Forest Health Protection – Intermountain West 

Many species of bark beetles are 

causing widespread tree mortality 

throughout the Intermountain West. 

Although sometimes viewed by humans as catastrophic, outbreaks 

of native forest insects are natural events. Native insects and the plants they use 

for food and reproduction have evolved together. Unlike some introduced pests, native insects 

kill individual trees but do not threaten the existence of an entire plant species. Native insect 

outbreaks are only a problem when they conflict 

with values that humans have for an area (i.e., 

recreation, wildlife habitat, scenic beauty, wood 

production or property values). A tree in the wilderness is not subject to the same human values 

as a tree in your backyard.

Bark beetle populations have been increasing in forested areas of the western U.S. The primary reason for this increase is the combination 

of large areas with susceptible stand conditions 

(mature trees in dense stands) and trees stressed 

by drought. High levels of forest insect activity 

will likely continue if current conditions do not 

improve.

The bark beetles causing widespread mortality in the forests of the Intermountain West 

are all native. The principal species include: 

mountain pine beetle, spruce beetle, Douglas-fir 

beetle, fir engraver beetle, western balsam bark 

beetle, and pinyon ips.

 They’re Back!!

Are my trees at risk?...............................page 2

Have my trees been attacked?.........page 5

How to prevent Attacks ........................page 6

What is a bark beetle?............................page 8

Does this affect you? Look inside

Bark Beetles

Are Your Trees at Risk?

➠

Individual beetles of these species are not 

much larger than a piece of cooked rice. Not only 

are they small, brown, and hard to see, but much 

of the time their activity is scattered and barely 

noticeable.

In low numbers (latent populations) these insects survive on newly dead, dying or stressed 

trees created by wind, snow, lightning, other biotic organisms, or by human activity. Occasionally, small pockets of standing trees may be killed 

but over the landscape these patches are often unnoticed. 

However, beetle population levels can increase when sufficient food is available, allowing 

large numbers of these small beetles (outbreak 

populations) to attack large healthy trees en mass. 

Often many trees are killed over the landscape 

with results likened to that of wildfire. In recent 

years, more trees have been killed by bark beetles 

than by fire!

In the battle between trees and tree-killing beetles the two principle interacting factors 

are tree vigor and beetle numbers. When beetle 

populations are low, healthy trees often produce 

enough resinous pitch to drown and flush out the 

beetles that attempt to enter (pitchout). When 

trees are stressed they may be unable to produce 

sufficient amounts of defensive pitch. Yet, when 

beetle populations are high, even a healthy tree 

may not be able to produce enough pitch to ward 

off hundreds of simultaneous attacks (a mass attack). In addition, many beetles carry fungi that 

further damage the tree’s defense system. 

How can something so small

kill something so big?

What causes similar attacks? ...........page 9

What are land managers doing? .....page 11

Who Should I Contact?............................page 12

Forest

Health

Protection

The USDA Forest Health Protection offices in 

Ogden, UT and Boise, ID, in cooperation with the 

Caribou-Targhee and the Bridger-Teton National Forests have created this publication to educate the public regarding the principle tree-killing 

bark beetles in the Intermountain West. With this 

knowledge, you can make informed decisions 

concerning protection of your private property 

and provide meaningful input about proposed actions on public lands.

Representatives from the cooperating agencies 

are available to assist you with additional information. Please see page 12 for a list of contacts 

and additional information sources.

DOUGLAS-FIR mortality (outbreak)

A ‘Pitchout’

A Douglas-fir beetle

Fading trees attacked by bark beetles
Forest Health Protection – Intermountain West

Step 1: Identify Your Trees

The first step in determining whether or not your tree is susceptible to insect attack is to know what species of tree you have. The following lists are the 

principal evergreen species found in the Intermountain West.

Are Your Trees at Risk to Bark Beetles?

What Should You Do?

Lodgepole

Needles are two per bundle, 1-3" long. The small 3⁄4-2" long cones 

have very short stalks and stay attached to the tree for many years. 

Cones feel prickly.

Natural Range: ID, MT, WY, northern UT, spots along the Sierra 

Nevada Range in NV.

Pines (native): 

PINYON (Colorado and Singleleaf)

Colorado pinyon, found mainly in Utah have two, 1-2" long needles per bundle. Singleleaf pinyon, found mainly in Nevada, have one 

sharp, rounded needle per bundle, >1" long. Cones are not spiny.

Natural Range: Colorado pinyon in UT; Singleleaf pinyon in NV, 

western edge of UT, scattered spots in southern ID.

PONDEROSA (and Jeffrey)

Ponderosa needles are 2-3 to a bundle, ranging from 3-10" in length. Cones are 2-6" long and 

prickled. Jeffrey pine (3-needles) is found along the Sierra Nevada’s, overlapping with ponderosa 

pine’s broad range. Jeffrey generally has larger, stouter cones (5-9") with incurved spines (pokey 

ponderosa; gentle Jeffrey).

Natural Range: ID, MT, UT, spots in eastern NV and the Sierra Nevadas, isolated spots in 

WY.

5-NEEDLED (e.g. limber, 

white bark, and western 

white pines)

Several pine species with 5-needle bundles are native to the Intermountain West, 

but Limber is the more commonly planted 

species around homes. Needle length ranges 

from 1.5-4". Cones vary.

Natural Range: various throughout Intermountain West.

Most pines have more than one needle attached to the tree together in a ‘bundle.’ The 

number of needles per bundle is often important in determining the pine species.

