► R5-PR-033

► February 2015

Native bark beetles cause high levels of 

tree mortality in California. When, where, 

and the extent to which mortality occurs is 

primarily influenced by forest stand and drought 

conditions. A dramatic rise in the number of dead 

trees follows one to several years of inadequate 

precipitation. The more severe and prolonged 

the drought, the greater number of dead trees. 

Dense groups of trees are particularly susceptible 

to bark beetle attacks due to stress caused by 

competition for limited resources. Stressed trees 

equate to suitable host material for bark beetles 

and successful reproduction results in more 

beetles and higher levels of tree mortality.

Tree mortality caused by bark beetles can 

rise sharply in a short amount of time, similar 

to that observed in the southern part of the state 

in 2003. The primary reason for increases in 

tree mortality have been periods of severe and 

protracted drought combined with high tree 

densities. High levels of tree mortality will occur 

if forests are not altered to improve tree health 

and resilience.

The bark beetles causing widespread 

mortality in the forests and forested communities 

in California are all native. The principal species 

include: mountain pine beetle, fir engraver beetle, 

western pine beetle, Jeffrey pine beetle and pine 

engraver beetles.

What is a bark beetle?............................page 2 

What causes similar attacks? ...........page 4 

Are my trees susceptible? .................page 5

Have my trees been attacked?.........page 8

How to prevent attacks........................page 9

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

Who should I contact? ...........................page 12

Does this affect you? 

Look inside!

Bark Beetles in California Conifers

Are Your Trees Susceptible?

Individual bark beetles are not much larger 

than a piece of cooked rice. Not only are they 

small and difficult to see, their activity is often 

scattered and hardly noticeable.

Bark beetles survive in trees that are stressed, 

diseased, or injured; either by human activity or 

during storms or wildfires. Occasionally, small 

groups of standing trees may be killed but over 

the landscape they are often unnoticed.

Bark beetles can increase dramatically when 

sufficient food is available. Typically this is in 

the form of drought-stressed trees. High numbers 

of these small beetles (outbreak populations) 

attack trees en mass. Often many trees are killed 

over the landscape; likened to that of wildfire. In 

many years, more trees are 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 “pitchout” 

the beetles that attempt to enter. When trees are 

stressed they may be unable to produce sufficient 

amounts of defensive pitch. When beetle 

populations are high, even an apparently healthy 

tree may not be able to produce enough pitch to 

ward off hundreds of attacks (a mass attack). In 

addition, many beetles carry fungi that further 

impair the tree’s defense system.

How can something 

so small kill 

something so big?

This publication was developed to educate the public regarding the principle tree-killing bark beetles in California. 

With this knowledge, you can make informed decisions concerning improving tree health on your private property 

and provide meaningful input about proposed actions on public lands.

Federal and State Forest Health Staff are available to assist you with additional information. Please see page 12 

for a list of contacts and additional information sources.

Widespread tree mortality near 

Idyllwild, CA - 2003

Successful 

attack

trees killed by bark beetles

unsuccessful 

attack

PITCH TUBES

( ) ( )
2 Forest Health Protection – California

Bark beetles are small (< 1⁄4 inch), hard bodied beetles that bore through the protective bark of a tree to lay their eggs in the moist phloem (inner bark). 

These beetles and the larvae they produce feed on this living tissue, cutting off the tree’s ability to transport nutrients. The gallery pattern on the 

underside of the bark created by adult beetles and their larvae as they feed are unique for each species of beetle. The parent gallery is typically created 

by the adult female beetle who deposits eggs along the gallery walls. The eggs hatch and the larvae create ‘larval galleries’ that tend to increase in 

width as the larvae increase in size.

What is a Bark Beetle?

Mountain Pine Beetle

The mountain pine beetle is native to 

forests of western North America and attacks 

ponderosa, lodgepole, sugar and other species 

of pine. It does not 

attack Jeffrey pine. 

Periodic outbreaks 

of mountain pine 

beetles can kill 

millions of trees. 

D u r i n g 

low population 

levels, attacks are 

primarily on trees 

stressed by injury, 

poor site conditions, 

o v e r c r o w d i n g , 

root disease, 

or old age. As 

beetle populations 

increase, attacks 

may involve most 

trees 6 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. 

Larvae are yellowish-white, 

legless grubs with dark heads, 

found within galleries under 

the bark.

Attacking beetles release 

chemicals called aggregating 

pheromones that attract other 

beetles until a mass attack 

overcomes the tree. Attacks 

may “spill over” into adjacent 

trees causing what is known as a “group kill”. 

Crown fade on successfully attacked trees 

typically occurs within 4 to 10 months. Droughtstressed trees may fade in a shorter period of 

time.

Mountain pine beetle adults fly from May 

through October, depending on temperature. 

Beetles usually take one year to complete their 

life cycle; at higher elevations 2 years may be 

required and at lower elevations two generations 

may occur in one year.

Female mountain pine beetles create 

straight, vertical (with grain of wood) galleries 

that can extend up to 3 feet or more in length. 

