average 132 167 2.33 1.78

7 
8 

Table 2b. Test Results: “Standard” Plot Averages 

Plot Number 

(S) 

Green PP > 5” 

d.b.h. 

Total Trees 

per Acre 

2003 

Attacks 

% 2003 

Attacks 

2 166 182 1 0.60 

5 174 272 1 0.57 

7 68 101 0 0 

13 89 106 0 0 

15 59 145 0 0 

16 116 125 0 0 

Average 112 155 0.33 0.19 

Table 2c. Test Results: “New” Plot Averages 

Plot Number 

(N) 

Green PP > 5” 

d.b.h. 

Total Trees 

per Acre 

2003 

Attacks 

% 2003 

Attacks 

3 162 218 0 0 

6 119 221 4 3.36 

9 169 191 3 1.78 

11 118 168 5 4.23 

14 102 122 0 0 

17 105 124 4 3.80 

Average 129 174 2.67 2.19