United States 

Department of 

Agriculture

Forest 

Service 

Intermountain 

Region 

Forest Health Protection 

Boise Field Office 

1249 South Vinnell Way, Suite 200 

Boise, ID 83709-1663

 Caring for the Land and Serving People Printed on Recycled Paper 

File Code: 3420 Date: October 9, 2003 

Route To: 

Subject: Verbenone in Administrative Areas, Sawtooth National Recreation Area, Redfish 

Lakes 

To: Forest Supervisor, Sawtooth NF 

 

 

At the request of SNRA personnel, Boise Field Office Forest Health Protection (FHP) personnel 

have been applying the mountain pine beetle antiaggregant verbenone to lodgepole trees among 

campgrounds and administrative areas around Little Redfish and Redfish Lakes from 2000-2003. 

The enclosed report (BFO-PR-04-02) summarizes the results of the verbenone trial over the past 

4 years. 

Please contact Rob Progar or Dayle Bennett if you need additional information or assistance. 

/s/ Dayle D. Bennett (for) 

WILLIAM W. BOETTCHER 

Director, State and Private Forestry 

 

Enclosure 

RProgar:al 
2

2000-2003 REDFISH LAKE VERBENONE TRIAL 

Progress Report, October 2003 

BFO-PR-04-02 

R.A. Progar, Forest Health Protection, USDA Forest Service, Boise Field Office, 1249 

South Vinnell Way, Suite 200, Boise, Idaho 83709 

Abstract

Mountain pine beetle, Dendroctonus ponderosae is the most common cause of mortality 

of mature lodgepole pine (Pinus contorta var. latifolia). In 2000-2003, the 

antiaggregative compound verbenone was applied annually to the same lodgepole pine 

stands in campgrounds and resort facilities at the Sawtooth National Recreation Area 

(SNRA) in central Idaho to assess its ability in deterring mountain pine beetle attack 

through the course of a multi-year outbreak. Verbenone was applied at the rate of 40 

5g pouches/acre releasing 25-35 mg/24h at 20°C. Significantly fewer trees were 

attacked and killed in the verbenone plots during 2000 and 2001. However, of the plots 

containing verbenone, a higher percentage of large trees were attacked in the second 

year of treatment, suggesting the efficacy of verbenone may diminish under increasing 

beetle pressure. In 2002 and 2003, there were nearly twice as many trees attacked and 

killed in the verbenone plots as in the untreated plots. It is hypothesized that the 

change in the performance of verbenone may be due to the large beetle population 

overwhelming the treatment. 

Introduction 

The mountain pine beetle (MPB), Dendroctonus ponderosae is considered the primary 

cause of mortality of mature lodgepole pine (Pinus contorta var latifolia (Cole et al. 

1985). Tree losses associated with outbreaks of MPB have been described as 

devastating (Safranyik 1988), exceeding a million trees a year in some forests (Klein et 

al. 1978), causing changes in density, stand age, and species composition. MPB also 

causes serious mortality in ponderosa pine (Pinus. ponderosa), western white pine (P. 

monticola ), and whitebark pine (P. albicaulis) (Amman and Cole 1983). Trees from 4-5 

inches in diameter at breast height (d.b.h.) and greater are susceptible to attack by 

mountain pine beetle (Furniss and Carolin 1977). 

TheSNRA is the most popular recreation area in central Idaho. The region contains the 

headwaters of the Salmon River, over 300 lakes, and is characterized by a high 

elevation (> 6,000 feet) alpine climate. One of the prime attractions of the area is the 

Redfish Lake Recreation complex with its campgrounds, lodge, and resort facilities. 
3

Lodgepole pine is the dominant tree species in the SNRA. A significant percent of the 

pine is mature (> 8 inches d.b.h.) and at risk of beetle attack. Over the past several 

years, the building MPB population has caused tree mortality that severely impact the 

ambiance and esthetic integrity of the recreation area. 

Current practices to lessen the severity of an MPB epidemic on lodgepole pine rely 

heavily on stand manipulation (Amman and Baker 1972, Amman et al. 1991), the use of 

attractive pheromones, or the application of prophylactic chemical insecticides. The 

insecticide carbaryl has been applied to campground trees to protect them from beetle 

attack (Gibson 1982). However, trees immediately adjacent to natural bodies of water 

cannot be chemically treated because of the unacceptable risk of aquatic contamination 

resulting from spray drift or leaching. To attempt to deter beetle attacks within this 

sensitive area, the experimental antiaggregative compound verbenone was placed 

among lakeside trees in 2000-2003. 