Eggs are laid alternately along the sides of the 

gallery. Larvae feed on phloem, constructing 

galleries at right angles to the parent galleries. 

The combination of beetle attacks, gallery 

construction and feeding, and staining fungi, 

cause the tree to die.

Western Pine Beetle

This beetle is also native to western North 

American forests and primarily attacks ponderosa 

and Coulter pines in California. During drought 

periods it can kill trees of all ages and vigor 

classes. Group killing of trees is common. 

Adult beetles are dark brown and about 1⁄4 

inch long. Larvae are small, white, legless grubs. 

Western pine beetle larvae mine a short gallery in 

the phloem and then turn into the middle bark to 

complete their development.

Attacking beetles release chemicals called 

aggregating pheromones that attract other beetles 

until a mass attack overcomes the tree. Attacks 

may “spill over” into adjacent trees causing 

what is know as a “group kill.” Western pine 

beetles typically fly from late spring through late 

October. One to three generations may occur in 

a single year.

The adult gallery pattern of the western 

pine beetle is winding and crisscosses in several 

directions. It is the only bark beetle that makes this 

particular type of gallery. Galleries are usually 

tightly packed with frass. Flaking of the bark by 

woodpeckers in search of beetle larvae exposes 

the bright-orange colored inner bark, making 

infested trees quite apparent. The combination of 

beetle attacks, gallery construction and feeding, 

and staining fungi, cause the tree to die.

Jeffrey Pine Beetle

Jeffrey pine beetle is the principal insect 

enemy of Jeffrey pines. This native beetle occurs 

throughout most of the range of Jeffrey pine, and 

similar to the mountain and western pine beetle, 

it can cause high levels of tree mortality. Adult 

beetles are reddish-black and about 5/16 inch in 

length. Larvae are curved in shape, mostly white, 

and have yellowish colored heads. 

Similar to the two previously discussed bark 

beetles, Jeffrey pine beetles attack trees by boring 

through the outer bark and into the phloem. Adult 

galleries run vertical with the grain of the wood 

and larval galleries extend at right angles acoss 

PITH

XYLEM

CORK 

CAMBIUM

CAMBIUM

BARK

PHLOEM

Galleries constructed by 

western pine beetles.

mountain pine beetle 

gallery and life 

stages
Forest Health Protection – California 3

the grain. No other insect that breeds in Jeffrey 

pine makes galleries like these. Adult galleries 

may have a characteristic “J” shape and are 

packed with frass. These bark beetles also use 

pheromones to communicate and also carry 

staining fungi. Jeffrey pine beetles typically 

take a year to complete one generation but two 

generations per year may occur depending on 

temperature.

Once a group kill occurs in an area, emerging 

beetles tend to attack the next closest green trees, 

so group kills continue to enlarge every year until 

the infestation collaspes. High levels of Jeffrey 

pine mortality have been observed over the past 

several years; primarily corresponding with 

drought. Large diameter trees may initially be 

favored, however, if beetle populations are high 

enough, trees as small as 3 inches in diameter 

may be attacked and killed.

RED TURPENTINE 

BEETLE

The red turpentine beetle is the largest of the 

pine bark beetles in California. It usually attacks 

trees with poor vigor, those infested by other 

bark beetles, mechanical or fire-injured trees or 

those that have injured or poor root systems. It 

also commonly attacks the stumps of freshly cut 

trees, but does not typically attack green slash. 

Adult beetles are about 1⁄4 inch in size and reddish 

brown. Peak flight activity and attacks usually 

occur in the spring. Most attacks are on the lower 

bole near ground line but they can also be higher. 

Pitch tubes vary in size, texture, and color, 

depending on the host tree and can be as large as 

2 inches across. Eggs are laid in a mass along the 

side of the parent gallery. Larvae feed together 

into fresh tissue; their feeding kills a patch (may 

vary in size from a few to several inches wide) 

of inner bark (phloem). Galleries can extend 

below the ground surface into the roots. In 

most areas there is at least one generation per 

year. Successful red turpentine beetle attacks 

alone may not kill trees, however they typically 

indicate that the tree is stressed or injured, and 

their attacks may predispose trees to attack by 

other bark beetles. As with most bark beetle 

species, maintaining tree health and minimizing 

tree injuries will reduce the likelihood of attacks.

PINYON IPS

Most native pine engraver beetles in the ‘ips’ 

group are not very aggressive tree killers. Rather 

they tend to rely on injured or stressed trees or 

green slash 

for food and 

reproduction 

sites. Pinyon 

ips, a native 

ips, is no 

e x c e p t i o n . 

Host trees 

are often found in 

areas prone to droughts which increases tree 

susceptibility to attack. During drought periods, 

pinyon ips are able to overcome weakened 

defenses and kill high numbers of trees across 

broad landscapes. This beetle can have two or 

more generations per year with attacks beginning 

early in the spring and continuing 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. Larvae and 

adults overwinter under the bark and consume 

large patches of inner bark.

There are 

several other 

native pine 

engraver beetles 

that infest pines 

and green pine 

slash. They 

can cause top 

kill or whole 

tree mortality. 

