United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

Research Paper

PNW-RP-544

March 2002

Release Rates of Methylcyclohexenone

and Verbenone from Bubble Cap and

Bead Releasers Under Field Conditions

Suitable for the Management of Bark

Beetles in California, Oregon, and Alaska

Edward H. Holsten, Warren Webb, Patrick J. Shea, and

Richard A. Werner
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 or 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.

Edward H. Holsten is a research entomologist, U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station, 3301 C Street, Suite 522, Anchorage, AK

99503; Warren Webb was an associate professor (retired), Forest Science Department, Oregon State University, Corvallis, OR 97331-7501; Patrick J. Shea was a research entomologist (retired), U.S. Department of Agriculture, Forest Service, Pacific

Southwest Research Station, Davis, CA 95616; and Richard A. Werner was a research entomologist (retired), U.S. Department of Agriculture, Forest Service, Pacific

Northwest Research Station, Institute of Northern Forestry, Fairbanks, AK 99775-5500

(now closed).

Authors

Errata

for PNW-RP-544

1. Equation 2 on page 3 is changed to the following: dy/dX=b + 2cX

2. Text on page 6, paragraph 1, second to last sentence, should read:

 The slopes, however, were not significantly different between the four sites.
Holsten, Edward H.; Webb, Warren; Shea, Patrick J.; Werner, Richard A. 2002.

Release rates of methylcyclohexenone and verbenone from bubble cap and bead

releasers under field conditions suitable for the management of bark beetles in

California, Oregon, and Alaska. Res. Pap. PNW-RP-544. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 21 p.

Devices releasing antiaggregation pheromones, such as MCH (3-methyl-2-cyclohexen1-one) and verbenone (4-methylene-6,6-dimethylbicyclo(3.1.1)hept-2-ene), are used

experimentally to manipulate destructive populations of bark beetles. Two slow release

devices, bubble caps attached to boles of trees and granular beads placed on the

ground, were tested in forests of California, Oregon, and Alaska to determine their

release rates. The hypothesis was that ambient air and soil temperatures were major

determinants in the release rates of the releaser devices. Release rates of both bubble

caps and beads differed greatly. The fastest rate was for bubble caps at a warm, California pine (Pinus spp.) site where it was 15 times faster than the rate at a cool Sitka

spruce (Picea sitchensis Bong. Carr.) site in Alaska. Beads released MCH quickly and

were rendered ineffective in less than 2 weeks. Little or no release occurred thereafter,

regardless of the amount of pheromone remaining in the bead, or litter layer temperature. Release rates determined under field conditions are useful for the field entomologist and are vital to the development of models for semiochemical dispersion.

Keywords: Semiochemicals, release rates, antiaggregation pheromones, bark beetles,

temperature, MCH, verbenone.

The data reported here are from studies on the release rates of MCH and verbenone

from two commonly used release devices, bubble caps and beads. These studies were

carried out in California, Oregon, and Alaska. Release rates of both bubble caps and

beads varied greatly. Ambient air and litter layer temperatures were the major determinants in release rates of the releaser devices. The fastest release rates from bubble

caps occurred at a warm California pine site and were 15 times the rate from a cool

spruce site in Alaska. Bead releasers quickly released semiochemicals for about 2

weeks. Little or no release occurred thereafter, regardless of the amount of pheromone

remaining in the bead, or litter layer temperature.

1 Introduction

1 Materials and Methods

1 Study Area Characteristics

2 Experimental Design

2 Quantification of Release Rate

3 Temperature

3 Results and Discussion

3 Release from Bubble Caps

11 Release from Beads

17 Conclusions

17 Acknowledgments

18 English Equivalents

18 Literature Cited

Abstract

Summary

Contents
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1

In the past few decades, outbreaks of various types of bark beetles in western North

America, including Alaska, have brought about renewed interest in these devastating

forest pests. Spruce beetle (Dendroctonus rufipennis (Kirby)) infestations impacted

more than 1 000 000 ha of forested land in south-central Alaska in the last decade

(Matthews and others 1997). Many of these infested stands have over 90 percent tree

mortality. The impact of these outbreaks and the anticipated impact of future outbreaks

have stimulated the continuation of basic and applied research on the use of semiochemicals to manipulate populations of bark beetles (Holsten 1994, Shea 1995, Werner

1994, Werner and Holsten 1995).