Verbenone is the principal antiaggregative pheromone component of MPB and was first 

isolated and identified by Pittman et al. (1969). The semiochemical has been shown to 

reduce the incidence of successful MPB attacks on lodgepole pine (Schmitz 1988, 

Lindgren et al. 1989, Amman et al. 1991, Shea et al. 1992, Amman and Ryan 1994, 

Miller et al. 1995). Other authors did not find significant differences between verbenone 

and untreated plots (Amman et al. 1989) or reported encouraging early results but later 

experiments yielded ambiguous data (Amman and Lindgren 1995). Verbenone is 

effective in suppressing the aggregation of male and female southern pine beetles 

(SPB) (Dendroctonus frontalis) (Billings et al. 1995) and was registered for SPB 

suppression in 1999. This study was initiated to assess the efficacy of verbenone in 

deterring MPB attack in high value trees in campgrounds in sensitive riparian habitats 

through the course of a multi-year outbreak. 

Another semiochemical is the antiaggregant pheromone MCH (3-methyl-2-cyclohexen1-one) and has been shown to reduce attacks by over 90 percent on Douglas-fir 

(Pseudotsuga menziesii) by the Douglas-fir beetle (Dendroctonus pseudotsugae). MCH 

was registered in 1999 and is being used to operationally suppress this important pest. 

Trials of MCH have also been conducted to suppress spruce beetle (Dendroctonus 

rufipennis). However, results have been inconsistent and inconclusive. An excellent 

review of the literature on MCH can be found in Zogas et al. (2001). 

Methods 

In June 2000, 16 one-half acre rectangular (210 x 105 ft) plots were located in and 

around campgrounds and adjacent visitor facilities (44°09’ N 114°54’ W) in mature 

lodgepole pine stands along the shoreline of Little Redfish and Redfish lakes in the 

SNRA. The species and d.b.h. were recorded for each plot tree. In 2002, several of the 

plots were compromised by management activities and were dropped from the study. 
4

The pheromone formulation consisted of 98 percent technical grade, 80 percent (-), 20 

percent (+) verbenone (4,6,6-trimethylbicyclo[3.1.1]-hept-3-en-2-one). The verbenone 

was formulated by and purchased from Phero Tech, Inc., Delta, British Columbia, 

Canada, and applied at the rate of 40 5g pouches/ac. This study used more verbenone 

(5g pouches) with a higher rate of release (25-35 mg/day at 20°C) over prior studies of 

verbenone on MPB. On July 5, 2000, June 14, 2001, June 12, 2002, and June 17, 

2003, verbenone pouches were placed on the north-facing side of the same 20 trees in 

each of eight randomly selected plots at a height of 12 feet and a spacing of one pouch 

every 32 feet or one pouch/1000 feet. The eight remaining untreated plots were used 

for comparison. Since the effective duration of elution from the verbenone pouch was 

considered to be 140-200 days at 20°C, the entire span of time over which MPB 

emerged and took flight should be encompassed. At the SNRA, the majority of MPB 

beetle flight is usually concentrated in a 2-week period during July. However, sufficient 

numbers emerge from June through September to warrant extended coverage. During 

October 2000, September 2001, October 2002, and September 2003, current-year 

beetle attacks were recorded and evaluated. One-way ANOVA (Sokal and Rohlf 1981) 

was used to compare the impacts of MPB on lodgepole pine between treatments. 

Treatments were considered significant at P ≤ 0.05. SAS JMP software (SAS 2001) 

was used for all analyses by ANOVA. 

Results and Discussion 

Pretreatment analysis of host tree dbh showed no significant difference in the numbers 

of trees within size class between plots receiving verbenone and those in the untreated 

check (Figure 1). 

65

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0

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70

80

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

DBH Class

Avg. no. trees/0.5 ac

Untreated

Verbenone

Figure 1. Average per plot density of susceptible lodgepole pine between treatments by d.b.h.
5

In 2000, treatment comparison of MPB attacks indicated significantly 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 (Figure 2). 

17

23

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7 7

29

0

5

10

15

20

25

30

35

2000 2001 2002 2003

Year

Avg. no. MPB attacks/0.5 ac

Untreated

Verbenone

Figure 2. Average number of successful MPB attacks/plot during 2000-2003. 

In 2001, the number of beetle killed trees increased by 39 percent to an average of 23 

trees (SE = 3.64) per untreated plot and by nearly 200 percent to an average of seven 

trees (SE = 2.80) killed by beetles in the verbenone-treated plots. The increase in the 

incidence of successful attack on trees in treated plots may indicate a threshold level of 

beetle abundance in response to verbenone. Although more trees were killed by MPB 

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

df = 1, 14; P = 0.003) beetle killed trees in the plots containing verbenone than in 

untreated plots (Figure 2). In 2002, there were an average of 29 MPB killed trees (SE = 

9.21) in the verbenone plots and 16 killed trees (SE = 4.99) in the untreated plots. 