Adults have 

various numbers 

of spines on 

the back end 

depending on the species. Number of generations 

per year varies by species and temperature.

FIR ENGRAVER 

BEETLE

Also a native bark beetle, this species attacks 

true firs. It does not attack Douglas-fir (not a true 

fir).

About 1/8 inch in length, these small, shiny, 

black beetles are distinguished by having a 

truncated, spineless, back end. The parent gallery 

cuts across the grain of the wood (horizontally) 

for 4 to 12 inches and the larval galleries extend 

up and down with the wood grain. Shortly after 

attack (no pitch tubes), a fungus carried into 

the tree by 

the beetles 

starts to 

stain the area 

a yellowbrown color.

L a r v a e 

overwinter 

under the bark and adult beetles emerge from 

June through August. There is typically one 

generation per year. Larvae and pupae are similar 

to those of other bark beetles.

Douglas-fir Beetle

This beetle is a native to forests of western 

North America and only attacks Douglas-fir 

trees. Outbreaks in California typically occur in 

areas of wind-thrown trees. 

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 

galleries under the bark. Eggs are laid in groups 

on alternative sides of the parent gallery, creating 

a unique pattern.

pinyon ips

Typical ips gallery

fir engraver

Red turpentine beetle pitch tubes

fir engraver beetle 

gallery

Douglas-fir beetle 

galleries
OTHER AGENTS . . .

that attack trees

Other insects or animals can cause injuries to trees that may resemble bark beetle activity. Listed below 

are a few of these to help you discern between bark beetles and other 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 nutrients. 

Most often confused with bark beetles are the metallic and longhorned WOOD BORERS. Wood borers 

are much larger than bark beetles. Wood borers can feed on the phloem, sapwood and into the heartwood. 

Larvae may drill large oval or round holes into the wood. Their life cycle may take from one to several years 

to complete.

A bark beetle (left) and 

wood borer (right)

sculptured wood boreR

Ambrosia beetle 

and galleries

Wood wasp ovipositing 

in wood

Wood borer

larva

Tree injury caused by 

sapsucker feeding

Sapsucker drilling 

tree for sap

longhorned 

wood borer

4 Forest Health Protection – California

AMBROSIA BEETLES

are very small and create 

multiple pin holes in wood 

where they cultivate a 

fungi (ambrosia) to feed 

on. White boring dust 

in bark crevices and in 

webbing on the bark 

surface is easily visible.

Woodpeckers 

(SAPSUCKERS) can 

make holes in the bark 

that may look like a bark 

beetle entrance/exit hole.

WOOD WASP larvae 

make large holes in dead 

wood similar to wood 

borers but larvae do not 

feed in the phloem.

Wood borer 

larvae
Forest Health Protection – California 5

Ponderosa Pine

Ponderosa needles are 2-3 to a bundle, ranging from 

3-10 inches in length. Cones are 3-5 inches long and 

armed with small spines.

Range in California: Widespread in the lower and 

middle elevation forests throughout the State.

Jeffrey Pine

Very similar to ponderosa pine. Needles are in bundles 

of 3, occasionally 2. Cones are larger and stouter (5-9 inches) and have 

incurved spines (prickly ponderosa; gentle Jeffrey).

Range in California: Dominates on serpentine throughout the Klamath 

Mountains and north Coast ranges. 

In the southern Cascade and Sierra 

Nevada ranges it is found in the mixed 

conifer forest. It is the dominant pine 

on much of the eastside of the Sierra 

Nevada from Lake Tahoe south and 

commonly mixes with ponderosa pine. 

It occurs with Coulter pine and replaces 

ponderosa pine in the interior forests in 

southern CA.

Lodgepole Pine

Needles are two per bundle; 1-3 inches 

long. The small 3⁄4-2 inch long cones have 

very short stalks and stay attached to the 

tree for many years. Cones are prickly.

Range in California: Scattered 

distribution along the coast (shore 

pine). Found in the southern Cascade 

and Sierra Nevada ranges and in the 

Step 1: Identify Your Trees

The first step in determining if your tree is susceptible to attack by bark beetles is to know what species of tree you have. The principal conifers found in 

forested communities in California are highlighted below.

Are Your Trees Susceptible to Attack by Bark Beetles

What Should You Do?

San Bernardino, San Jacinto and San 

Garbriel mountains in southern CA. 

Often found in wet areas or in frost 

pockets.

Sugar Pine

Five-needle bundles. Cones are 10-18 

inches long. Upper branches on large trees 

are often sprawling and turned upward.

Range in California: Klamath mountains and north coast ranges, Cascade 

and Sierra Nevada ranges, and at higher elevations in southern California.

Pinyon Pine

Singleleaf pinyon: Needles are single, slighty 

curved and sharp tipped, 1-2 inches long and 

are green-gray. Cones are reddish-brown 

and 2-3 inches long. Cones can remain on 

the trees for many years. Trees are up to 40 

feet tall, may be multi-stemmed at the base 

and branches can be low on the bole near 

the ground. Parry pine: similar in general 

appearance, however needles are in bunches 

of 4.