Bark beetle semiochemical communication systems are complex, involving insect

physiology, pheromone chemistry, and microclimate processes in the forest stand

atmosphere. There have been many successful applications of semiochemicals to

manage forest pests. An aerial application of verbenone in northwestern Montana significantly reduced the attack of lodgepole pine (Pinus contorta Dougl. ex Loud.) by the

mountain pine beetle (Dendroctonus ponderosae Hopkins) (Shea and others 1992).

Antiaggregation pheromones, however, have periodically failed to reduce tree attack by

the mountain pine beetle (Amman 1993, Borden 1995) and the spruce beetle (Holsten

and Werner 1985, 1987; Zogas 2001). These failures could be caused by technical

problems involving the deployment, consistent release, longevity of releasers, and dispersion of semiochemicals from the releaser, as well as the influence of the microclimate within the stand. Inconsistency in effectiveness of semiochemical applications

could lead to a reluctance of manufacturers to produce semiochemicals for operational

uses and cause forest pest managers to be hesitant to use these chemicals for pest

management strategies (Borden 1995).

The inconclusive results of semiochemical field tests indicate a need to obtain systematic knowledge on release rates from releaser devices—rates that are hypothesized

to be strongly controlled by temperatures in the field. This report describes the results

of field tests on the release of MCH (3-methyl-2-cyclohexen-1-one) and verbenone

(4-methylene-6,6-dimethylbicyclo(3.1.1)hept-2-ene) from bubble cap and bead releasers. MCH is the antiaggregation pheromone of the spruce beetle and the Douglas-fir

beetle (D. pseudotsugae Hopkins). Verbenone is the antiaggregation pheromone of the

mountain pine beetle, western pine beetle (D. brevicomis Hopkins), and the southern

pine beetle (D. frontalis Zimmerman).

The pheromones MCH and verbenone, formulated in bubble caps and beads provided

by Phero Tech, Inc. (Delta, British Columbia, Canada)1

 were placed at several field

sites in California, Oregon, and Alaska.

Darling Ridge, California—This study site was located on a southwest facing slope

in the Eldorado National Forest, about 1000 m elevation on the west side of the Sierra

Nevada. The vegetation was a mixed stand of ponderosa pine (Pinus ponderosa

Dougl. ex Loud.), white fir (Abies concolor (Gord. & Glend.) Lindl.), incense-cedar

(Calocedrus decurrens (Torr.) Florin), and California black oak (Quercus kelloggii

Newb.).

Silver Forks, California—This site was also located on the west side of the Sierra

Nevada but at an elevation of 1700 m. The overstory was diverse, dominated by white

fir, incense-cedar, and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) with sugar

pine (Pinus lambertiana Dougl.) and ponderosa pine as minor species.

Introduction

Materials and

Methods

Study Area

Characteristics

1 The use of trade or firm names in this publication is for

reader information and does not imply endorsement by

the U.S. Department of Agriculture of any product or

service.
2

Santiam Pass, Oregon—This site was located in the Cascade Range at an elevation

of 1000 m. The open canopy comprised mostly Douglas-fir 15 to 25 m tall.

Enterprise, Oregon—This site was located in the Wallowa Mountains in northeast

Oregon at an elevation of about 1500 m. A closed canopy Douglas-fir stand dominated

the site.

Cooper Landing, Alaska—This site was dominated by 100-year-old Lutz spruce

(Picea X lutzii Little) (mean diameter-at-breast-height (d.b.h.) of 30 cm) located on a

south aspect at an elevation of 300 m about 150 km south of Anchorage on the Sterling

Highway. The stand canopy was closed with an understory of 12 cm d.b.h. paper birch

(Betula papyrifera Marsh). The litter layer, about 3 cm thick, was composed primarily of

birch leaves.

Seward, Alaska—The overstory of this site was a 150-year-old closed-canopy Sitka

spruce stand (P. sitchensis (Bong.) Carr.) located on a flat area at about 300 m elevation 15 km north of Seward, Alaska, on the Kenai Peninsula. Mean d.b.h. of the spruce

was 55 cm; the understory was sparsely scattered spruce seedlings and a layer of

moss 7 cm thick.

We used MCH bubble caps with release rates2

 of 24 °C at all study locations. In addition, we used MCH bubble caps with release rates2 of 17 °C at the two Alaska sites.