Closed and open cones

Foliage with MALE and 

female CONES

SIngleleaf pinyon

Colorado pinyon

oPEN PONDEROSA CONES

cLOSED PONDEROSA CONES 

AND LONG NEEDLES

lIMBER PINE NEEDLES AND CONES
Forest Health Protection – Intermountain West 

Engelmann and Blue 

Spruce

Single needles are square and sharp, 

leaving ‘bumps’ on the small twigs when 

they fall off. Blue spruce needles tend to 

be stiffer and sharper than Engelmann 

needles. Cones hang down, measuring 1-

2.5" in length for Engelmann and 2.5-4" 

for blue. In the wild, blue spruce prefers 

moist stream edges.

Natural Range: Engelmann spruce in 

ID, MT, WY, UT, and NV; blue spruce in 

UT and WY.

Subalpine fir

The short (1-1.5"), single, flat needles 

also have rounded tips but are thick at their 

base (vs. white fir). The dark purple cones 

(2.25-4" long) are borne upright on the upper branches and are not dropped. 

Natural Range: ID, western MT, western WY, UT, spots in northern NV.

Douglas-fir

Although not a true fir species, Douglas-fir is 

similar to other firs in having short (~1"), single, 

flat needles. Needles have rounded tips like white 

and subalpine fir, and are narrow at their base like 

white fir. However, the 3" long cones hang down. 

The cone scales have a distinct shape resembling 

the tail and back legs of a mouse.

Natural Range: ID, MT, WY, UT, and scattered spots in NV.

Pines (exotic):

FIRS (native): SPRUCES (native):

WHITe fir

The 2-3" long, single, flat needles narrow to a stalk at their base and have rounded tips (vs. sharp spruce or notched grand 

fir). The needles tend to curve upward, leaving few needles below the stem. The greenish purple or yellow cones (3-5"), found in 

the upper branches, point up and are not 

dropped. Rather, they fall apart on the tree 

(vs. Douglas-fir cones that drop off).

Natural Range: UT, eastern NV, southeast corner of ID.

SCOTCH AND AUSTRIAN PINES

These European pines have 2-needles per bundle, 1.5-3" and 3-6" 

longs, respectively. Scotch cones are smaller (1.5-2" long) than Austrian cones (2-3"). Cones of both species are not spiny (vs. ponderosa). 

Scotch pine is noted for the strong orange coloration of the bark. 

Natural Range: As exotic species there is no native range but they 

can be found planted throughout the Intermountain West.

References:

• Kuhns, Michael. 1998. A guide to the trees of Utah and the Intermountain West. Utah State University Press, Logan, UT

• National Audubon Society. 1996. Field Guide to North American 

Trees. A. A. Knopf, NY

• Watts, Tom. 1985. Rocky Mountain Tree Finder. Nature Study 

Guild, Rochester, NY

GRAND FIR

The single, flat needles of grand fir 

are 1.25-2 inches long and distinguished 

by having a notched end. Needles tend to 

grow out to the sides giving the branchlets a flattened appearance. Cones are 

also 2-4" long, green-brown in color, and 

extend upward. 

Natural Range: 

northern 

half of ID, 

northwest 

edge of 

MT.

Firs and spruce have only one needle (no ‘bundles’) 

but the shape of that needle can differ by tree species.

Cones

Foliage and buds

Austrian pine

Scotch pine

Engelmann

Young cones

Blue

Cones

Foliage

Upright 

cones stay on 

branches

Upright cones stay 

on branches

Foliage
 Forest Health Protection – Intermountain West

Step 2:

Determine Your 

Trees’ Susceptibility

The susceptibility of an individual tree is often described differently than the susceptibility of a stand of trees. When there is a group of 

trees (a stand), a tree may be killed yet the overall stand may look and function much as before. 

In an urban setting, however, an individual tree 

may be of high importance for aesthetic or other values.

INDIVIDUAL TREE SUSCEPTIBILITY

Trees that are stressed are less able to produce the pitch used to counter bark beetle attacks. Damage to the bark, needles, or root 

system can occur through human activity (construction, paving, excavating, etc.) or by natural causes (drought, wind, lightning, other insect 

or disease 

agents, etc.). 

The more 

stressed the 

tree is the 

more susceptible it 

may be. Poor 

crown condition is often 

an indication 

of stress.

Susceptible trees are 

not always 

attacked by 

bark beetles, especially if beetle numbers are 

low. Conversely, it is possible that when beetle 

populations are high, even healthy trees may be 

attacked.

STAND SUSCEPTIBILITY

Dense stands are more susceptible than open 

stands where trees do not have to compete with 

each other for limited water, light, and nutrients. 

Stands with a higher diversity of tree ages and 

tree species are also less susceptible. Some tree 

cover will likely remain if a bark beetle outbreak 

does remove the most susceptible trees.

Stands that have trees stressed by drought, 

defoliation, disease, or other damage are especially susceptible to bark beetle attacks.

SPECIFIC TREE SUSCEPTIBILITIES

Tree-killing bark beetles often have a preference for specific tree species. In some cases, a 

beetle species will attack only one tree type. In 

other cases the beetle may be able to use a number of similar tree species. 

Lodgepole, ponderosa, ‘5-needled’ pines, 

and other introduced and native pines: All 

native and introduced pines, except for Jeffrey 

pine, are susceptible to the mountain pine beetle. 

Jeffrey pine is susceptible to the Jeffrey pine 

beetle which is very similar to the mountain pine 

beetle. The most susceptible pine trees are older 

than 80 years; greater than 8 inches in diameterat breast height; weakened by drought, disease 

or damage (e.g. lightning or windthrow); or located near existing beetle-infested trees. Recently dead or downed pines are rarely infested by 

mountain pine beetle. However, there are other 

beetles that will use this material and can cause 

small clusters of tree mortality if conditions are 

right (especially Ips species).

Singleleaf and Colorado pinyons: Although several bark beetles can utilize pinyon 

pine, the landscape level mortality noted in recent years has been caused by pinyon ips. Trees 

stressed by drought, defoliation, pruning, or other damage are highly susceptible, especially if 

the trees are stressed in the spring or early summer. Drought is the principle instigator of outbreaks. 

