Figure 6—Bark beetle galleries form an iden-
tifying pattern. Mountain pine beetle egg
galleries are vertical. The larvae construct
their feeding galleries at right angles to the
egg galleries.

Life History

The beetle develops through four
stages: egg, larva, pupa, and adult.
Except for a few days during the
summer when adults emerge and fly
to new trees, all stages are spent
under the bark of infested trees.

The beetle usually takes 1 year to
complete its life cycle. However, at
high elevations where summer
temperatures are cool, 2 years may
be required to complete the life cycle.
And in California, two generations
may be produced in | year in low-
elevation sugar pines.

Under the bark, female beetles
construct straight, vertical egg
galleries. Packed with boring dust,
these galleries are mostly in the
phloem, or inner bark, although they
slightly score the sapwood. They range
from 4 to 48 inches (10 to 122 cm)
long, averaging about 10 inches (25
cm) (fig. 6).

Females lay tiny, pearl-white eggs
in niches along the sides of the
galleries, usually during the summer
and early fall. The eggs hatch in 10 to
14 days, although they may take
longer during cool weather. (See
cover photo.)

Sometimes, eggs are also laid in
late spring by females that survived
the winter. Surviving females may
either reemerge and reattack trees or
merely extend their egg galleries.

The legless larvae are white with
brown heads. This stage lasts for
about 10 months—from August to
the following June. The larval
broods feed on the phloem, con-
structing galleries that extend at right
angles to the egg galleries. When
mature, larvae excavate oval cells in


Salvage can retrieve wood that
otherwise would be lost, and if
beetles are removed with the tree and
disposed of, some reduction in the
beetle population can be expected.
However, once a large outbreak has
developed, salvage logging of in-
fested material to reduce future tree
mortality generally will not be effec-
tive.

Insecticides. Insecticides are avail-
able for direct control of beetles in in-
fested trees. The use of insecticides in
such situations requires the combined
efforts of all landowners within the
designated management area. How-
ever, if beetle outbreaks are large, di-
rect chemical control may not be cost
effective: treatment costs may exceed
the value of the wood apparently
saved. At best, insecticides provide a
temporary control measure that slows
infestations. They will not stop an out-
break as long as the susceptible stands
remain unaltered.

Preventive spraying before trees
become infested will protect in-
dividual high-value trees. Such
preventive treatment does not require
a united effort by landowners as does
the treatment of infested trees.
However, periodic treatments will be
necessary for as long as the outbreak
lasts.

Insecticides are reviewed con-
tinuously by the U.S. Environmental
Protection Agency; persons con-
templating the use of insecticides
should ensure that they are still
registered.

Attractants. Synthetic beetle attrac-
tants are now available to manipulate
and monitor small outbreaks. Baiting
and trapping with attractants, man-
agers can contain small spot infesta-
tions, thus preventing their spread into
susceptible stands and maintaining
beetle populations at low levels until
roads can be built, allowing for stand
management. Using these new tools,
managers can also protect high-value
campgrounds and other recreation
sites.

Information. Private landowners
can get information about mountain
pine beetle management from a Coop-
erative Extension agent at their land-
grant college, a State agricultural ex-
periment station, a county Extension
office, the local State forestry office,
or the Forest Pest Management staff,
U.S. Department of Agriculture, For-
est Service. Federal resource managers
should contact the Forest Pest Manage-
ment staff in their area.


Tree Resistance. A copious pitch
flow from some pines can prevent suc-
cessful attack. In effect, the beetles
drown in the pitch as they bore into the
inner bark or must abandon the tree.
The number of attacking beetles, the
characteristics of the tree, and the
weather affect a tree’s ability to pro-
duce enough resin to resist attack. But
if a large number of beetles attack a
tree, the beetles can successfully over-
come the tree’s ability to pitch them
out.

Predators and Parasites. Nema-
todes, internal parasitic worms, can
hinder or prevent egg production.
Other nematodes feed on eggs after
they are laid by the females.