PINES: 

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

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

ponderosa pine cone

ponderosa pine

jeffrey pine cone

lodgepole pine 

needles

lodgepole pine cones

pinyon pine cone

sugar pine tree

sugar pine cone
Needles on fir trees are not in bundles but are attached 

individually to the stem; the shape of the needle can differ by tree species.

Trees in this family have small, scale-like leaves that are 

usually pressed against the branchlet. 

Incense Cedar

Scale-like leaves that are opposite each other, 

overlapping and closely pressed against the 

branchlets. Leaves are oblong to egg-shaped 

and are sharply pointed at the tip. Cones 

are small, yellow to yellowish-green, and 

hang downward. Range in California: Very 

common species over a broad elevation range 

in the Sierra Nevada. Tends to be restricted 

to serpentine soils in the north Coast Ranges 

and western portion of the Klamath Ranges. 

In southern CA it is scattered throughout the 

mixed conifer forests.

6 Forest Health Protection – California

Pines:

White Fir

The single, flat needles narrow to a stalk at 

their base. The needles tend to be longer (2-3 

inches) and flattened on the lower branches 

and shorter (<2 inches) and curved upward 

near the top of the tree. The greenish-yellow 

cones (3-5 inches), are on the upper branches 

and point upward.

Range in California: Common and often 

dominant in higher elevation mixed-conifer 

forests. Mixes with pine on the east slope of 

the Sierra Nevada and at lower elevations.

Douglas-fir

Although not a true fir, Douglas-firs are 

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

single, flat needles. Needles are narrow at 

their base, similar to white fir. Douglas-fir 

needles are yellow-green and cones are about 

3 inches long. The cones have distinct bracts 

cOULTER Pine

Needles occur in bundles of three and cluster toward the end of the branches, giving a tuffed appearance.

Cones are 10-14 inches long and have flat, incurved, claw-like spines.

Range in California: Prominent in the southern California mixed-conifer forests. Commonly overlaps with 

Jeffrey pine.

References:

Elias, T. 1989. Grolier’s Field guide to North American trees. Grolier 

Book Clubs. Danbury, CT.

Griffin, J.R. and W.B. Critchfield. 1972.The distribution of forest 

trees in California. Pacific Southwest Forest and Range Experiment Station Research Paper 82. U.S.D.A. Forest Service.

that resemble 

the tail of 

a mouse. 

Range in 

California: 

Douglas-fir 

occurs in 

e x t e n s i v e 

stands in 

the Coast and 

Klamath Ranges and primarily on the west 

side of the Sierra Nevada Range.

Red Fir

Needles are 4-sided and are somewhat 

flattened on the lower branches, they greatly 

curve upward on the upper branches. The 

cones (2-4 inches long) are purplish to yellow 

and are upright on the upper branches.

Range in California: Dominates in the high 

elevation forests in the northern ranges and 

in Cascade and Sierra Nevada ranges. Absent 

in the Warner Mountains and in southern CA.

pINES ARE 

TYPICALLY 

MORE 

DROUGHT 

TOLERANT 

AND LESS 

SHADE 

TOLERANT 

THAN FIRS.

pLANT 

TREES 

THAT ARE 

NATIVE 

TO YOUR 

AREA.

CYPRESS: 

Firs: 

Coulter pine cone

white fir 

needles

Douglas-fir foliage 

upright 

cones stay 

on branches

red fir cones

red fir needles

incense 

cedar 

foliage
Forest Health Protection – California 7

Step 2:

Determine Your 

Trees’ Susceptibility

Susceptibility is the condition of an individual 

tree or stand of trees that predisposes it to attack 

by bark beetles.

INDIVIDUAL TREE SUSCEPTIBILITY

Stressed trees are not able to fend off bark 

beetle attacks. Tree stress can result from human 

activity (construction, paving, excavating, etc.), 

natural causes (DROUGHT, wind, lightning, 

other insect or disease agents, etc.) or from 

competition from other trees. The more stressed 

the tree, the more susceptible it may be. Poor 

crown condition is often indicative of stress. 

Susceptible trees are not always attacked by bark 

beetles, especially if beetle numbers are low. 

Conversely, it is possible when beetle populations 

are high, that even 

apparently healthy 

trees may be 

attacked. In a forested 

community, or on 

your own property, an 

individual tree may 

be of high importance 

for aesthetic or other 

values. Several types 

of treatments may be 

warranted to improve 

its health and vigor 

and protect it from 

successful attacks 

by bark beetles.

STAND SUSCEPTIBILITY

A large group of trees, or stand in its entirety, 

can also be susceptible to bark beetles. Species 

composition, tree ages, tree density, being in a 

drought prone area, having root diseases, or other 

attributes can make one stand more susceptible 

compared to another. Widely spaced trees are 

typically less susceptible to successful attack by 

bark beetles compared to densely growing trees. 

Less competition for water, light, and nutrients 

facilitates tree growth and vigor, both of which 

are important in the defense against bark beetles. 