These 17 °C caps are significantly more effective in the cooler Alaska temperatures

because they have a thinner membrane and thus a faster release rate than the 24 °C

caps (Werner 1994, Werner and Holsten 1995). Only verbenone releasers were placed

at the California sites.

Bubble caps were placed 2 m above the ground on the north side of trees, except in

Alaska where they were placed on the south side. Four to five bubble caps were collected every 2 weeks for laboratory analyses. Shipment was made directly to the Forestry Sciences Laboratory of the USDA Forest Service, Pacific Northwest Research

Station, in Corvallis, Oregon. Some bubble cap samples were analyzed immediately

to determine residual levels of MCH and verbenone; others were frozen and stored

for later analyses.

In addition to the bubble cap studies, MCH beads were distributed at each site on the

forest floor. Verbenone beads were distributed only at the Silver Forks and Darling

Ridge sites in California. Ten beads were randomly selected every 2 weeks from each

study site and shipped to the Forestry Sciences Laboratory.

The initial amount of semiochemical in bubble caps was provided by the manufacturer.

The best method for determining release of semiochemical from bubble caps was to

weigh the fluid content of the bubble caps brought in from the field. Simply weighing intact bubble caps was not as accurate because contaminants such as dirt, water, or

pitch could cause weight changes. The semiochemical weights were regressed against

time. Representative samples of MCH and verbenone from bubble caps from each

study site were extracted with hexane and analyzed qualitatively by gas chromatography and mass spectrometry to check for possible degradation to inactive compounds.

The MCH and verbenone beads were about 2.1 percent MCH and 2.6 percent

verbenone, respectively; the remaining mass was polypropylene polymers. Each bead

was sectioned in the laboratory with a razor blade and extracted with 1 milliliter of hexane. Concentrations of MCH and verbenone were determined by gas chromatography.

Experimental Design

Quantification of Release

Rate

2 Bubble cap release rates determined at these

temperatures by the manufacturer.
3

A more appropriate way, perhaps, to analyze the data is to estimate the actual release

rates. It is these rates that are expected to be strongly controlled by temperature. Release rates are estimated by first fitting a model to each data set and then calculating

release rates by taking the first derivative or the slope of the line generated by the datadriven model. The model that is satisfactory for all data sets is the form

y = a + bX + cXX (1)

where

X is days,

y is residual chemical in grams, and

a, b, c are parameters generated by fitting the model to the data.

The first derivative of this model is

dy/dX = b + 2cX (2)

where dy/dX is the release rate in grams per day.

If the parameter c approaches zero, the release rate is b, or is constant with time. Any

deviation from a constant release rate in the field is estimated from the value of the parameter c. Figure 18 in the appendix shows the fit of the model to each field data set for

24 °C bubble caps. Release rates are taken directly from the model lines derived for

each field site. Figure 18 is a measure of the confidence expected in the calculated release rates.

Temperature measurements were made at each study site coincident with the releaser

study. Each site had a weather station with an Omnidata data recorder (Omnidata International Inc., Logan, Utah) which received input from two exposed sensors; one

placed on the tree bole at a height near the bubble caps and the other 2 to 3 cm below

the surface of the litter layer. We thought litter layer temperatures were important factors controlling the release rates, especially in Alaska where the litter temperatures are

much lower than in warmer climates for which the beads were originally formulated.

Temperature data were collected at 2-hour intervals.

In general, MCH release rates in 24 °C bubble caps were similar at study sites in

Oregon and Alaska (Enterprise, Santiam Pass, Cooper Landing, and Seward), whereas

MCH released faster at the Darling Ridge and Silver Forks sites in California (fig. 1).

The residual MCH at the Darling Ridge site decreased especially fast compared to the

other sites. The variation in the residual MCH for the 4 to 5 caps at Darling Ridge and

Santiam Pass for each sampling period is shown in figure 17 (see app.); other sites

have similar variations.

The 17 °C bubble caps began with higher amounts of MCH and declined faster than

the 24 °C caps at the two Alaska sites (fig. 2). The residual MCH in the 17 °C caps at

the Cooper Landing site decreased more rapidly than at the other sites, whereas the

loss of MCH in the 17 °C bubble caps at the Seward site was markedly reduced after

a rapid, initial loss.