Engelmann and blue spruce: Engelmann 

is the preferred host tree species for spruce beetle with blue spruce occasionally attacked and 

successfully infested. Engelmann spruce trees 

over 16 inches in diameter are most susceptible to spruce beetle; trees less than 5 inches in 

diameter are seldom attacked. Freshly killed 

or damaged trees (e.g. from windthrow or avalanches) are preferred habitat. In this material beetles may be able to build a large population that can overcome the defenses of healthy 

host trees.

Douglas-fir: Douglas-fir trees can be killed 

by the Douglas-fir beetle. The most susceptible 

trees are larger than 14 inches in diameter; older 

than 120 years; growing in dense stands; weakened by drought, root disease, or defoliation; or 

are located near existing beetle-infested trees. 

The Douglas-fir beetle will readily use recently downed or damaged material and has shown a 

strong preference for fire-scorched trees.

White fir: The principle bark beetle in 

white fir is the fir engraver beetle. Large diameter trees weakened by drought, defoliation, or 

other stressors are most susceptible. Root disease is often associated with white fir and serves 

as a weakening agent. In some cases, only parts 

of trees are killed (especially tops).

Grand fir: Stressed trees over 5 inches in 

diameter are particularly susceptible to fir engraver. Odors emitted from stressed trees appear 

to be the principal attraction for attack. Overcrowding, disease, defoliation, and drought often cause stress. In grand fir forests, pure, dense 

stands are most susceptible. Because fir engraver may only kill a portion of the tree, a tree may 

sustain attacks over several years before tree 

mortality occurs. 

Subalpine fir: Subalpine fir trees are also 

susceptible to the fir engraver beetle. However, 

western balsam bark beetle is the more common 

bark beetle in subalpine fir, and prefers highly 

stressed trees, especially those infected with root 

disease or weakened by drought. Windthrow 

events can also cause western balsam bark beetle outbreaks. Often a complex of factors including root disease, drought and bark beetles together cause widespread or pockets of subalpine 

fir mortality. 

A thinned stand with a 

diversity of tree ages

A dense stand with trees 

competing for resources

Crown differences

between a healthy (left) 

and stressed (right) tree
Forest Health Protection – Intermountain West

Step 3:

Determine if Your 

Trees Have Been 

Attacked

Many symptoms of bark beetle attack are similar regardless of the tree or beetle species involved. However, some are more prevalent with 

certain bark beetles than others. Some of the 

most common signs are described below. 

Mountain (and Jeffrey) Pine 

BeetleS

HOSTS: Most native and introduced pine 

species, except Jeffrey 

pine which is 

attacked by 

the very similar Jeffrey pine 

beetle. Pinyon 

pines are not 

commonly attacked.

Pine trees infested with mountain pine beetle (or Jeffrey pine beetle) become next year’s 

infection source, so it is important to identify freshly attacked trees. Signs of beetle infestation are pitch tubes or small holes and boring 

dust. Most beetle-attacked trees will have pitch 

tubes scattered over the bole of the tree. These 

popcorn-shaped masses of pitch and boring dust 

may be brown, pink, yellow or white. If the tree 

is extremely water stressed and cannot produce 

pitch, only small holes and boring dust are visible. Removing a section of the bark should 

show tunnels created by beetles in their reproduction (see page 8) if the attacks were successful. Downed host trees are rarely attacked by 

mountain pine beetle but may be attacked by another bark beetle group called ‘ips’. The ips do 

not typically kill healthy live trees. Gallery patterns of all ips species are similar (see pinyon 

ips on page 9) and differ from that of mountain 

pine beetle.

Douglas-fir Beetle

HOSTS: Douglas-fir.

Trees that have been infested will generally remain green until the following spring, so 

you must look for “clues” other than dead foliage. These trees become next spring’s infection source, so it is important to identify them. 

Fresh-down trees and fire scorched trees are 

highly susceptible. 

 The most reliable external sign that your 

tree has been attacked is the presence of boring dust (reddish-brown 

sawdust) in 

bark crevices or around 

the base of 

the tree from 

April to August. Boring 

dust is created when the 

insects bore 

through the 

bark of the 

tree. Multiple pitch streams about 20 feet up on the tree 

bole may also be an indicator. However, not all 

pitching means bark beetles are present. Removing a section of the bark may show tunnels created by beetles in their reproduction process (see 

page 8). Unfortunately, sometimes the tunnels 

are made at heights on the tree that are beyond 

your reach.

Spruce Beetle

HOSTS: Principally Engelmann spruce although blue spruce may be occasionally attacked.

Signs of attack are boring dust (see photo 

under Douglas-fir beetle) 

in bark crevices or around 

the base of the 

tree from midMay to July. 

Pitch tubes 

may accumulate around 

the insect boring holes. 

Also, look for 

pieces of bark 

around the 

base of the tree. Woodpeckers will often flake 

off pieces of this thin barked tree in order to 

feed on the beetles and their larvae. Removing 

a section of the bark should show tunnels created by beetles in their reproduction process (see 

page 8) if the attacks were successful.

PINYON IPS

HOSTS: Singleleaf pinyon, common pinyon, other pinyon species, and occasionally other pines.

Pinyon ips attack all species of pinyon and 

occasionally other types of pines if they occur 

around the pinyon trees. Crown fading is often 

the first noticeable sign of attack. Small pitch 

tubes and boring dust may be present but are not 

easily noticed on bushy trees. Attacks can occur from early spring through late summer since 

this bark beetle can have several generations in 

a year. Woodborers also will quickly infest dead 

or dying trees, but can be differentiated by their 

larger size and a lack of distinct ‘ips’ gallery pattern (see page 9).

FIR ENGRAVER

HOSTS: White fir, grand fir, and occasionally subalpine fir.

