1 

 Report Number R4-02-01 

 October, 2001 

2000-2001 REDFISH LAKE VERBENONE TRIAL 

Progress Report 

R.A. Progar 

Forest Health protection 

Boise, Idaho 

Populations of mountain pine beetle (MPB) Dendroctonus ponderosae Hopkins have 

been building at the Sawtooth National Recreation Area (SNRA) in south-central Idaho. 

Tree losses associated with outbreaks of MPB have been described as devastating 

(Safranyik 1988), with changes in density, stand age and species composition occurring 

within several years. Outbreaks of MPB are usually targeted toward the oldest and 

largest trees (> 8 inches in diameter) in a stand. Mass attack by many beetles on 

individual trees in a brief period (over 1 or 2 days) overwhelm tree defenses causing 

imminent mortality (Amman and Cole 1983). Emergence commonly occurs over a 2-3 

week period (Amman and Cole 1983). Evidence of beetle infestation usually consists of 

pitch tubes where beetles have entered the tree and boring dust in bark crevasses and 

at the base of the tree (Amman and Cole 1983). 

Lodgepole pine (Pinus contorta) is the dominant tree species at the Redfish Lake 

Recreation Complex. A significant percent of the lodgepole pines are over 8 inches in 

dbh (diameter breast height) and at risk of being attacked and killed by MPB. 

Lodgepole pine mortality at Redfish Lake has currently increased to levels that diminish 

the ambiance and esthetic integrity of the recreational complex. To protect trees that 

enhance the recreational value of the campgrounds, picnic areas, lodge and visitor 

center the insecticide carbaryl has been applied to the tree bole, deterring successful 

beetle attack. Trees immediately adjacent to the lake cannot be chemically treated 

because of the unacceptable risk of water contamination resulting from over-spray. To 

attempt to deter beetle attacks within this sensitive area an experimental 

antiaggregative compound (verbenone) was placed among lakeside trees in 2000 and 

in 2001. 

Verbenone (4,6,6-trimethylbicyclo[3.1.1]-hept-3-en-2-one) is considered the principal 

antiaggregative pheromone component of MPB. Verbenone has not been registered for 

operational use on MPB by the U.S. Environmental Protection Agency (EPA), however 

the material may be used for experimental purposes on a total of less than 250 acres 

nationwide per year (59 FR 3681). Much of the literature has shown that verbenone 

reduces the incidence of successful MPB attacks on lodgepole pine (Miller et al. 1995, 

Amman and Ryan 1994, Amman et al. 1991, Shea et al. 1991, Amman et al. 1989, 

Lindgren et al. 1989, Schmitz 1988), other authors have found either inconsistent 

results on lodgepole (Gibson et al. 1991) or that verbenone was ineffective in preventing 

MPB attacks on ponderosa pine (Bentz et al, 1989, Lister et al. 1990). However, since 

there is no alternative method to deter beetle attacks on waterside trees at the SNRA, 
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we initiated a trial to assess and demonstrate the efficacy of verbenone in preventing 

MPB attack. This trial was initiated using a higher concentration (5g pouches) with an 

increased rate of release (25-35 mg per day) over previous trials. The objective of this 

evaluation is to demonstrate the ability of verbenone to provide protection against beetle 

attack in environmentally sensitive areas through the course of a multi-year outbreak. 

This investigation is of particular interest because there has been no prior study 

evaluating the efficacy of verbenone for more than a single year. The ability of the 

compound to preserve stand integrity throughout the course of a multi-year outbreak 

would be a substantial addition to MPB management techniques. 

Methods 

On June 8, 2000, sixteen one-half acre plots were located in campgrounds and outside 

visitor facilities in lodgepole stands along the shoreline of Little Redfish and Redfish 

lakes. The species, dbh (diameter breast height), year of attack (old MPB attack prior to 

1999 vs. new attack in 1999 containing brood) were measured and tabulated for each 

tree on the plots. Plots were randomized and eight were selected for treatment with 

verbenone pouches. The eight remaining untreated plots were used as comparison 

plots. On July 5, 2000 and on June 14, 2001, twenty pouches were placed on the north 

facing side of the tree 12 ft. above the ground at a spacing of one pouch per 1000 sq ft. 

in each treated plot. We also erected attractant-pheromone baited funnel traps at three 

locations within the Stanley Basin to monitor beetle emergence. The plots were 

revisited in October 2000 and September 2001 when current-year beetle attacks were 

tabulated for evaluation. 
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Results and Discussion 

Analysis of host tree dbh showed no significant difference within size class among plots 

receiving verbenone and those in the untreated check (Fig. 1). 