In contrast to the MCH bubble cap data, verbenone appeared to decline in a welldefined linear fashion at the Darling Ridge and Silver Forks sites (fig. 3). The rate

of verbenone loss appeared to be faster at the Darling Ridge site. The MCH loss

approached an exponential decline compared to the linear decline in residual loss

of verbenone at the Darling Ridge site (fig. 4).

Temperature

Results and

Discussion

Release from Bubble

Caps
4

Figure 1—Depletion of MCH from 24 °C bubble caps at two sites each in

California, Oregon, and Alaska. MCH was allowed to elute for 75 days in

California and 115 days in Oregon and Alaska.

Figure 2—Depletion of MCH from 24 and 17 °C bubble caps at the two Alaska

sites.
5

Figure 3—Depletion of verbenone from 24 °C bubble caps at the two California

sites.

Figure 4—Depletion of MCH and verbenone in 24 °C bubble caps at the Darling

Ridge, California, site over a 70-day release period.
6

Release rates of 24 °C MCH bubble caps at the Enterprise, Santiam Pass, Seward,

and Cooper Landing sites have similar residual chemical dynamics (fig. 5). Estimated

release rates for Santiam Pass and Cooper Landing are identical, hence only three

curves are shown in figure 5. Release rates at all four sites increased during the sampling period. The slopes, however, were not significantly different between the four sites.

Initial release rates (fig. 5) were estimated at 0.7 mg per day (per bubble cap) for all four

sites, and each increased to 1.5 mg per day at the end of the sampling period, about a

twofold increase.

In contrast to the increase in the MCH release rates shown in figure 5, there was a

steep decline in MCH release rates for Darling Ridge and Silver Forks (fig. 6). The rate

of decline was especially striking for the Darling Ridge study site. Both sites had higher

initial release rates than the sites at Enterprise, Santiam Pass, Cooper Landing, and

Seward. The initial rate for Darling Ridge was 10 mg per day (15 times greater than the

0.7 mg per day for sites in fig. 5). This initial rate of 10 mg per day declined to near zero

at the end of the sampling period. The initial release rate for Silver Forks was 5 mg per

day; it was estimated to be 2 mg per day at the end of the sampling period.

The release rates from 17 °C MCH bubble caps decreased at Cooper Landing and

Seward (fig. 7). The initial rates were different, but the rate of decline was nearly equal.

The initial release rate for the Cooper Landing site was 5 mg per day. The rate for the

Seward site, however, was slightly lower at 4 mg per day. Near the end of the sampling period, the rates were sharply reduced to 1.5 mg per day for the Seward site and

2.5 mg per day for the Cooper Landing site. These initial rates of 4 to 5 mg per day for

17 °C caps contrasted to initial rates of 0.7 mg per day for 24 °C caps at the same

sites, although the release rate for 24 °C caps rises slightly, whereas the rate for the

17 °C caps declined during the same sampling period (fig. 5).

Release rates for verbenone bubble caps were linear during the sampling period as

rates were 3 mg per day for Silver Forks and slightly higher at 4 mg per day for the

Darling Ridge site (fig. 3).

The release rate of bubble caps was expected to be strongly controlled by the temperature inside the cap. The most likely mechanism is that the chemical placed in the

bubble cap initially as a pure liquid vaporizes into the atmosphere within the bubble cap

and then releases through the membrane into the stand atmosphere. Vaporization may

possibly occur on the exterior membrane surface. This, however, was not explored.

The vapor pressure inside the bubble cap was close to the saturation vapor pressure,

whereas the vapor pressure outside the membrane was negligible because the chemical was quickly removed by atmospheric turbulence, especially during the warm turbulent periods when beetle flight occured. Release rates, therefore, were controlled by the

saturation vapor pressure and the conductance of the membrane. Membrane conductance remained constant unless the membrane integrity was somehow disrupted, but

the saturation vapor pressure increased exponentially with temperature.
7

Figure 5—Model results of release

rates from 24 °C MCH bubble caps at

the Oregon and Alaska sites over a

100-day release period.

Figure 6—Model results of release rates from 24 °C MCH bubble caps for the

two California sites.
8

Figure 7—Release rates from 17 °C MCH bubble caps from the two Alaska sites.