Fir trees are often attacked in groups with 

attacked trees usually 5 inches in diameter or 

greater. Trees generally turn yellow-red within 

3-6 months. Evidence of attack before trees fade 

is often hard to detect; entrance holes are without pitch tubes and in the Intermountain West 

pitch streamers are rare. Boring dust in bark 

crevices and color fading are most noticeable. 

This beetle may attack only strips or portions of 

the tree which will not cause mortality of the entire tree. These partial attacks may result in dead 

branches or tree tops. If your tree is fading and 

you think it might be caused by fir engraver beetle, check for the distinct gallery pattern the beetle creates under the bark (see page 9).

WESTERN BALSAM BARK 

BEETLE

HOSTS: Subalpine fir.

External evidence of successful attacks by 

western balsam bark beetle can be hard to detect. Entrance holes and boring dust may be visible in late summer. Pitch flow may be found, especially when attacks have not been successful. 

Successfully attacked trees turn yellowish-red 

within a year and can stay bright red for several 

years after death.

Top kill and tree mortality 

caused by fir engraver

Pitch streaming

Woodpecker feeding

Red boring dust

on tree bark

Pitch tubes
Forest Health Protection – Intermountain West

Step 5: How to 

prevent Bark Beetle 

attacks

There are several things you can do to protect 

your trees from bark beetles. Preventing attack is 

key because you cannot do anything to save a tree 

once it has been successfully attacked.

1. Remove all trees that currently contain beetles 

as described in Step 4.

2. Always clean up any recently blown down 

trees or fresh slash over 4 inches in diameter. 

Beetles are more attracted to and reproduce 

better in large diameter slash material.

3. Avoid tree damage such as knocking off bark, 

or compacting/excavating soil near trees. Injured trees attract bark beetles.

4. Thin out dense 

stands of trees, 

leaving the 

healthiest, most 

vigorous ones. 

Contact your 

state forester 

(see page 12) 

for details on 

proper thinning 

methods. Trees that have less competition for 

water, light, and nutrients more effectively repel bark beetle attacks. Thinning can also hamper the bark beetle pheromone communication 

system that facilitate mass attacks.

5. Increase age and species diversity to enhance 

stand resistance to bark beetle attacks and reduce the effects of tree mortality when attacks 

occur.

6. Use commercially produced beetle pheromones 

to inhibit attraction to an individual tree or a 

stand. Presently, this method is only available 

for deterring mountain pine beetle and Douglas-fir beetle under some situations. 

7. Use insecticides to protect unattacked trees. 

Carbaryl spray applied as a preventative treatment is effective for most bark beetles, but is 

not registered for use against fir engraver or 

western balsam bark beetle.

I

f enhancing wildlife habitat interests you, consider keeping dead trees on your forested 

lands. Standing dead trees in a forest are called “snags” and many species of wildlife depend on snags for their survival. 

Owls, hawks, and eagles use snags to perch and to support their nests. Cavity nesters such 

as woodpeckers, mountain bluebirds, and chickadees nest in the snag cavities.

Chipmunks, squirrels, and other mammals use snags as homes. Bats use areas under loose 

bark for roosting. Fungi, mosses, and lichens commonly grow in the decaying wood of a snag.

Insects chew through the decaying wood, creating tunnels and chambers. Moths and ladybird beetles, and many species of reptiles and amphibians, hide under the bark of snags. 

With so many animals and plants living on and in a dead tree, other animals frequently 

come there to feed. For example, many species of woodpeckers depend on snags to provide 

insect larvae for food.

If a tree on your private land does not have the potential to endanger persons or property, 

please consider leaving it standing for our animal friends! 

Step 4: How to Treat Trees That Have 

Been Attacked

Once bark beetles have attacked a tree around more than half of its circumference, there is 

generally nothing you can do to save it. There are no chemical insecticides registered or recommended for killing bark beetles under the bark of infested trees. While some trees do survive bark 

beetle attack, the vast majority are killed once infested.

To kill the beetles, cut down the infested trees and debark or burn all material greater than 4 

inches in diameter. Burying trees is another option. Bucking and splitting infested trees for firewood may kill some beetles if done in the summer and if the wood is located where it can dry out 

quickly. However, if firewood is stacked or placed in the shade before it dries, most of the beetles 

will survive. 

If infested trees or slash are not treated, removed, or burned, adult insects will emerge the following spring and attack standing trees nearby. Pinyon ips (and other ips) may emerge in as little 

as 35 days to repeat another reproductive cycle (2-4 cycles per year). In the case of spruce beetle, 

adult beetles will also emerge during the second spring. 

By the time trees have red-brown needles, most bark beetles have left the tree; however, spruce 

beetles can emerge from trees with practically no needles. Other beetles and larvae may be observed, but they are of little concern in causing further tree mortality. Most are beneficial wood decomposers – not tree killers. The tree may be cut down for firewood or left standing for wildlife 

habitat (see below). The tree should be removed, however, if it has the potential to endanger persons or property. 

Dead Trees 

are 

“Home”

to Many

Forest 

Creatures

Chipping slash

Thinned pine stand
Forest Health Protection – Intermountain West 

Chemical Treatments

PHEROMONES

• MCH for Douglas-fir beetle: MCH (one-methy-cyclo-hex-3-one) is a chemical used by 

Douglas-fir beetle to communicate (a ‘pheromone’). This pheromone tells the beetle that the 

tree is already fully occupied and they should look elsewhere for a tree to lay their eggs in. 

The chemical has been commercially synthesized and is available in small bubble caps that 

are easily stapled to tree boles just prior to beetle flight in mid-May. Application rates should 

be 30-40 bubble caps per acre for area protection or 2-4 caps per tree for individual tree 

protection. The cap slowly releases the pheromone and is generally effective for one season if properly applied. Current cost per cap is under $2. See ‘Using MCH to Protect Tees and 

Stands from Douglas-fir beetle Infestation’ at http://www.fs.fed.us/r1-r4/spf/fhp/publications/

MCH_brochure/MCH_online.pdf for more information.