Woodpeckers feed heavily on larvae
in some trees. Woodpeckers, in their

search for larvae, make holes in the
bark, causing the bark to dry and thus
killing additional beetles. Woodpeck-
ers probably play a role in reducing
beetle numbers during endemic periods
but do not control the beetles during
epidemics. Several other bird species,
including nuthatches, feed on adults
exposed during flight or as they attack.

A dolichopodid fly and two
species of checkered beetles (fig. 8)
are common predators: they may
reduce beetle numbers in individual
trees but seldom affect mountain
pine beetle infestations. Parasitic
wasps sometimes cause substantial
mortality in trees where their short
ovipositors can reach the larvae
through the thin bark.

Figure 8—A checkered beetle (Enoclerus
sphegeus Fabricius) eating a mountain pine
beetle adult.


which they turn into pupae. By July,
the pupae usually have been
transformed into adults.

Adults feed within the bark before
they emerge; when several feeding
chambers coalesce, adults occur in
groups. One or more beetles will then
make an exit hole (fig. 7) from which
several adults will emerge. Within 1
or 2 days after emerging, the beetles
will attack other trees.

Figure 7—Exit holes, about 3/32 inch (2.4
mm) in diameter, made by mountain pine
beetles.

Unmated female beetles making
the first attacks release chemicals
called aggregating pheromones.
These pheromones attract males and
other females until a mass attack
overcomes the tree. Adjacent trees
are then infested.

Attacking beetles carry with them
the spores of blue-staining fungi on
their bodies and in a special structure
on their heads. As the fungi develop
and spread throughout the sapwood,
they interrupt the flow of water to
the crown. The fungi also reduce the
tree’s flow of pitch, thus aiding the
beetles in overcoming the tree. The
combined action of both beetles and
fungi causes the tree to die and the
needles to discolor.

Factors Affecting Outbreaks

A number of factors can affect the
size of mountain pine beetle popula-
tions.

Food Supply. The food supply reg-
ulates populations of the beetle.
Beetles usually select larger lodgepole
pines that have thick phloem. They
need adequate food, found in large-
diameter trees, for their population to
build up. After the larger lodgepole
pines are killed, beetles infest smaller
and smaller trees, where phloem is thin
and excessive drying occurs. Beetle
populations then decline to endemic
levels.

The relationship between beetle
populations and phloem thickness has
not been established for other iree
species.


Figure 10—High-risk ponderosa pine stands
attacked by the beetle. Trees with yellow
foliage have been recently attacked; gray
trees were killed the year before the trees with
yellow foliage were attacked.

High-risk lodgepole pine stands
have an average age of more than 80,
an average diameter at breast height
of more than 8 inches (20 cm), and a
suitable climate for beetle develop-
ment based on elevation and latitude.

In second-growth ponderosa pine,
high-risk stands have a high stand
basal area, a single story, and an
average diameter at breast height
more than 10 inches (25 cm) (fig. 10).

Control

Control options available for
managing the mountain pine beetle
depend somewhat on the size of the
outbreak, the age of the stand, the
size of the trees, and the conditions
of the site.

Silviculture. Silvicultural control
measures are the most efficient.

Thinning stands of lodgepole and
ponderosa pines will prevent or
minimize beetle-caused mortality.
Patch cutting in lodgepole pine
stands creates a mosaic of age and
size classes, which reduces the
acreage of lodgepole pine that will be
highly susceptible to beetles at one
time.

Where clear or patch cutting is not
feasible, selective harvesting will help
reduce mortality. Trees can be
harvested selectively in riparian
zones and in areas along roads, in
campgrounds, and around scenic
vistas.


Forest Insect
& Disease
Leaflet 2

U.S. Department
of Agriculture
Forest Service

Mountain Pine Beetle

Gene D. Amman,! Mark D. McGregor,? and Robert E. Dolph, Jr.>

'Principal entomologist, U.S. Department of
Agriculture, Forest Service, Intermountain
Forest and Range Experiment Station, Ogden,
UT.