Table 1—Comparison of mean (+ standard deviation) litter layer and air

temperatures for all study sitesa

Date

Site 1996 Air temperature Litter temperature

– – – – Degrees centigrade – – – –

Darling Ridge 6/23 to 9/1 23.6 + 5.1 21.3 + 2.6

Silver Forks 6/23 to 9/1 18.4 + 7.5 16.3 + 3.1

Santiam Pass 5/6 to 8/25 14.2 + 6.1 13.5 + 4.0

Enterprise 4/28 to 6/9 9.2 + 5.7 7.7 + 2.7

8/4 to 9/19 15.4 + 5.7 14.0 + 2.9

Seward 5/17 to 8/11 10.3 + 4.7 8.8 + 2.7

Cooper Landing 5/17 to 8/10 11.9 + 4.5 9.8 + 3.1

a

 Means and standard deviations calculated from data collected every 2 hours.
9

The hypothesis is that the differences in the field release rates (shown in figs. 1 through

7) can be explained by temperature differences. Table 1 is a compilation of the average

daily air and litter layer temperatures for the six study sites. The sites in California

(Darling Ridge and Silver Forks) had considerably warmer temperatures than the other

sites, 23.6 and 18.4 °C, respectively. These temperatures explained the high initial release rates at these sites because release rates increased exponentially with temperature. The Oregon Douglas-fir sites had lower temperatures than the California pine

sites, but somewhat higher temperatures than the Alaska spruce sites. Oregon and

Alaska sites had release rates that were not significantly different from each other, although the average temperatures seem to be significantly different. At lower temperatures, release rates varied less with temperature. Rates were still affected by

temperature, but the magnitude was more difficult to demonstrate with field data.

A more detailed analysis can be done by using the air temperature data collected every

2 hours at each location. Darling Ridge and Cooper Landing sites had the largest differences in temperature (fig. 8, 9). For Darling Ridge (fig. 8), there was no discernible

seasonal trend. Temperatures remained between 15 and 35 °C during the sampling

period (including day and night measurements). At the Cooper Landing site (fig. 9),

there was an increase in temperature during the May, June, and July sampling periods.

This probably explained the observed increase in release rates (fig. 5). For Darling

Ridge, the high initial release rates (fig. 6) were likely the result of high temperatures;

the decrease in release rates occured although the temperature remained high. This

decline probably occured because the chemical in the bubble cap was being depleted

to a level where the vapor pressure inside the cap was diminished, thereby causing a

reduction in the vapor pressure deficit between that inside the cap and the atmosphere

external to the membrane. The Silver Forks site had temperatures similar to the Darling

Ridge site, and the same analysis applies. The Seward, Santiam Pass, and Enterprise

sites were similar to the Cooper Landing site in their dynamics.

It is significant that the release rates of verbenone at the Darling Ridge and Silver Forks

sites were constant over the sampling period, whereas the MCH bubble cap release

rates declined dramatically. Both releasers experienced the same temperature regime.

The difference was that nearly twice as much chemical was initially placed in the

verbenone releaser as in the MCH releaser. This suggests that the low release rates of

MCH near the end of the sampling period at the two California sites were caused by

high temperatures, which in turn caused rapid initial release rates and depleted the

MCH, subsequently causing lower release rates later in the season. Another possibility

is that there was a difference in volatility between the two compounds that could affect

release rates.

The 17 °C MCH bubble caps at the Cooper Landing and Seward sites also exhibited a

decline in release rates, while at the same time there was an increase in release rate of

the 24 °C MCH bubble caps that were at the same site with the same temperature regime. The 17 °C release device has a thinner membrane than the 24 °C release device. Again, this may have been the result of rapidly declining levels of MCH within the

bubble cap, therefore reducing the release rate in the later stage of the study. This reduction in release rate would not be expected to be linear over the course of the study,

but the field sampling frequency may not have been sufficient to define the nonlinearity.
10

Figure 8—Air temperature (°C) at 2-hour intervals, Darling Ridge, California.

Figure 9—Air temperature (°C) at 2-hour intervals, Cooper Landing, Alaska.
11

There was no residual verbenone found in beads analyzed after 2 weeks in the field

from either the Darling Ridge or Silver Forks sites. Either the active compound released

completely from the bead during this period or degraded down to an inactive derivative.

This is in contrast to the results obtained from an aerial application of verbenone beads

in northwestern Montana (Shea and others 1992). In this study, more than half the

verbenone was available for release from the beads after 2 weeks.