Stands with a higher diversity of tree ages and 

tree species are also typically less impacted, as 

most bark beetles have only one or a few hosts 

and they generally are particular about the size 

of trees they attack. Mortality of one tree or 

a few trees in a stand may be quite acceptable 

depending on the management objectives for the 

area.

BARK BEETLES 

and THEIR HOSTS 

Tree-killing bark 

beetles often have a 

preference for specific tree 

species. In some cases, a 

single beetle species will 

attack only one tree type. In other cases a single 

beetle species may infest a number of similar tree 

species.

Lodgepole, ponderosa, and sugar pine: These 

native pines are attacked by mountain pine beetles. 

Ponderosa pines are also attacked by western 

pine beetles, as are Coulter pines. Jeffrey pine

is attacked by Jeffrey pine beetles. These bark 

beetles are all very similar in appearance and 

successful attacks almost always result in tree 

mortality. In general, these beetles attack trees 

that are greater than 8 inches in diameter at 

breast height; trees that are weakened by drought, 

competition, disease or injury; or those that are 

located near existing beetle-infested trees. Red 

turpentine beetles are common associates in pine 

trees infested with mountain, western or Jeffrey 

pine beetles. They also readily attack fire-injured 

trees and are often indicative of unhealthy root 

systems or poor soil conditions. Red turpentine 

beetle attacks do not always cause tree mortality. 

Dead or downed pines are rarely infested by any 

of these pine beetles.

Singleleaf and other pinyons: The landscape 

level pinyon pine mortality that occurred during 

2003-2004 was caused by pinyon ips. Severe 

drought was the “trigger” that initiated the 

pinyon ips outbreak, resulting in extremely high 

levels of pinyon mortality westwide.

White fir and Red fir: The fir engraver beetle 

is the principle beetle that attacks white and red 

fir. Attacks can result in top kill, branch kill or 

whole tree mortality. Trees weakened by drought, 

or other stressors are most susceptible. Root 

disease, most commonly Heterobasidion root 

disease, is often associated with these fir trees 

and serves as a weakening agent.

White fir is much more common in many 

areas than it use to be. It is a drought-intolerant, 

shade tolerant tree that readily regenerates in 

historically pine-dominated landscapes. High 

levels of white fir mortality are quite common 

during protracted and/or extreme drought 

periods.

Incense cedar: These trees are rarely killed by 

beetles alone. Typically, they are stressed by 

drought or other weather-related stressors (frost) 

long before they are attacked by bark or wood 

boring beetles.

Douglas-fir: Douglas-fir trees can be killed by 

the Douglas-fir beetle, but woodborers may be 

more commonly associated with tree mortality 

throughout much of California. Douglas-fir 

beetle readily attacks down green and fire-injured 

Douglas-fir trees and emerging beetles can cause 

high levels of tree mortality.

thinned 

stand of 

pine trees

dense stand of pine trees

differences in crown 

fullness between a healthy 

crown (left) and a poor 

crown (right).
8 Forest Health Protection – California

Step 3: Determine 

if Your Trees Have 

Been Attacked

Many signs and 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 and symptoms are described 

below. The combination of beetle attacks, gallery 

construction and feeding, and staining fungi, 

cause tree death.

Mountain, Western, and 

Jeffrey Pine Beetles

H O S T S : 

Ponderosa pine 

is attacked by 

western and 

mountain pine 

beetles. Coulter 

pine is attacked 

by the western 

pine beetle. 

Lodgepole and 

sugar pine are 

attacked by 

mountain pine 

beetles and 

Jeffrey pine is 

attacked by Jeffrey pine beetles.

Signs of beetle infestation are pitch tubes, 

small holes through the bark, or boring dust and/

or frass. Most beetle-attacked trees will have pitch 

tubes scattered over the tree bole. Pitch tubes 

resulting from successful attacks are typically 

reddish in color and vary in size depending on 

the beetle species. White or cream colored pitch 

tubes may be 

indicative of 

unsuccessful 

a t t a c k s . 

Beetles may 

attack around 

mid-bole first 

and then fill in 

up and down, 

so you need 

to examine 

the entire bole 

when looking 

for pitch tubes. 

Boring dust 

( p r o d u c e d 

by the beetle 

chewing) and 

frass (produced by the beetle feeding) is reddish 

in color but may also be yellowish or white, and 

is found mixed with resin in the pitch tubes and/

or in the bark crevices. If the tree is extremely 

water- stressed and cannot produce pitch, only 

boring dust may be visible.

The first symptom of beetle-caused tree 

mortality is typically fading needles. Needles 

on successfully attacked trees begin fading and 

change color over a period of several months. 

Attacking beetles carry blue-staining fungi into 

the tree which spreads throughout the sapwood 

and interrupts the flow of water to the crown. 

After one to several months, the sapwood also 

begins to discolor.

Bark flaking or holes in the bark caused 

by woodpeckers may commonly be found on 

infested pine trees. Removing a section of the 

bark reveals galleries created by beetles and their 

offspring. Galleries are usually packed with frass.