• VERBENONE for mountain pine beetle: Verbenone (4,6,6-trimethylbicyclo[3.1.1]-hept-3-en2-one) is considered the principal pheromone used by mountain pine beetle to tell other beetles that the tree is fully 

occupied and to move on. As with MCH, this chemical has been commercially synthesized, however the cost is closer to $8 a pouch. Recommended dosage is 40 pouches per acre (area protection) or 2+ pouches per tree for individual tree protection; applied around mid-June. Verbenone pouches have shown mixed results 

in repelling mountain pine beetle attacks. In some previously treated sites where population 

pressures were high, the verbenone applications have had only limited success. Research 

studies in Idaho and Montana are currently being conducted to determine if population densities affect the performance of verbenone treatments. It is also critical that currently infested trees be removed from the area before the pouches are deployed or efficacy is greatly 

reduced. Generally, use of verbenone is limited to areas where insecticide application (see 

section below on Carbaryl) is not feasible.

• Contact your state forest health specialist (see page 12) for assistance to 

determine if these treatments will be effective and if financial assistance is available to help 

defray your costs.

INSECTICIDES

• Carbaryl for mountain pine beetle, Jeffrey pine beetle, spruce beetle, Douglas-fir beetle, and pinyon ips: Application of this insecticide prior to beetle flight will protect pines, 

spruces, and Douglas-fir from the beetles described in this pamphlet. However, carbaryl 

is not approved for use against fir engraver or western balsam bark beetle on true firs. Due to 

the cost and the need for special equipment, this treatment is generally used only on individual, high value trees, and is generally applied by certified applicators. All tree bole surfaces must 

be completely soaked up to a height where the tree is too small in diameter to be useful habitat. 

While labeled as being an annual treatment, research has shown that the effectiveness generally lasts 18-24+ months. Contact your state’s forest health specialist (see page 12) to determine if this is an appropriate treatment for your trees. Contact your state’s agriculture department (see page 12), division of pesticides, for assistance finding qualified applicators.

• Other insecticides for bark beetles: Other insecticides such as pyrethroids are registered for use against some bark beetles. Research has shown some success with pyrethroids but they do not last as long or work as effectively as Carbaryl. 

• Systemic treatments applied to the soil around the tree or inserted into holes drilled in 

the tree have not been shown to be effective although new injection systems and insecticides are currently being tested. 

• PESTICIDE PRECAUTIONS

Pesticides used improperly can be injurious to humans, animals, and plants. Follow directions and read all precautions on the label. Consult your local county agriculture agent 

or State extension agent about restrictions and registered uses of particular pesticides.

MCH bubble cap

Verbenone pouch

Carbaryl application
Forest Health Protection – Intermountain West

Bark beetles are small (<1/4"), hard bodied beetles that bore through the protective bark of a tree to lay their 

eggs in the moist, living tissues. These beetles and the larvae they produce feed on this living tissue, cutting 

off the tree’s ability to transport water and nutrients. The shape of the tunnels created by adult beetles and 

their larvae as they feed are unique for each species of beetle. The principle gallery is created by the female 

who lays eggs along the gallery walls (egg gallery). The eggs hatch and the larva create ‘larval galleries’ that 

tend to increase in width as the larva increases in size. (Also see the beetle-specific information on page 5.)

What is a Bark Beetle?

Mountain (and 

jeffrey) pine 

beetleS

Mountain pine beetle 

is a native to forests of 

western North America and 

attacks all species of pine 

except Jeffrey pine; Jeffrey 

pine is attacked by the 

similar Jeffrey pine beetle. 

Periodic outbreaks of these 

beetles, especially of mountain pine beetle, can 

result in the loss of millions of trees. 

During low population levels, attacks are 

primarily on trees under stress from injury, poor 

site conditions, overcrowding, root disease, or 

old age. As the beetle populations increase, attacks may involve most trees 8 inches in diameter or greater in the outbreak area, regardless of 

their apparent health. 

Adults are brown to black in color and about 

3/16 inch long with a rounded back end. The larvae are yellowish white, legless grubs with dark 

heads, found within tunnels under the bark.

Successfully attacked trees normally do not 

show red, faded foliage until 8 to 10 months after attacked. However, 

drought stress will cause 

some trees to start “fading” as early as 4 to 5 

months after attack.

Mountain pine beetle adults leave the dead, 

yellow- to red-needled 

trees and attack green 

trees from July through 

September with the majority flying in mid to 

late July.

The female mountain pine and Jeffrey pine 

beetles create straight, 

vertical (with grain of 

wood) egg galleries that 

can extend up to 3 feet in length or more. At the 

bottom of this gallery where the attack was initiated is a distinctive J-shaped crook. Eggs are 

laid alternately along the walls of the egg gallery.

Douglas-fir beetle

This beetle is a native to forests of western North America and only attacks Douglasfir trees. Outbreaks typically occur in areas of 

wind-thrown trees or trees damaged by fire or 

spruce budworm defoliation. The Douglas-fir 

beetle generally does 

not cause widespread 

mortality like mountain 

pine beetle. Groups of 

trees ranging from a 

few to several hundred 

trees may be killed. Although large outbreaks 

sometimes occur due to 

drought stress and dense stand conditions.

The Douglas-fir beetle prefers large trees, 

but will attack trees as small as 6 inches in diameter. Depending on weather and elevation, attacks occur from late April through August, with 

peak flights occurring from early June to early July.

While physiologically dead within a few 

weeks, trees 

typically do 

not show yellow-green 

(“fading”) or 

red foliage until 10 months 

or more after 

being attacked. 