The seasonal decline in residual MCH in the beads for each of the six study sites was

more variable than the MCH or verbenone bubble cap data, primarily because the initial concentration of MCH in the beads had a much higher variation than in the bubble

caps (figs. 10, 11, and 12). The mean initial mass of MCH per bead was 0.835 mg +

0.181 mg at one standard deviation—the lowest amount observed was 0.384 mg and

the highest was 1.16 mg. This large variation did not, however, mask the rapid initial

decline in MCH content at all study sites. Figure 10 compares the warmest California

site, Darling Ridge, with the Alaska Cooper Landing spruce site. In both cases, there

was a rapid initial decline in the amount of MCH in the beads, followed by a constant

amount of MCH. That is, the rapid initial decline was exponential in nature; the leveling

off indicates there was no release after this rapid decline. The same dynamics occurred

at the other study sites, with some variation in the decline rate and the amount of MCH

remaining in the bead (figs. 11 and 12).

To help quantify these results, an exponential model has been fitted to the data. The

lines in figures 10 through 12 are the fit of the model to the data. The model form is:

Y = A + B * exp (-C * X) (3)

where

Y = residual MCH in milligrams,

X = days after bead dispersion,

A, B, C, are estimated parameters,

A + B estimates the initial MCH in the beads (mg),

A estimates the residual MCH after the rapid initial decline (mg), and B and C determine the release rate; B is the scaling parameter (mg), and C is the exponential parameter (per day).

This model form appears to adequately represent the MCH residual dynamics for all six

study sites. Table 2 is a summary of the estimated parameters for each site.

The exponential parameters, which are indicators of the initial decline rate, are the

most negative for the warm California sites, Darling Ridge and Silver Forks, thereby

indicating the most rapid rate of loss. The remaining four sites have loss parameters

that are nearly equal. These four sites, Enterprise, Santiam Pass, Seward, and Cooper

Landing, had litter layer temperatures considerably below those at the California sites

(table 1).

The initial amount of MCH in the beads was measured directly at the beginning of each

experiment and is reflected in the model by the sum of the constant (A) and scaling (B)

parameters. This sum has only the variation found inherent in the MCH content of

beads provided by the manufacturer.

Release from Beads
12

Figure 10—Depletion of MCH from beads from Darling Ridge, California, and Cooper

Landing, Alaska, for 100 days.

Figure 11—Depletion of MCH from beads from Silver Forks, California, and Seward,

Alaska, for 100 days.
13

Figure 12—Depletion of MCH from beads from Enterprise and Santiam Pass,

Oregon.

Table 2—Parametersa from models of residual MCH in beads

Residual MCH (mg) Scaling (mg) Exponential (per day)

Site A B C

Darling Ridge, CA 0.17 0.70 0.10

Silver Forks, CA .10 .80 .15

Enterprise, OR .12 .70 .05

Santiam Pass, OR .18 .65 .065

Seward, AK .25 .8 .07

Cooper Landing, AK .5 .6 .07

a

 A estimates the residual MCH after the rapid initial decline (mg); B is the scaling parameter (mg); and C is

the exponential parameter (per day).
14

The constant parameter (A) estimates the residual MCH found in the beads after the

rapid initial decline; after this amount was reached, the data suggest there was no further release. The sites in California and Oregon had similar amounts, whereas the

Alaska sites had higher amounts. The Cooper Landing spruce site showed high residual, 0.5 mg, which is about 50 percent of the initial MCH in the beads, similar to previous findings in Alaska (Holsten and Werner 1985). For some reason, the total amount

of MCH in the beads was not releasing, and this amount seemed somewhat temperature dependent—lower temperatures resulted in a higher amount of MCH not available

for release. This conclusion should be considered preliminary because there is considerable variation in the data. With the bead and similar plastics, MCH is within a

substrate composed of a framework of interlocking polymer molecules that expand in

higher temperatures and contract at lower temperatures. The beads are loaded by

heating them in the lab and then soaking or spraying them with MCH3

. This would be

consistent with the high variation noted in the pheromone load of the beads and the

higher retention of residual MCH in colder environments. Thus the short-term release

of a pheromone from beads followed by no release may be a function of the initial

amount of pheromone on the bead surface and not from the polymer matrix.