However, differences in the number of MPB killed trees between the treatments were 

not significant (F = 1.61; df = 1, 12; P = 0.229). This event was surprising because of 

the successful performance of verbenone in deterring MPB attack over the past 2 years. 

In 2003, there were more than twice as many trees killed by MPB in the verbenone 

(mean = 7.42, SE = 2.22) treated plots than in the untreated plots (mean = 3.14, SE = 

1.29), however the difference was not significant (P = 0.12). 
6

Several hypotheses have evolved to describe the year-to-year inconsistency of the 

performance of verbenone in suppressing MPB attacks on lodgepole pine: (1) the 

population of beetles becomes so large that they overwhelm the verbenone signal; (2) 

MPB undergoes a physiological change that alters their response to verbenone; and (3) 

the verbenone eluted from the pouches before beetle emergence and flight had ended. 

The urgency of the beetles to find suitable host trees may overwhelm the verbenone 

signal. Because attacks occur simultaneously on many trees, the likelihood of beetles 

landing on trees that have been previously attacked (or trees with verbenone) increases 

and leads to a higher probability of successful attacks (Amman and Lindgren 1995). 

A similar response was encountered in trials of verbenone in central Idaho in the early 

1990’s (Amman et al. 1991); several years of satisfactory results were followed by a 

poor response to the antiaggregant. Results by Rasmussen (Amman and Lindgren 

1995) suggest that since the large suitable host trees are killed by MPB attack in 

previous years, only small diameter host trees are available in the current year. In the 

small trees larval survival is lower (Cole et al. 1976), and adult beetles take longer to 

develop and are smaller in size (Amman and Cole 1983). Amman and Lindgren (1995) 

note that beetles developing from the thin phloem of small diameter trees tend to ignore 

the verbenone signal. Hence, as the population of host trees decrease to a diameter 

where beetle survival becomes marginal, the surviving beetles may either not respond 

to the verbenone signal or respond in a different manner. As a result of the shift in 

beetle response, trees in the plots containing verbenone may become susceptible to 

MPB attack and be killed. 

There is the possibility the verbenone may have eluted from the pouches before beetle 

emergence and flight ended for the year. The span of time that MPB emerged at the 

SNRA varies with trap location and between years. In 2000, the span of emergence as 

measured by Lindgren funnel traps occurred from early July through late August and 

peaked on July 18 (B. Bentz unpublished data). In 2001, the period of emergence 

spanned from early July through mid-September with peaks occurring in mid-July and 

late August to early September (B. Bentz unpublished data, S. Munson, S. Seybold, and 

D. Ross unpublished data). In 2002, MPB emergence at Redfish Lake peaked during 

the third week of July (B. Bentz unpublished data). Although the rate of elution is 

defined as 25mg/day at 20°C on the product label, the rate can vary with weather and 

temperature. For SPB, the expected lifespan of a verbenone pouch is 25-40 days in the 

southern United States (Phero Tech Product # RD-0372/000 label). In the high 

elevations of central Idaho where the high temperature averages in the upper 70’s 

during July-August and the low temperature averages in the upper 30’s for the same 

period, the elution of verbenone was expected to include the entire MPB flight. 
7

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2000 < 11 2000 > 11 2001<11 2001 > 11 2002 < 11 2002 > 11 2003 < 11 2003 > 11

Year and dbh less than and greater than 11 in. 

Avg. no. MPB attacks/0.5 ac

Untreated

Verbenone

Figure 3. Comparison of MPB attacks over the duration of the outbreak by small and large d.b.h. 

Examination of treatment differences by tree d.b.h. (Figures 3 and 4) showed 

significantly greater numbers of beetle-killed trees < 11 inches d.b.h. in untreated plots 

than in verbenone-treated plots during 2000 and 2001. However, in each of these 

years, there was no significant difference in the number of successful beetle attacks on 

trees > 11 inches d.b.h. between verbenone-treated and untreated plots. In 2000, an 

average of 3.5 (SE = 1.4) trees > 11 inches d.b.h. were successfully attacked and killed 

on the untreated plots whereas 0.87 (SE = 0.4) were killed on plots containing 

verbenone pouches (trees < 11 inches: d.b.h.: F = 8.05; df = 1, 14; P = 0.01; trees > 11 

inches: F = 3.09; df = 1, 14; P = 0.10). In 2001, there was an average of four trees (SE 

= 1.8) > 11 inches d.b.h. that were successfully attacked on the untreated plots and 

3.87 (SE = 1.6) trees on the verbenone-treated plots (trees < 11 inches d.b.h.: F = 

25.63; df = 1, 14; P = 0.0002; trees > 11 inches d.b.h.: F = 0.002; df = 1, 14; P = 0.95). 