?Entomologist, U.S. Department of Agricul-
ture, Forest Service, Cooperative Forestry and
Pest Management, Northern Region, Missoula,
MT.

3Entomologist, U.S. Department of Agricul-
ture, Forest Service, Forest Pest Management,
State and Private Forestry, Pacific Northwest
Region, Portland, OR.

The mountain pine beetle, Dendroc-
tonus ponderosae Hopkins, is a mem-
ber of a group of beetles known as bark
beetles. Except when adults emerge
and attack new trees, the mountain
pine beetle completes its life cycle
under the bark.

The beetle attacks and kills lodge-
pole, ponderosa, sugar, and western
white pines. Outbreaks frequently de-
velop in lodgepole pine stands that



Pesticides used improperly can be injurious to human beings, animals,
and plants. Follow the directions and heed all precautions on labels. Store
pesticides in original containers under lock and key—out of the reach of children
and animals—and away from food and feed.

Apply pesticides so that they do not endanger humans, livestock. crops,
beneficial insects, fish, and wildlife. Do not apply pesticides where there is
danger of drift when honey bees or other pollinating insects are visiting plants.
or in ways that may contaminate water or leave illegal residues

Avoid prolonged inhalation of pesticide sprays or dusts: wear protective
clothing and equipment. if specified on the label

If your hands become contaminated with a pesticide, do not eat or drink
until you have washed. In case a pesticide is swallowed or gets in the eye
follow the first aid treatment given on the label. and get prompt medical
attention. If a pesticide is spilled on your skin or clothing, remove clothing
immediately and wash skin thoroughly.

NOTE: Some States have restrictions on the use of
certain pesticides. Check your State and local regula-
tions. Also, because registrations of pesticides are under

constant review by the U.S Environmental Protection

>
CAUTION:
Pesrices|
Agency, consult your local forest pathologist. county
agriculture agent, or State extension specialist to be sure

the intended use is still registered

Revised June 1985


References

Amman, Gene D.; Cole, Walter E. Mountain
pine beetle dynamics in lodgepole pine for-
ests. Part II: population dynamics. Gen. Tech.
Rep. INT-145. Ogden, UT: U.S. Department
of Agriculture, Forest Service, Intermountain
Forest and Range Experiment Station; 1983.
59 p.

Amman, Gene D.; McGregor, Mark D.; Cahill,
Donn B.; Klein, William H. Guidelines for
reducing losses of lodgepole pine to the moun-
tain pine beetle in unmanaged stands in the
Rocky Mountains. Gen. Tech. Rep. INT-36.
Ogden, UT: U.S. Department of Agriculture,
Forest Service, Intermountain Forest and
Range Experiment Station; 1977. 19 p.

Berryman, Alan A.; Amman, Gene D.; Stark,
Ronald W., eds. Theory and practice of
mountain pine beetle management in lodge-
pole pine forests: Proceeding of a symposium;
1978 April 25-27; Pullman, WA. Moscow,
ID: University of Idaho, Forest, Wildlife and
Range Experiment Station; 1978. 224 p.

Borden, J. H.; Chong, L. J.; Pratt, K. E. G.;
Gray, D. R. The application of behavior-
modifying chemicals to contain infestations of
the mountain pine beetle, Dendroctonus pon-
derosae. Forestry Chronicle. 1983 October:
235-239.

Cole, Walter E. Some risks and causes of mor-
tality in mountain pine beetle populations: a
long-term analysis. Researches in Population
Ecology. 23(1): 116-144; 1981.

Cole, Walter E; Amman, Gene D. Mountain
pine beetle dynamics in lodgepole pine for-
ests. Part I: course of an infestation. Gen.
Tech. Rep. INT-89. Ogden, UT: U.S. De-
partment of Agriculture, Forest Service, Inter-
mountain Forest and Range Experiment Sta-
tion; 1980. 56 p.