Red Turpentine Beetle 

HOSTS: Most pines.

The most reliable external sign that your tree 

has been attacked by red turpentine beetles is the 

presence of large pitch tubes and boring dust or 

frass on the lower bole and around the tree base. 

Pitch tubes vary in size, texture, color, and in 

the amount of boring dust and frass in the resin. 

Some pitch tubes may be as large as 2 inches 

across. Galleries between the bark and the wood 

are internal evidence of attack.

PINYON IPS

HOSTS: Most pinyon pines.

Crown fading is often the first noticeable 

symptom of attack. Closer inspection may 

reveal boring dust; very small pitch tubes may 

be observed. Attacks can occur from early spring 

through late fall and this beetle can have several 

generations per year. Galleries groove the inner 

bark surface and typically radiate from a central 

chamber. Inspection beneath the bark surface 

near the tree base during winter months may 

reveal adults feeding en masse. These beetles 

readily attack standing green trees and green 

slash.

Other IPS species

HOSTS: Pines

Most pines are also hosts to many other 

species of pine engraver (Ips sp.) beetles. They 

are not typically agressive tree killers, but given 

the right conditions, they can cause tree mortality 

and may be found in the same trees that have 

been attacked by mountain, western or Jeffrey 

pine beetle. Pine engravers tend to attack green 

pine slash, so prudent slash management should 

prevent most 

problems.

S m a l l 

piles of 

reddisho r a n g e 

boring dust 

can readily 

be seen on 

tree boles 

at the attack 

sites. Pitch 

tubes are not 

c o m m o n l y 

o b s e r v e d . 

Infested trees 

may fade the same year as the attacks occurred 

or the following spring. Under the bark, galleries 

can be observed that frequently form a “Y” or 

“H” pattern. Depth of scoring on the wood 

surface and adult beetle size vary by species.

FIR ENGRAVER

HOSTS: White fir and red fir.

Evidence of attack before crown fade is often 

hard to detect. Boring dust may be present on the 

bole but attacks may occur higher up and are not 

easily observed from the ground. Pitch tubes 

that are often formed when beetles attack pines 

are not produced on fir trees. Pitch streaming on 

the bole of the tree is not always indicative of fir 

engraver attacks. Crown fade may occur before 

attacks or beetle exit holes are visible. Attacks 

during drought periods typically result in whole 

tree mortality. However, these beetles also can 

attack strips or portions of the tree resulting in 

only branch or top kill. Adults excavate galleries 

that engrave the sapwood and run horizontal, 

cutting across the grain. Larval galleries extend at 

right angles along the grain. This gallery pattern 

is very distinctive and can be used to identify fir 

engraver attacks.

Douglas-fir Beetle

HOSTS: Douglas-fir.

The most reliable external sign that your tree 

has been attacked is the presence of boring dust 

(reddish-brown in color) near beetle entrance 

holes, in bark crevices, or around the base of the 

tree. Galleries under the bark lightly engrave the 

sapwood with adult galleries running parallel to 

the wood grain and larval galleries cutting across 

the wood grain.

Crown fade may occur the same year of 

attack or the following spring. Fresh-down trees 

and fire-injured trees are highly susceptible to 

attack. 

Red boring dust

on tree bark

Pitch tubes resulting from 

bark beetle attacks

holes in bark from 

woodpeckers feeding on 

jeffrey pine beetles
Forest Health Protection – California 9

1. Thinning trees to a wide spacing is the best long-term 

solution to increase tree health and vigor and reduce 

the likelihood of bark beetle attacks. Thinning can also 

hamper the bark beetle pheromone communication 

system that facilitates mass attacks. Residual trees 

should be the healthiest and most vigorous ones. 

Increasing age and species diversity will enhance stand 

resistance to bark beetle attacks and reduce the effects 

of tree mortality when attacks occur. Select against trees 

that have high levels of dwarf mistletoe infection. If you 

are in a drought-prone area, favor leaving trees that are 

more drought-tolerant, such as pines. Contact your forest 

health professional (see page 12) for details on proper 

thinning methods.

2. Always clean up any recently blown down trees or 

fresh slash to avoid creating more habitat for beetle 

development.

3. Avoid causing injuries to trees, such as knocking off 

bark, compacting/excavating soil near trees or disturbing 

the root system.

4. Remove all trees that currently contain beetles. The 

effectiveness of this treatment greatly depends on the 

bark beetle species, however, removing trees promptly 

when they have been successfully attacked will reduce 

the pheromone (chemicals beetles use to communicate) 

source associated with attacked trees. All infested green 

material >3 inches in diameter should be removed from 

the site, chipped, buried or burned.

5. During severe of protracted drought periods it may be 

prudent to use insecticides to protect unattacked trees. 

Applied as a preventive treatment, certain insecticides 

are effective in preventing bark beetle attacks (see page 

7). Treatments should be performed by a commercial 

applicator and limited to high value, susceptible host 

species.