With trees that 

are drought 

stressed, “fading” may occur by the fall 

following the attack (4 to 5 months).

Adult beetles are brown to black in color and about 3/16-inch long. The larvae are 

whitish, legless grubs with brown heads found 

within tunnels under the bark. Eggs are laid in 

groups on alternative sides of the female’s gallery, creating a unique pattern. The female’s gallery may be 8x10 inches long starting at the bottom with a small angled ‘J’.

Spruce Beetle

This beetle is a native to forests of western 

North America and attacks all species of spruce, 

although Engelmann is preferred; blue spruce 

is seldom attacked. Outbreaks typically begin 

in areas of wind-thrown trees, then move into 

standing trees. In landscapes dominated by Engelmann spruce, extensive mortality can occur. 

Adult beetles are 1⁄4 inch long, brown to 

black in color with reddish-brown or black wing 

covers. The larvae are yellowish white, legless 

grubs found within tunnels under the bark.

Unlike the previous two bark beetles, spruce 

beetle can have a one- or two-year life cycle. Infested trees usually do not “fade” (turn yellowgreen or reddish) until one or sometimes 

two years after attack. 

The spruce beetle 

egg galleries average 

3-12 inches in length 

with a slight 

crook at the start. 

Eggs are laid alternately along 

the gallery with 

larva feeding 

gregariously outward in all directions. 

DOuglas-fir 

beetle

Douglas-fir beetle 

galleries

Feeding larvae 

girdling tree

spruce beetle

Spruce beetle gallery

mountain

pine beetle

Mountain

pine beetle

galleries
Forest Health Protection – Intermountain West

OTHER AGENTS . . .

that cause damage similar 

to that of bark beetles

Other insects or animals can cause damage to trees that may resemble bark beetle activity. We have listed a few of these to 

help you discern between bark beetles and 

activity from other agents. 

OTHER WOOD DAMAGING 

AGENTS:

Because bark beetles have often left 

the tree by the time you see red needles, 

your inspection of a dead tree may find insects that were not directly responsible for 

the tree’s death. Many of these insects live 

under the 

bark of 

dead and 

dying trees 

and are important in 

recycling 

the nutrients back 

into the 

ground. 

Most 

often confused with bark beetles are the metallic and 

longhorn wood borers. Wood borers are much larger than bark beetles. These 

borers feed on the phloem just as bark beetles do; however, their galleries lack a distinct shape. While developing, the larva may 

drill large oval or round holes into the wood. 

Their life cycle may take from one to over 

10 years to complete.

PINYON IPS

Most native bark beetles in the ‘ips’ group 

are not very aggressive tree killers. Rather 

they tend to rely on recently dead, damaged or 

stressed trees for 

food and reproduction. Pinyon ips, a 

native ips, is no exception. However, their host trees 

are often found in 

areas prone to water and heat stress (droughts) which makes them 

susceptible to attack. During drought periods, 

pinyon ips is able to overcome the weakened defenses of trees, affecting broad landscapes. Because this beetle can have two or more generations in a year it is able to spread quite rapidly 

when conditions are favorable.

Attacks begin early in the spring, and attacks can continue through early fall.

Pinyon 

ips are about 

1/5 inch long, 

and have a 

spiny back 

end typical of 

all “ips’ species (versus a 

rounded back 

end). Gallery 

patterns of 

most ips are 

similar; often a Y or H 

shape, with a 

larger ‘mating’ gallery from which the separate 

egg galleries radiate. Larva and beetles overwinter under the bark, consuming large patches of 

inner bark and lacking specific galleries. Wood 

borers (see side panel) are quick to infest attacked trees after pinyon ips have attacked.

fir ENGRAVER

Also a native bark beetle, this species attacks true firs. It does not attack Douglas-fir 

which is not a true fir. 

Measuring only about 1/8 inch, these small, 

shiny, black 

beetles are distinguished by 

having a truncated, spineless, 

back end. The 

gallery pattern 

is also unusual 

in that the egg 

gallery runs 

across the 

grain of the 

wood (horizontally) for 

4 to 12 inches with the 

larval galleries extending up and 

down with 

the wood grain. Shortly after attack, a fungus 

that travels with the beetle starts to stain the area 

a yellow-brown color.

The larva overwinter under the bark with 

the adult beetles emerging around June, and dispersing from June through September. Most 

populations have a one-year life cycle, occasionally two years at higher elevations. Larva and 

pupae are similar to those of other bark beetles.

WESTERN BALSAM 

BARK BEETLE

Only about 1/8th to 1/6th of an inch long, a 

magnifying glass may be needed to see the distinctive hairy patch (toupee) on the head of this 

beetle. The gallery pattern is star shaped, and 

often accompanied by a lesion caused by fungi 

that assist in killing 

the tree. 

The beetle is the 

most conspicuous 

agent in a complex 

that is responsible for killing large 

numbers of subalpine fir throughout the Intermountain West. Other agents in the 

complex include root disease and balsam woolly adelgid. 

In addition 

to drought, 

windthrow 

has been 

known to 

initiate 

large scale 

outbreaks 

of this insect.

Western balsam bark beetle normally needs 

two years to develop. However, a one year life 

cycle is possible under the right weather conditions. Two peak flights of this beetle occur in 

late June/ early July and again in late July / early August.

Metallic wood borer

Longhorn wood borer

A bark beetle (left) and 

wood borer (right)

pinyon ips

Typical ips gallery

fir engraver

fir engraver GALLERY

Western balsam 

bark beetle

Western balsam bark 

beetle gallery
10 Forest Health Protection – Intermountain West

DEFOLIATING INSECTS:

Other insects and diseases can cause damage to the needles of trees by either consuming 

the needles or causing the trees to drop their 

needles. The ‘defoliating’ agents can cause 

trees to die if they remove most of the needles 

over a several year period. Most conspicuous 

are several moth larvae that eat foliage, especially the western spruce budworm and the 

Douglas-fir tussock moth.