In analyzing the effect of temperature on release rate of beads, it was apparent that

only the litter layer temperatures during the first 20 days were controlling the release

of MCH. The average litter layer temperature for each site for the first 20 days of each

study is presented in table 3. (See table 1 for the appropriate calender period). To estimate release rates for this 20-day period, the original model (equation 3) is modified

by taking the first derivative. The result is a variable release rate for each site with the

highest rates occurring immediately after the beads have been dispersed. The release

rate then declines in an exponential fashion. In quantitative terms, beads released

MCH proportional to the amount of MCH in the bead—as the amount of MCH in the

bead declined, the release rate declined. Rates, calculated for 50 percent of total MCH

released, were between 0.01 and 0.04 mg MCH per day. There was a positive temperature effect between the release rate relative to average litter layer temperature

(table 3), but the relation was marginal; the correlation coefficient was 0.6 (fig. 13).

Higher temperatures resulted in higher release rates, with an increase in release rate

of 0.0008 mg per degree.

This study revealed that beads release their contents only during the first 2 to 3 weeks

following their dispersal, and this may, or may not, coincide with bark beetle flight.

Figures 14 to 16 show the period of active beetle flight for Seward, Cooper Landing,

and Enterprise. Insect activity periods are defined as those periods when the air temperature is above 16 °C (these periods are indexed as 1 in figs. 14 through 16). For the

Alaska sites, the index indicated no bark beetle activity for the first 10 days, whereas

at Santiam Pass, there were periods during most days when temperatures exceeded

16 °C. (Enterprise, Darling Ridge, and Silver Forks were similar to Santiam Pass.) For

the Alaska sites, it seemed that the period of the most rapid release of MCH from the

beads probably would not have coincided with bark beetle flight. At the other sites, the

beads could only be potentially effective for short periods after dispersion.

3 Daterman, Gary. 2001. Personal communication.

Entomologist, Pacific Northwest Research Station,

Forestry Sciences Laboratory, 3200 SW Jefferson Way,

Corvallis, OR 97331.
15

Table 3—Mean litter layer temperatures for

20 days after bead dispersion

Site Temperature

Degrees centigrade

Darling Ridge, CA 21.2

Silver Forks, CA 15.2

Santiam Pass, OR 9.3

Enterprise, OR 7.1

Seward, AK 4.5

Cooper Landing, AK 5.6

Figure 13—Release rate from beads related to average litter layer

temperature (°C) for first 20 days after the beads were dispersed.
16

Figure 14—Estimated periods of insect activity at Seward, Alaska,

related to the number of days after beads were distributed. Values of 1

are periods of temperature greater than 16 °C.

Figure 15—Estimated periods of insect activity at Cooper Landing,

Alaska, related to the number of days after beads were distributed.

Values of 1 are periods of temperature greater than 16 °C.
17

The results of this study demonstrated that the release rates of MCH and verbenone

bubble cap releasers are controlled by temperature and will vary significantly from

warm sites to cool sites. Release rates from bubble caps were likely controlled by the

membrane composition and thickness, along with internal vapor pressure. The latter

was strongly correlated with ambient air temperature. The MCH and verbenone beads

released their contents only during the first 2 to 3 weeks after their dispersal, regardless of the study location. To be effective, it is important that MCH and verbenone be in

the atmosphere during beetle flight. Thus, more than one application of MCH or

verbenone beads may be needed if the beetle flight period lasts more than 2 weeks.

The results of this study demonstrate the importance of determining field release rates

of pheromone dispensers. Limited understanding of field release rates will lead to inconclusive results and confusion in pheromone field tests that rely on these chemicals

for pest management strategies.

We thank Ken Zogas, U.S. Department of Agriculture, Forest Service, Forest Health

Protection, Anchorage, AK, for help during plot establishment and data acquisition. We

thank Dr. Lonnie Sower, research entomologist (retired), U.S. Department of Agriculture, Forest Service, Pacific Northwest Experiment Station, Corvallis, OR, for his initial

efforts in the design and establishment of this project. We also thank Dr. Mike Haverty,

Figure 16—Estimated periods of insect activity at Santiam Pass, Oregon, related to

the number of days after beads were dispersed. Values of 1 are periods of

temperature greater than 16 °C.

Conclusions

Acknowledgments
18

research entomologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station, Albany, CA; Iral Ragenovich, entomologist, U.S. Department of

Agriculture, Forest Service, State and Private Forestry, Portland, OR; and Dr. Harold

Thistle, Forest Meteorologist, U.S. Department of Agriculture, Forest Service, Forest

Health Technology Enterprise Team, Morgantown, WV, for their helpful technical reviews.