Cole, Walter E.; McGregor, Mark D. Estimating
the rate and amount of tree loss from mountain
pine beetle infestations. Res. Pap. INT-318.
Ogden, UT: U.S. Department of Agriculture,
Forest Service, Intermountain Forest and
Range Experiment Station; 1983. 22 p.

McCambridge, William F.; Hawksworth, Frank
G.; Edminster, Carleton B.; Laut, John G.
Ponderosa pine mortality resulting from a
mountain pine beetle outbreak. Res. Pap.
RM-235. Fort Collins, Ct -S. Department
of Agriculture, Forest Service, Rocky Moun-
tain Forest and Range Experiment Station;
1982. 7 p.

McGregor, M. D.; Amman, G. D.; Cole, W. E.
Hazard-rating lodgepole pine for susceptibil-
ity to mountain pine beetle infestation. In:
Hedden, R. L.; Barras, S. J.; Coster, J. E.
Hazard-rating systems in forest insect pest
management: Proceedings of a symposium;
1980 July 31-August 1; Athens, GA. Gen.
Tech. Rep. WO-27. Washington, DC: U.S.
Department of Agriculture, Forest Service;
1981: 99-104,

Safranyik, L.; Shrimpton, D. M.; Whitney,
H. S. Management of lodgepole pine to re-
duce losses from the mountain pine beetle.
Tech. Rep. 1. Victoria, BC: Canadian For-
estry Service, Pacific Forest Research Centre,
Department of the Environment; 1974. 24 p.

Sartwell, C.; Dolph, R. E., Jr. Silvicultural and
direct control of mountain pine beetle in
second-growth ponderosa pine. Res. Note
PNW-268. Portland, OR: U.S. Department of
Agriculture, Forest Service, Pacific North-
west Forest and Range Experiment Station;
1976. 8 p.

Stevens, R. E.; McCambridge, W. F.; Edmin-
ster, C. B. Risk rating guide for mountain pine
beetle in Black Hills ponderosa pine. Res.
Note RM-385. Fort Collins, CO: U.S. De-
partment of Agriculture, Forest Service,
Rocky Mountain Forest and Range Experi-
ment Station; 1980. 2 p.

Struble, George R. Attack pattern of mountain
pine beetle in sugar pine stands. Res. Note
PSW-60. Berkeley, CA: U.S. Department of
Agriculture. Forest Service, Pacific South-
west Forest and Range Experiment Station;
1965. 7 p.



Figure 9—Larvae of the round-headed wood-
borer (see larva near top of photo) have
devoured both the phloem and the mountain
pine beetle brood.

Competition. Larvae compete for
food and space not only with each
other but with larvae of other beetles.
For example, the larvae of the round-
headed woodborers, feeding within the
inner bark, occasionally destroy almost
all of the mountain pine beetle brood
found there (fig. 9).

Cold Temperature. Unseasonably
low temperatures may retard out-
breaks. Early autumn or mid-spring
temperatures of about 0 °F (—18 °C)
and winter temperatures below —34 °F
(—37 °C) may affect outbreaks.

Unfortunately, such cold
temperatures may affect only low-
lying areas; beetles survive on
warmer slopes. Beetles in thick-
barked trees and in portions of tree
trunks that are below the snow line

are also protected from the cold and
more likely to survive.

Stand Hazard Rating

Resource managers can take ap-
propriate action to prevent outbreaks
or reduce damage if they can identify
those stands having characteristics
that lead to bark beetle infestations.
This process of risk assessment is
called hazard rating, and several
methods of hazard rating pine stands
are available. These methods are based
on characteristics frequently associated
with epidemics. Computer models are
available to predict losses to mountain
pine beetle based on stand structure
and habitat type. It is still not possible,
however, to predict when stands will
become infested.


When the beetles attack, they carry
blue-staining fungi into the tree. After
one to several months, the sapwood
begins to discolor (fig. 4).

Woodpeckers, feeding on larvae
under the bark, make individual
holes in thick bark, or they may par-
tially or completely remove thinner
bark. These signs, plus the resulting
pile of bark flakes around the base of
the tree, are good evidence of bark
beetle infestation.