6. Watering your trees during severe or protracted drought 

periods can also give your trees a boost. Watering should 

occur early in the growing season by saturating the soil 

down to two feet near the outer edge of the tree branches. 

Be careful not to over water! 

If 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. If a tree on your private land does not have the 

potential to endanger people 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 successfully attacked a tree 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. Additional tree mortality in the immediate area may 

be reduced if trees are removed while still infested. This particularly applies to Jeffrey or 

lodgepole pines.

Most bark beetles have emerged by the time trees have red-brown needles. Other 

beetles and larvae may be observed, but they are of little concern in causing mortality of 

additional trees. 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 if it hazardous to people or property.

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.

Dead Trees 

are 

“Home”

to Many

Forest 

Creatures

Stand of thinned pine trees
10 Forest Health Protection – California

Chemical Treatments

INSECTICIDES

• Carbaryl: Application of this insecticide will protect trees from the beetles described 

in this pamphlet. Due to the need for special high pressure equipment, this treatment 

is generally used only on individual, high value trees, and is generally applied by 

certified pesticide applicators. All tree bole surfaces must be completely soaked 

up to a height where the tree is too small in diameter to be suitable host material. 

On tall trees, at least 3/4 of the length of the lower bole should be treated. Note: only 

the part of the tree trunk that receives insecticide application will be protected; bark 

beetles can still attack high on the trunk if areas are left unsprayed. Carbaryl prevents 

attacks for up to two years. Contact your State or Federal forest health specialist (see 

page 12) to determine if this is an appropriate treatment for your trees. Contact your 

state’s pesticide department (see page 12) for assistance finding qualified pesticide 

applicators. Note: In California, carbaryl is a restricted-use pesticide and can only 

be applied by a certified pesticide applicator. If applying this pesticide in a different 

state, please check with your state’s Pesticide Department to determine applicable 

regulations.

• Other insecticides for bark beetles: Other insecticides such as pyrethroids are 

registered for use to prevent bark beetle attacks. Most pyrethroids prevent 

attacks for one year and some are not as effective 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.

• Other treatments: Be aware of any treatments that have not been 

scientically proven to be effective against bark beetles. If in doubt, call a 

forest health specialist. Don’t fall prey to someone claiming to be able to 

save your trees using unproven methods. Any treatments that occur after 

the tree is infested with bark beetles will NOT save your tree!

• Stump treatments can prevent Heterobasidion root disease, caused 

by the fungus Heterobasidion annosum. This disease is widespread 

throughout many areas of California and can cause mortality of infected 

trees. Windborne spores enter through stump surfaces. The fungus 

grows into the roots, causes decay, and eventually can kill the tree. The 

disease can spread from tree to tree through root contacts. The best way 

to avoid infection is prevention. Treatment of all freshly cut stumps with 

a registered borate compound prevents infection. Stumps should be 

treated immediately after trees are cut.

PESTICIDE PRECAUTIONS

Pesticides used improperly can be injurious to humans, animals, and plants. Follow directions and read all precautions on the 

label. Some states have restrictions on the use of certain pesticides and pesticide registrations are under constant review by 

the Federal Environmental Protection Agency so please consult your local County agriculture agent or State extension agent 

prior to any applications.

EXPLANATION OF UNFAMILIAR TERMS

boring dust – produced by beetles chewing through material but not feeding on it (see frass below)

conifer - any tree that produces seeds in cones

dwarf mistletoe – parasitic flowering plants that grow in tree bark and wood, absorbing water and nutrients of the host tree that 

otherwise are used for growth (see http://ceres.ca.gov/foreststeward/pdf/treenote11.pdf for more information)

frass – produced by beetles feeding on material (the solid form of insect excrement)

gallery – a tunnel or pathway in host tissue in which an insect lives, feeds, mates, and/or deposits eggs

group kill – a group of trees killed by bark beetles during the same time period or over multiple years

pheromone – a chemical produced by insects (and other animals) that serves as a signal between members of the same species

pitch tube – a mixture of tree resin, other tree bole components (bark, xylem, phloem), and frass and boring dust that forms on the 

outside surface of the bark when a tree is attacked by bark beetles

slash - branches and other woody material left after cutting a tree

tree bole – the trunk or main stem of a tree

insecticide application on tree bole 

to prevent bark beetle attacks

borate compound on stump to prevent 

infection by HETEROBASIDION SP.
Forest Health Protection – California 11

Federal and State 

Land Managers

Effective management of bark beetles and 

vegetation is a difficult challenge. Federal and 

State land managers know a great deal regarding 

characteristics that make stands susceptible 

to bark beetles. 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 preventive vegetation management. 

Treating vast areas such as entire National Forests 

with chemicals to reduce bark beetle populations 

is not practical, feasible, or desirable.

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 vegetation and bark 

beetles are limited.

Where vegetation management activities are 

permitted, Federal and State land managers can 

reduce the likelihood of high levels of bark beetlecaused tree mortality. Examples of management 

activities being implemented to reduce forest 

susceptibility to bark beetles include: 

• Thinning out some of the trees in dense 

stands to improve tree vigor and reduce 

susceptibility to bark beetles. 