When you know: Multiply by: To find:

Celsius (°C) 1.8 and add 32 Fahrenheit

Centimeters (cm) 2.54 Inches

Hectares (ha) 2.47 Acres

Kilometers (km) 0.621 Miles

Meters (m) 3.281 Feet

Square meters (m2

) 1.20 Square yards

Millimeters (mm) 0.254 Inches

Amman, G.D. 1993. Potential of verbenone for reducing lodgepole and ponderosa

pine mortality caused by mountain pine beetle in high-value situations. In: Shea, P.J.

tech. coord. Proceedings of the symposium on management of western bark beetles

with pheromones: research and development. Gen. Tech. Rep. PSW-GTR-150.

Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest

Research Station: 33-37.

Borden, J.H. 1995. From identifying semiochemicals to developing a suppression

tactic: a historical review. In: Salom, S.M.; Hobson, K.R., eds. Proceedings of the

national Entomological Society meeting: application of semiochemicals for management of bark beetle infestations. INT-GTR-318. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station: 3-10.

Holsten, E.H. 1994. The role of spruce beetle pheromones as management strategies

in Alaska. In: Shea, P.J., tech. coord. Proceedings of the symposium on management of western bark beetles with pheromones: research and development. Gen.

Tech. Rep. PSW-GTR-150. Albany, CA: U.S. Department of Agriculture, Forest

Service, Pacific Southwest Research Station: 11-14.

Holsten, E.H., Werner, R.A. 1985. Evaluation of a controlled release formulation of

Methylcyclohexenone (MCH) in preventing spruce beetle attacks in Alaska. Tech.

Rep. R10-9. Anchorage, AK: U.S. Department of Agriculture, Forest Service, Forest

Pest Management, Alaska Region. 9 p.

Holsten, E.H., Werner, R.A. 1987. Use of MCH bubble caps in preventing spruce

beetle attacks in Alaska. Tech. Rep. R10-14. Anchorage, AK: U.S. Department

of Agriculture, Forest Service, Forest Pest Management, Alaska Region. 12 p.

Matthews, K.; Wittwer, D.; Zogas, K. [and others]. 1997. Forest insect and disease

conditions in Alaska—1996. Gen. Tech. Rep. R10-TP-67. U.S. Department of

Agriculture, Forest Service, Alaska Region. 42 p.

English Equivalents

Literature Cited
19

Shea, P.J. 1995. Use of insect pheromones to manage forest insects. In: Biorational

pest control agents. [Publisher unknown]. American Chemical Society Symposium

Series: 272-283. Chapter 20.

Shea, P.J.; McGregor, M.D.; Daterman, G.E. 1992. Aerial application of verbeneone

reduces attack of lodgepole pine by mountain pine beetle. Canadian Journal of

Forest Research. 22: 436-441.

Werner, R.A. 1994. Research on the use of semiochemicals to manage spruce beetles

in Alaska. In: Shea, P.J., tech. coord. Proceedings of the symposium on

management of western bark beetles with pheromones: research and development.

Gen. Tech. Rep. PSW-GTR-150. Albany, CA: U.S. Department of Agriculture, Forest

Service, Pacific Southwest Research Station: 15-21.

Werner, R.A.; Holsten, E.H. 1995. Current status of research with the spruce beetle,

Dendroctonus rufipennis. In: Salom, S.M.; Hobson, K.R., eds. Proceedings of the

national Entomological Society of America meeting: application of semiochemicals

for management of bark beetle infestations. Gen. Tech. Rep. INT-GTR-318. Ogden,

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station:

23-29.

Zogas, K. 2001. Summary of thirty years of field testing of MCH: antiaggregation

pheromone of the spruce bark beetle and the Douglas-fir beetle. Tech. Rep.

R10-TP-91. U.S.Department of Agriculture, Forest Service, Alaska Region. 27 p.
20

Figure 17—Two examples of data variation for MCH bubble cap release rates. Sites are

Darling Ridge, California, and Santiam Pass, Oregon. Lines are model fit to the data.

Appendix
21

Figure 18—Comparison of MCH residue data in bubble caps and model fit for each of the six field sites.
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