Lack of significant differences during 2000-2001 between treatments among trees > 11 

inches d.b.h. may indicate a decreasing efficacy of verbenone on larger trees under 

conditions of increasing beetle pressure or may be attributed to the small plot size used 

in this study. 
8

Average number of trees remaining after four years of verbenone treatment

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

Size Class

Average # trees remaining per plot

Average total untreated

Average remaining untreated

Average total verbenone

Average remaining verbenone

Figure 4. Average number of trees remaining by d.b.h. size class after 4 years by treatment and d.b.h.

In 2002, the differences in the number of trees attacked and killed by MPB between 

treatments approached significance with an average of 7.3 (SE = 2.5) trees > 11 inches 

d.b.h. attacked and killed on plots containing verbenone and 2.0 (SE = 0.9) trees > 11 

inches d.b.h. on the untreated plots (trees > 11 inches d.b.h.: F = 3.86; df = 1, 12; P = 

0.07). Figure 4 shows that after 3 years, few trees > 11 inches d.b.h. remain on either 

the untreated plots or the plots containing verbenone. There was an average of 22 

MPB killed trees < 11 inches d.b.h. on the verbenone treated plots and 14 trees killed 

on the untreated plots (trees < 11 inches d.b.h.: F = 0.9; df = 1, 12; P = 0.36). After 

the2003 MPB attacks, there are no trees greater than 11 inches d.b.h. remaining on the 

plots. Approximately one-third of the trees in the 9-11-inch size class remain in the 

verbenone treated plots and average of a single tree in this size class remains on the 

untreated plots. 

Shea (1992) noted there were high numbers of unsuccessfully attacked trees 

(pitchouts) in plots treated with verbenone when compared with untreated plots. There 

were no significant differences in the number of pitchouts between treatments during 

2000 and 2001 (yr 2000: F = 1.03; df = 1, 14; P = 0.33; yr 2001: F = 0.07; df = 1, 14; P 

= 0.788). However, in 2002, there were nearly twice as many pitchouts in the 

verbenone treated plots (0 = 8.28, SE = 1.61) than in the untreated plots (0 = 4.42, SE = 

0.84) (F = 4.49; df = 1, 12; P = 0.05). This response may be related to plot size and to 

beetle density and become more pronounced with larger study plots and increasing 

beetle abundance. In 2003, there were more pitchouts in the verbenone treated plots 

(8.3 vs. 5.3) but the difference was not significant. 
9

There were significantly higher numbers of strip attacks among untreated plots in 2000 

(0 = 5.62, SE = 5.15) than in the plots containing verbenone (0 = 1, SE = 0.59) (F = 

5.81; df = 1, 14; P = 0.03). The number of strip attacks in untreated (0 = 3.75, SE = 

0.61) vs. verbenone (0 = 2.37, SE = 0.59) plots was not significantly different in 2001 (F 

= 2.55; df = 1, 14; P = 0.13). In 2002, there were more strip attacks occurring in the 

verbenone plots (0 = 14.14, SE = 3.39) than in the untreated plots (0 = 10.71, SE = 

5.12), however, the difference was not significant (F = 0.77; df = 1, 12; P = 0.39). In 

2003, there were significantly (F = 2.93; df = 1, 12; P = 0.03) more strip attacks in the 

verbenone treated plots (0 = 7, SE =1.97) than the untreated plots (0 = 1.85, SE = 0.67). 

Individual trees containing pouches within the verbenone plots showed the same 

evidence of beetle attack as trees that did not contain pouches, although in general, 

significantly fewer attacks occurred on verbenone-treated plots. There was no 

observable effect of individual tree protection conferred by the verbenone pouch on a 

tree. However, there was only a single verbenone pouch placed on each treated tree, 

and recommendations for SPB include up to nine verbenone pouches per tree for 

exclusion (Phero Tech Product # RD-0372/000 label). This area of research needs to 

be explored for mountain pine beetle to determine if there may be a dose response for 

individual trees. 