Western spruce budworm

HOSTS: Douglas-fir, all true firs, spruce, and 

larch.

Western spruce budworm is a small moth. 

In the caterpillar stage, it feeds on the needles 

of trees. Populations of this defoliating insect 

periodically rise to outbreak levels. 

The weather naturally regulates this insect’s population. During recent years, drought 

conditions have left trees severely water 

stressed and susceptible to insect infestations. 

Budworms grow more vigorously in stressed 

trees. If drought conditions continue, budworm populations can increase dramatically where there is an abundance of susceptible 

tree species. Forested stands, which are densely stocked with predominantly Douglas-fir or 

subalpine fir and are multi-storied, are at high 

risk to infestation. 

Tree damage is caused by the budworm 

caterpillars (larvae) feeding on needles in the 

early spring through summer. Larvae primarily consume current-year foliage, but can move 

to older needles in extreme cases. Infested 

trees will appear to have a red luster when observed from a distance. Upon closer inspection, branch tips will be bare or covered with 

nests of silk webbing and dead needles. Several years of 

continued defoliation will 

reduce tree 

growth and 

Ambrosia

beetleS are 

very small, creating 

multiple pin holes 

in wood where they 

cultivate a fungi (ambrosia) that 

they feed on.

development, and 

sometimes cause 

death. In addition, 

budworm defoliation 

stresses the trees and 

makes them more 

susceptible to bark 

beetle attack. 

Western spruce 

budworm populations can be reduced with insecticides. If you feel spraying is needed, contact 

your local 

State Forester (see page 

12) for treatment recommendations. 

You may 

also contact 

a licensed, 

professional 

pesticide applicator. Promoting non-host species 

such as aspen or pines will reduce overall stand 

susceptibility.

Douglas-fir Tussock Moth

HOSTS: Douglas-fir, all true firs, and spruce.

Feeding damage and light webbing from 

Douglas-fir tussock moth is similar to that of 

western spruce budworm, but the larva, egg 

masses, and cocoons are distinctly different. 

Most identifiable are the oldest larva which have 

four dense patches of yellowish brown hair (tussocks) and two hair ‘horns’ at the back and two 

at the front. Younger larva lack these long ‘horn’ 

tufts but will have the four tussocks. The youngest larva are a plain gray with long hairs. The 

adult male is a non-descript brown moth. The female does not have wings and is usually found 

near her cocoon.

In the fall, females lay egg masses in a gelatinous substance and attached to foliage, twigs, 

trunks, under limbs, or other objects near the 

tree. These eggs hatch in the spring when the 

buds on their host trees start to open. The early 

larva feed on this new foliage, often stringing a 

loose webbing 

from branch to 

branch. In late 

July-early August the larvae pupate and 

the new moths 

emerge about 

two weeks later to mate and 

start the process over.

The most 

visible defoliation occurs in 

the later larval stages in July. Mature, dense 

stands with trees of different ages, especially in dry sites, are most often affected. High 

population levels (outbreaks) can last for 2-3 

years; long enough to kill entire stands of host 

trees. Top kill and some tree mortality can 

occur in only one year of heavy defoliation. 

Non-fatal defoliation or continual low-level 

defoliation can also cause decreased growth 

and vigor, often making the trees more susceptible to bark beetle attacks (e.g. Douglasfir beetle, spruce beetle, and fir engraver).

Even woodpeckers (sapsuckers) 

can make holes 

in the bark that 

may look like a 

bark beetle entrance/exit hole.

Wood

wasp larva 

make large 

holes in dead 

wood similar 

to wood borers but the larva do not 

feed in the phloem.

Tree crown damage 

from feeding larvae

Feeding larvae

Western spruce budworm 

adult and pupal case

Douglas-fir tussock 

moth damage to twigs 

and over landscape

Douglas-fir tussock moth male and 

female; early stage larva; late stage 

larva with ‘tussocks”
Forest Health Protection – Intermountain West 11

Federal and State 

Land Managers

Effective management of bark beetle populations is a difficult challenge. Federal and State 

land managers know a great deal regarding characteristics that make stands susceptible to bark 

beetles and defoliators. Unfortunately, having 

this knowledge does not mean that they are able 

to prevent outbreaks. 

The most effective way of dealing with 

bark beetle outbreaks over large, forested areas is through preventative vegetation management practices. Treating vast areas such as entire 

National Forests with chemicals to reduce bark 

beetle populations is not practical or feasible. 

Land management planning is a required 

process for all Federal and State administered 

lands. Public involvement is a required – and 

encouraged – part of Federal planning efforts. 

During the Federal planning process, some areas 

are excluded from vegetation management (i.e. 

wilderness areas, roadless areas). Within these 

areas, treatments to manage an insect outbreak 

are often not available.

Where vegetation management activities are 

permitted, Federal and State land managers can 

reduce insect-related tree mortality. Examples 

of management activities that can reduce forest 

susceptibility to insect damage include: 

➤ Remove some of the trees in dense stands 

through thinning to improve tree vigor and 

reduce susceptibility to bark beetles. 

➤ Promote a diversity of tree species, which 

also reduces stand susceptibility to bark beetles.

➤ Promote a diversity of age classes (not always recommended for defoliators). 

➤ Remove small pockets of bark beetle infested trees when they first appear in an area. 

This can be an effective way of suppressing 

populations. This method may not be effective in eliminating all beetles in an area if infested trees remain in susceptible sites. 

Recent changes through the Healthy Forests Restoration Act of 2003 and the President’s 

Healthy Forests Initiative, have given Federal 

land managers tools that will reduce delays and 

statutory barriers for projects which target improving forest health and reducing hazardous fuels. Federal land managers have used these tools 

to expedite projects aimed at reducing insect related mortality and thus decreasing hazardous 

fuels for wild fires.