The first sign of beetle-caused
mortality is generally discolored
foliage. Needles on successfully in-
fested trees begin fading and chang-
ing color several months to 1 year
after the trees have been attacked.
The needles change from green to
yellowish green, then sorrel, red, and

Figure 5—Dying trees. Discolored foliage is a
sign that these lodgepole pines have been at-
tacked and killed by the mountain pine beetle.

finally rusty brown (fig. 5). Fading
begins in the lower crown and pro-
gresses upward.

In large sugar pines, fading in the
upper crown is the first evidence of
infestation.

Figure 4—Sapwood has been discolored by
blue-staining fungi; heartwood is not stained.



Evidence of Infestation

The mountain pine beetle begins
attacking most pine species on the
lower 15 feet (4.4 m) of the trunk.
Trees are generally killed by beetles
of a single generation.

However, large sugar pines are
first attacked in the crown. Two or
more generations of beetles—each
generation attacking a lower por-
tion—may occur before the tree is
killed.

Examination of infested trees
usually reveals the presence of pitch
tubes. Pitch tubes are made when
female beetles bore into the tree.
There are two types of tubes. Pitch
tubes on successfully infested trees
are cream to dark-red masses of resin
mixed with boring dust and are one-
fourth to one-half inch (6 to 13 mm)
in diameter. Pitch tubes on unsuc-
cessfully infested trees are larger,
three-fourths of an inch to 1 inch (19
to 25 mm) in diameter, and widely
scattered over the trunk. When beetles
are not present in sufficient numbers,
trees can produce enough resin to
“pitch out” beetles as they bore into the
inner bark (fig. 2).

Besides having pitch tubes,
successfully infested trees will have
dry boring dust, similar to fine
sawdust, in bark crevices and around
the base of the tree (fig. 3).
Sometimes, however, infested trees
can have boring dust, but not pitch
tubes. These trees, called blind at-
tacks, are common during drought
years when trees produce little pitch.

Figure 2—Unsuccessfully attacked tree has
“pitched out” beetle.

Figure 3—Pitch tubes on the trunk and bor
ing dust around the base indicate that this
lodgepole pine has been attacked and killed
by the beetle.


contain well-distributed, large-
diameter trees or in dense stands of
pole-sized ponderosa pine. When out-
breaks are extensive, millions of trees
may be killed each year. Periodic
losses of high-value, mature sugar and
western white pines are less wide-
spread but also serious.

During epidemics, widespread tree
mortality alters the forest ecosystem.
Often, beetles have almost totally
depleted commercial pine forests
and, in some cases, have converted
valuable forests to less desirable
timber species, such as subalpine fir.
Sometimes, forested areas are con-
verted to grass and shrubs. The pro-
fusion of beetle-killed trees can
change wildlife species composition
and distribution by altering hiding
and thermal cover and by impeding
movement. Tree mortality may in-
crease the water yield for several
years following an_ infestation.
Moreover, the dead trees left after
epidemics are a source of fuel that
will, in time, burn unless removed.

Range and Hosts

The beetle is native to North
America. It is found in an area from
the Pacific Coast east to the Black
Hills of South Dakota and from nor-
thern British Columbia and western
Alberta south into northwestern
Mexico (fig. 1). Its habitat ranges
from near sea level in British Colum-
bia to 11,000 feet (3,353 m) in
southern California.

The four major hosts of the moun-
tain pine beetle are lodgepole,
ponderosa, sugar, and white pines.

Figure 1

Mountain Pine Beetle

Figure 1—Probable distribution of the moun-
tain pine beetle in North America.

Limber, Coulter, foxtail,
whitebark, pinyon, and bristlecone
pines are also infested and killed.
Scotch pine, an exotic in North
America, is highly susceptible to at-
tack. Douglas-fir, true firs, spruce,
larch, and incense cedar are occa-
sionally attacked, but because they
are not true hosts, broods rarely
develop. Attacks on nonhost trees
usually occur when nearby pines are
heavily infested.