Mountain pine beetle populations continue to build at the Redfish Lake Recreational 

Complex (Thier, 3420 letter, dated February 6, 2001 to Forest Supervisor Sawtooth 

NF.). In 2003-2004, we plan to continue the current study to assess the ability of 

verbenone to deter MPB attack on the same susceptible lodgepole pine stands for the 

duration of an outbreak. As the beetle outbreak expands throughout the SNRA area, 

fewer unattacked trees will be available, thus increasing pressure on trees within the 

verbenone plots. Future studies should include a sufficient number of trees with a d.b.h. 

> 11 inches d.b.h. to adequately evaluate the relationship of verbenone and MPB in 

larger size-classed trees. Also, the relationship between verbenone and beetle density 

needs to be resolved before verbenone can be considered an operational tool for 

protection from attack by MPB.
10

Literature Cited 

Amman, G.D., and B.H. Baker. 1972. Mountain pine beetle influence on lodgepole 

stand and structure. J. For. 7: 204-205. 

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

forests part II: Population dynamics. USDA For. Serv. Gen. Tech. Rep. INT-145. 59 

p. 

Amman, G.D., R.W. Thier, 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. 

Amman, G.D., R.W. Thier, 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. USDA For. Serv. Res. Pap. INT-446. 5 p. 

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

lodgepole pine from mountain pine beetle infestation. USDA For. Serv. Res. Note 

INT-419. 7 p. 

Amman, G.D. and B.S. Lindgren. 1995. Semiochemicals for management of mountain 

pine beetle: Status of research and application. USDA For. Serv. Gen. Tech. Rep. 

INT-GTR-318.22 p. 

Billings, R. F., C. W. Berisford, S. M. Salom, and T. L. Payne. 1995. Applications of 

semiochemicals in the management of southern pine beetle infestations: current 

status of research, P. 30-38. in Application of semiochemicals for management of 

bark beetle infestations: proceedings of an informal conference. Salom, S. M. and K. 

R. Hobson (eds.) USDA For. Serv. Gen. Tech. Rept. INT-GTR-318. 

Cole, W.E., G.D. Amman, and C.E. Jensen. 1985. Mountain pine beetle dynamics in 

lodgepole pine forests. Part III: Sampling and modeling of mountain pine beetle 

populations. USDA For. Serv. Gen. Tech. Rep. INT-188. 46 p. 

Cole, W.E. G.D. Amman, and C.E. Jensen. 1976. Mathematical models for the 

mountain pine beetle-lodgepole pine interaction. Env. Ent. 5: 11-19. 

Furniss, R.L., and V.M. Carolinches 1977. Western Forest Insects. USDA For. Serv. 

Misc. Pub. No 1339. Washington, D.C. 654 p. 

Gibson, K.E. 1982. Management alternatives for lodgepole pine recreational facilities 

threatened by the mountain pine beetle. USDA For. Serv. Pest Manage. Rept. 82-

27, Nov. 1982, Missoula, MT. 3 p. 
11

Klein, W.H., D.L. Parker, and C.E. Jensen. 1978. Attack, emergence and stand 

depletion trends of mountain pine beetle in a lodgepole pine stand during an 

outbreak. Environ. Entomol. 7: 732-737. 

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. 

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). Environ. Entomol. 24: 692-696. 

Phero Tech Inc. 2000. Verbenone pouch. Phero Tech product # RD-0372/000 label, 

Phero Tech Inc., Delta, BC. 

Pittman, G.D., J.P. Vite, G.W. Kinzer, and A.F. Fentiman. 1969. Specificity of 

population-aggregation pheromones in Dendroctonus. J. Insect Physiol. 15: 363-

366. 

Safranyik, L. 1988. Mountain pine beetle: Biology overview. P. 9-13 in Proc. 

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

mountain pine beetle, Amman, G.D. (ed.). USDA For. Serv. Gen. Tech. Rept. INT262. 

SAS Institute, Inc. 2001. JMP Statistics and Graphics Guide. - SAS Institute, Inc., Cary, 

NC. 634 p. 

Schmitz, R.F. 1988. Efficacy of verbenone for preventing infestation of high-value 

lodgepole pine stands by the mountain pine beetle. P. 75-79 in Proc. Symposium on 

the management of lodgepole pine to minimize the losses to the mountain pine 

beetle, Amman, G.D. (ed.). USDA For. Serv. Gen. Tech. Rept. INT-262. 

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. 

Sokal, R. R., and F. J. Rolf. 1981. Biometry. W. H. Freeman and Company, New York. 

859 p. 

Zogas, K., E. Holsten, J. Boughton, and P. W. Forward. 2001. Summary of thirty years 

of field testing of MCH: Antiaggregation pheromone of the spruce bark beetle and 

the Douglas-fir beetle. USDA For. Serv. Tech. Rept. R10-TP-91. 26 p.