Challenges of a Bark Beetle Outbreak – 

What are Land Managers Doing?

Private Landowners

Each private landowner has different objectives for their property and trees. Each will have 

their own opinion about possible management 

techniques. Some will choose to do nothing; 

others will adopt aggressive bark beetle suppression strategies. 

A neighbor who chooses not to remove beetle-infested trees will increase the probability 

that susceptible trees on adjacent property could 

be attacked. Obviously, these situations can become complicated. Tree removal options are not 

equally available to all landowners. Economics 

of the treatment may be a factor, especially for 

large properties. Site conditions, such as steep 

slopes, may make tree removal difficult. 

Fortunately, using MCH caps for Douglasfir beetle or Carbaryl insecticide for mountain 

pine beetle, Jeffrey pine beetle, spruce beetle, 

and pinyon ips, can be effective, preventative 

treatments for trees on your property; irregardless of what your neighbor chooses to do. However, treatments need to continue until the outbreak in your area collapses.
34.08.400.09/06

12 Forest Health Protection – Intermountain West

Where to go for help or 

additional information

ORGANIZATIONS

■ For on-the-ground technical assistance with insect and forest management 

on private lands:

- In Idaho, contact Jeff Fidgen, Idaho Department of Lands, (208) 666-8624, 

jfidgen@idl.idaho.gov, (http://www.idl.idaho.gov/Bureau/forasst.htm)

- In Montana, contact Amy Kearney, Montana Department of Natural 

Resources, (406) 542-4283, (http://dnrc.mt.gov/forestry/assistance/pests/

default.asp)

- In Nevada, contact Gail Durham, Nevada Division of Forestry, (775) 684-

2513 or 687-0431, gdurham@forestry.nv.gov, (http://agri.nv.gov/PLANT_

Entomology_index.htm)

- In North Dakota, contact Michael Kangas, North Dakota Forest Service, 

(701) 231-5936, Michael.Kangas@ndsu.nodak.edu

- In Utah, contact Colleen Keyes, Department of Natural Resources Division 

of Forestry, Fire, and State Lands, (801) 538-5211, ColleenKeyes@utah.gov

- In Wyoming, contact Les Koch, Wyoming State Forestry Division, (307) 

777-5495, lkoch@state.wy.us

■ For information on professional pesticide applicators and insecticide 

registration contact your local state Department of Agriculture, division of 

pesticide licensing. Web pages to assist you with the contacts are listed 

below:

- Idaho: http://www.agri.idaho.gov (see noxious weed contacts)

- Utah: http://ag.utah.gov/

- Wyoming: http://wyagric.state.wy.us/techserv/tsindex.html

- Montana: http://www.agr.state.mt.us/ (see pesticides, program contacts)

- Nevada: http://agri.nv.gov/index_Plant2.htm or http://agri.nv.gov/PLANT_

Chemistry_Index.htm

- North Dakota: http://www.agdepartment.com/Programs/Plant/Pesticides.

html (see laws and regulations for contacts)

■ For general National Forest information, contact the National Forest directly

■ For information on USDA FS Forest Health Protection for the Northern and 

Intermountain Region, visit http://www.fs.fed.us/r1-r4/spf/fhp/index.html

■ Visit the FIREWISETM program at www.firewise.org

■ Additional pictures of the various trees and insects mentioned in this 

pamphlet can be found at www.bugwood.com

PUBLICATIONS

■ A Field Guide to Diseases and Insect Pests of Northern & Central Rocky 

Mountain Conifers (http://www.fs.fed.us/r1-r4/spf/fhp/field_guide/index.htm)

■ Forest Insect and Disease Management Guide (http://www.fs.fed.us/r1-r4/

spf/fhp/mgt_guide/index.htm)

■ Forest Insect and Disease Leaflets (FIDLs) are available for a variety of 

forest pests (http://www.na.fs.fed.us/spfo/pubs/fidl.htm)

■ Using MCH to protect trees and stands from Douglas-fir beetle infestation 

(http://www.fs.fed.us/r1-r4/spf/fhp/publications/MCH_brochure/MCH_online.

pdf)

The Role

of Fire

Dead trees with red needles, whether killed by bark beetles or other agents, 

are more flammable than live trees. However, once the needles are gone, the standing dead trees generally do not pose an 

increased risk of wildfire. As the trees eventually fall to the ground, increasing downed 

fuel loads have the potential to again increase fire severity.

Fire is a fundamental part of the natural ecosystem. The vegetation in the Intermountain West has evolved with fire and, 

in many cases, relies on fire to sustain its 

health and its presence on the landscape. 

However, fire around your home or other infrastructure is usually not desirable. 

Research has shown that the most critical factors for a home surviving a wildfire 

are the construction of the home and the 

vegetation near the home.

FIREWISETM is a multi-agency, nonprofit program devoted to helping people 

and their property survive a wildfire. The 

program encourages developing a “defensible space” around your home. Information 

on how to improve the survivability of your 

home from wildfire can be found on a variety of FIREWISETM websites. 

Some general recommendations are:

1. Roofs should be made of non-flammable material.

2. Enclose places where fire embers could 

accumulate such as soffits and underneath porches. 

3. Thin out dense trees or shrubs.

4. Remove brush or dried grasses close to 

your home.

5. Landscape with fire resistant plants.

6. Do not place flammable material such 

as firewood or above ground propane 

tanks near your home.

Firefighter safety is a primary consideration in any fire incident. Creating a “defensible space” will increase the chance that 

firefighters can safely protect your home.

For more information regarding

protecting your home from

wildfire, visit the FIREWISETM

website (see box at left) or

contact your local fire department.

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.