In 2000, treatment comparison of MPB attacks by ANOVA indicated significantly (P 

0.05) more lodgepole pines were attacked on the untreated plots than on plots 

containing the verbenone pouches (F = 6.9; df = 1, 14;P = 0.02). The mean number of 

successfully attacked lodgepole pine per plot was 16.5 (SE=5.28) for untreated plots 

and 2.37 (SE=1.03) in plots containing verbenone pouches Fig. 2). In 2001, beetle 

attacks increased by 35% to an average of 23 trees per untreated plot and by 133% to 

an average of 7 attacked trees in the verbenone treated plots. The increase in the 

incidence of successful attack on treated plots may indicate a threshold intensity of 

beetle pressure for verbenone. Although more trees were attacked by MPB in 

verbenone treated plots in 2001 than in 2000, there were significantly (F = 13.1; df = 1, 

14;P = 0.003) fewer successful attacks in the plots containing verbenone than in 

untreated plots (Fig. 2). 

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5-7" 7.1-9" 9.1-11" 11.1-13" 13.1-15"

DBH

Average number of trees per 1/2 acre plot

Untreated

Verbenone

Figure 1. Average per plot density of susceptible lodgepole pine between treatments by dbh. 
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Figure 2. Average number of successful MPB attacks per plot during 2000 and 2001. 

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2000 2001

Year

Average number of MPB attacks per 1/2 cacre plot

Untreated

Verbenone

Examination of treatment differences within size class (Figs. 3 & 4) showed 

significantly (P  JUHDWHU QXPEHUV RI DWWDFNV LQ WKH XQWUHDWHG FKHFN RQ

smaller size class trees (<11” dbh) during both years. However, in either 2000 or 

2001, trees greater than 11” dbh did not show significant differences in the 

number of MPB attacks between treatments. In 2000, an average of 3.5 (SE = 

1.4) trees greater than 11” dbh were successfully attacked on the untreated plots 

whereas 0.87 (SE = 0.4) were attacked on plots containing verbenone pouches 

(Trees < 11”: dbh: F = 8.05; df = 1, 14; P = 0.01; Trees > 11”: F = 3.09; df = 1, 14; 

P = 0.10)). In 2001, there was an average of 4 trees (SE = 1.8) (>11” dbh) per 

plot successfully attacked on the untreated plots and 3.87 (SE = 1.6) trees on the 

verbenone treated plots (Trees < 11”dbh: F = 25.63; df = 1, 14; P = 0.0002; 

Trees > 11” dbh: = .F = 0.002; df = 1, 14; P = 0.95). Lack of significant 

differences between treatments among trees with greater dbh may indicated that 

verbenone may lose it effectiveness on larger trees under conditions of 

increasing beetle pressure. Future studies should include a sufficient number of 

trees with a dbh greater than 11” to adequately evaluate the relationship of 
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verbenone and MPB in larger size-classed trees. 

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5-7"" 7.1-9" 9.1-11" 11.1-13" 13.1-15" >15" DBH

Average number of MPB attacks per 1/2 acre plot

2000 Untreated

2000 Verbenone

2001 Untreated

2001 Verbenone

Figure 3. Comparison of trees by dbh size class between untreated plots and plots treated with 

verbenone during 2000 and 2001. 

Verbenone showed no selective ability in protecting individual trees. Trees containing 

treatment pouches within the verbenone plots exhibited the same evidence of beetle 

attack as trees that did not contain pouches although significantly fewer attacks 

occurred on verbenone treated plots. 

In 2000 and 2001, there were no significant differences (yr. 2000 - F = 1; df = 1,14; P = 

0.33; yr. 2001 – F = 0.07; df = 1, 14; P = 0.788) between treatments in the number of 

trees that pitched-out beetles. There were significantly higher numbers of strip attacks 

in the untreated plots in 2000 (0 = 5.62) than in the plots containing verbenone (0 = 1) (F 

= 5.81; df = 1, 14; P = 0.03). Also in 2001, there were higher numbers of strip attacks in 

the untreated plots (0 = 3.75) than in the verbenone treated plots (0 = 2.37), however 

the difference was not significant (F = 2.55; df = 1, 14; P = 0.13). 
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2 1

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4 4

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0

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25

2000 <11" dbh 2000 > 11" dbh 2001 < 11" dbh 2001 > 11" dbh

Year and tree size

Average number of MPB attacks per 1/2 acre 

plot 

Untreated

Verbenone

Figure 4. Comparison of MPB attacks on lodgepole pine with a dbh less than and greater than 11”. 