• Promoting a diversity of tree species, which 

also reduces stand susceptibility to bark 

beetles.

• Promoting a diversity of age classes. 

• Promoting drought tolerant species.

Private Landowners

Private landowners have different objectives 

for their property and trees and have their own 

opinion about possible management techniques. 

Challenges of a Bark Beetle Outbreak – 

What are Land Managers Doing?

The U.S. Department of Agriculture (USDA) prohibits 

discrimination in all its programs and activities on the 

basis of race, color, national origin, age, disability, and 

where applicable, sex, marital status, familial status, 

parental status, religion, sexual orientation, genetic 

information, political beliefs, reprisal, or because all 

or part of an individual’s income is derived from any 

public assistance program. (Not all prohibited bases 

apply to all programs). Persons with disabilities who 

require alternative means for communication of program information (Braille, large print, audio tape, etc.) 

should contact USDA’s TARGET Center at (202) 720-

2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 

1400 Independence Avenue, S.W., Washington, D.C., 

20250-9410, or call (800) 795-3272 (voice) or (202) 

720-6382 (TDD). USDA is an equal opportunity provider and employer.

Some will choose to do nothing; others will adopt 

bark beetle prevention strategies that may include 

thinning and the use of insecticides. Thinning 

during normal precipitation years is better than 

waiting to thin during a drought when trees are 

stressed and bark beetle-caused tree mortality 

is on the rise. Insecticide treatments need to 

be applied prior to beetle attack and additional 

applications may be required if drought or other 

stress-causing conditions persist.
12 Forest Health Protection – California

Where to go for help

or additional information

ORGANIZATIONS

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

private lands:

CALIFORNIA

- Don Owen, CAL FIRE, 530.224.2494, don.owen@fire.ca.gov

- Tom Smith, CAL FIRE, 916.599.6882, tom.smith@fire.ca.gov

- Kim Corella, CAL FIRE, 808.550.8583, kim.camilli@fire.ca.gov

- Chris Lee, CAL FIRE, 707.726.1254, christopher.lee@fire.ca.gov

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

Federal lands.

Northeastern CA

Danny Cluck, USDA Forest Service, Forest Health Protection,

530.252.6431, dcluck@fs.fed.us

Northwestern CA

Cynthia Snyder, USDA Forest Service, Forest Health Protection,

530.226.2437, clsnyder@fs.fed.us

South Sierras

Beverly Bulaon, USDA Forest Service, Forest Health Protection,

209.532.3671, ext. 323, bbulaon@fs.fed.us

Southern CA

Tom Coleman, USDA Forest Service, Forest Health Protection,

909.382.2871, twcoleman@fs.fed.us

■ For information on professional pesticide applicators and insecticide registration 

contact your County Agriculture Commissioner’s Office and see: California 

Department of Pesticide Regulation: www.cdpr.ca.gov

■ For general National Forest information: www.fs.usda.gov/main/r5/about-region/

offices

■ For information on USDA FS Forest Health Protection programs in California:

www.fs.usda.gov/main/r5/forest-grasslandhealth

■ Additional pictures of various trees and insects: www.bugwood.org/ or www.

forestryimages.org

PUBLICATIONS

■ Bark Beetles and Vegetation Management in CA: www.fs.usda.gov/Internet/FSE_

DOCUMENTS/fsbdev3_045320.pdf

■ Forest Insect and Disease Leaflets: www.fs.usda.gov/goto/fhp/fidls

■ Tree Notes: http://calfire.ca.gov/foreststeward/treenotes.html

■ California Forest Pest Conditions: www.fs.usda.gov/detail/r5/forest-grasslandhealt

h/?cid=fsbdev3_046704

All photos in this publication are are in the public domain and were taken by the 

USDA Forest Service.

The USDA Forest Service is an equal opportunity service provider and employer.

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. Most of the vegetation 

in California has evolved with fire and, in 

many cases, relies on fire to sustain its health 

and presence on the landscape. However, fire 

around your home or other infrastructures is 

usually not desirable. 

The most critical factors for a home 

surviving a wildfire are the construction of 

the home and the vegetation near the home.

California’s Fire Safe Councils 

preserve and enhance human made and 

natural resources by providing leadership 

and support to mobilize all Californians 

to protect their homes, communities and 

environments from wildfires. As a result 

of the Councils’ efforts, thinning and fuel 

reduction treatments have been implemented 

on privately owned acres across the State. 

The Fire Safe Council membership consists 

of fifty public and private organizations. For 

more information regarding this successful 

and diverse collaborative effort, please go 

to http://www.firesafecouncil.org/index.cfm. 

Some general recommendations are:

1. Roofs should be made of non-flammable 

material.

2. Enclose places where fire embers 

can 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.

For more information regarding

protecting your home from

wildfire 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. This publication was 

modified from one produced for the Intermountain West. Questions regarding this publication can be 

directed to Sheri Smith, Regional Entomologist, at ssmith@fs.fed.us or 530.252.6667.