Mountain pine beetle populations are continuing to build at the Redfish Lake 

Recreational Complex (Their, 3420 letter, dated February 6, 2001 to Forest Supervisor 

Sawtooth NF). In 2002-2004 we plan to continue the current study to assess the ability 

of verbenone to deter MPB attack of susceptible lodgepole pine stands under increasing 

MPB pressures. As the outbreak expands through the recreational area, fewer 

unattacked trees will be available increasing pressure on unattacked trees. Future trials 

will assess the long-term ability of verbenone to deter beetle attack under conditions of 

increasing beetle severity. 
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Literature Cited 

Amman, G.W. and W.E. Cole. 1983. Mountain pine beetle dynamics in lodgepole pine 

forests part II: Population dynamics. Intermountain Forest and Range Experimental 

Station General Technical Report INT-145. 59 pp. 

Amman, G.D. and K.C. Ryan. 1994. Using pheromone to protect heat-injured lodgepole 

pine from mountain pine beetle infestation. Intermountain Research station Research 

Note INT-419. 7 pp. 

Amman, G.D., R.W. Their, J.C. Weatherby, L.A. Rasmussen, and S.A. Munson. 1991. 

Optimum dosage of verbenone to reduce infestation of mountain pine beetle in 

lodgepole pine stands of central Idaho. Intermountain Research Station Research 

Paper INT-446. 5 pp. 

Amman, G.D., R.W. Their, M.D. McGregor, and R.F. Schmitz. 1989. Efficacy of 

verbenone in reducing lodgepole pine infestation by mountain pine beetles in Idaho. 

Can. J. For. Res. 19: 60-64. 

Bentz, B.,C.K. Lister, J.M. Schmid, S.A. Mata, L.A. Rasmussen, and D. Haneman. 

1989. Does verbenone reduce mountain pine beetle attacks in susceptible stands of 

ponderosa pine? USDA Research Note RM-495. 4 pp. 

Lindgren, B.S., J.H. Borden, G.H. Cushon, L.J. Chong, and C.J. Higgins. 1989. 

Reduction of mountain pine beetle (Coleoptera: Scolytidae) attacks by verbenone in 

lodgepole pine stands in British Columbia. Can. J. For. Res. 19: 65-68. 

Lister, C.K., J.M. Schmid, S.A. Mata, D. Haneman, C. O’Neil, J. Pasek, and L. Sower. 

1990. Verbenone bubble caps ineffective as a preventive strategy against mountain 

pine beetle attacks in ponderosa pine. USDA Research NoteRM-501. 3 pp. 

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. 

Intermountain Research Station Research Paper INT-444. 

Miller, D.R., J.H. Borden, and B.S. Lindgren. 1995. Verbenone: Dose-dependent 

interruption of pheromone-based attraction of three sympatric species of pine bark 

beetles (Coleoptera: Scolytidae). Environmental Entomology 24: 692-696. 

Rasmussen, L.A. 1974. Flight and attack behavior of mountain pine beetles in lodgepole 

pine of northern Utah and southern Idaho. Intermountain Forest and Range Experiment 

Station Research Note INT-180. 7pp. 

Safranyik, L. 1988. Mountain pine beetle: Biology overview. In : Amman, G.D. (ed.) 

Proceedings- Symposium on the management of lodgepole pine to minimize the losses 

to the mountain pine beetle. Kalispell, MT, July 12-14 1988. pp. 9-13. 
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Schmitz, R.F. 1988. Efficacy of verbenone for preventing infestation of high-value 

lodgepole pine stands by the mountain pine beetle. In : Amman, G.D. (ed.) 

Proceedings- Symposium on the management of lodgepole pine to minimize the losses 

to the mountain pine beetle. Kalispell, MT, July 12-14 1988. pp. 75-79 

Shea, P.J., M.D. McGregor, and G.E. Daterman. 1992. Aerial application of verbenone 

reduces attack of lodgepole pine by mountain pine beetle. Can. J. For. Res. 22:436-

441. 

Their, R.W. 2001. File code 3420, February 8, 2001. Letter to the Forest Supervisor, 

Sawtooth. NF. 

59 FR 3681; July 7, 1994. Arthropod Pheromones; Experimental Use Permits