evidence of Infestation

Examination of infested trees usually 

reveals the presence of pitch tubes on the 

lower 15 feet of the trunk. Pitch tubes 

are made when female beetles bore into 

the tree. Healthier trees which are attacked may “pitch out” beetles, resulting 

in unsuccessful attacks. Removing outer 

bark to reveal successful galleries and/or 

developing broods are the surest way to 

confi rm successful attacks.

Besides having pitch tubes, trees that 

have been successfully infested will have 

dry boring dust, similar to fi ne sawdust, 

in bark crevices and around the base. 

Usually, the spring after a tree has been 

successfully attacked, it begins to “fade.” 

Foliage typically turns yellowish, then 

reddish-orange, and fi nally reddishbrown. After two or three years most 

needles have fallen from the dead tree. 

Fading is weather dependent, and also 

somewhat dependent upon individual 

tree’s characteristics. Generally, fading is 

not readily apparent until the spring following an attack.

Pitch 

tubes on 

trunk of 

infested 

trees.

during July and August. The beetle fl ight 

period is weather-dependant and may be 

lengthened or shortened by abnormally 

high or low temperatures, respectively. 

The female beetle initiates attacks. Once 

the female 

attracts a 

male and 

mates, she 

constructs 

a vertical 

egg gallery 

beneath the 

tree’s bark, 

paralleling 

the grain of 

the wood. 

Egg galleries can be 

up to 48 

inches long 

and are 

packed with boring dust and frass. Eggs 

are laid in niches along both sides of the 

gallery and hatch within two weeks.

Larvae begin feeding at right angles to 

the egg gallery, fi rst within the inner bark 

(phloem). By the following June, they 

mature and begin to feed more deeply 

into the bark. There they construct pupal 

chambers, pupate, and complete their 

development by mid- to late- summer. 

Newly matured adults chew exit holes, 

make new attacks, and renew the yearly 

cycle.

i

ntroduction

The most important native bark beetle 

pest of mature pines in the Western 

United States is the mountain pine beetle, 

Dendroctonus ponderosae Hopkins. These 

beetles infest and kill their hosts: lodgepole, ponderosa, whitebark and western 

white pines, throughout their range in 

the Intermountain West. Douglas-fi r, true 

fi rs, spruce, larch and cedar may be attacked during beetle outbreaks, but brood 

development is rare. Epidemics can build 

rapidly and kill hundreds to millions of 

mature trees each year.

description

The mountain pine beetle goes through 

four distinct life stages: egg, larva, pupa 

and adult. Eggs are oval, pearly white, 

and about the size of the head of a pin. 

Larvae are yellowish-white, legless grubs 

with a red-brown head capsule. Larvae 

undergo four size changes (instars) as they 

mature. Pupae are white and more closely 

resemble adults. Immature adults (callow adults) are tan colored, but darken 

to nearly black before emergence. Adults 

are cylindrically shaped, about one-fourth 

inch long, and can fl y.

life History and Habits

The mountain pine beetle has one generation per year and typically takes one 

year to complete its life cycle. Most over 

winter as larvae. Adults emerge from their 

host tree and infest susceptible trees

Mountain pine beetle galleries. Mountain pine beetle galleries.

Mountain Pine 

Beetle in the 

Intermountain 

West

A “group” of mountain pine beetle killed-trees 

may number from a few to thousands. 

United States Department of Agriculture

Forest Service

Intermountain Region
Photo credits: Forest Health Protection, Northern Region, Missoula, 

Montana.

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

in all its programs and activities on the basis of race, color, 

national origin, gender, religion, age, disability, political beliefs, 

sexual orientation, and marital or family status. (Not all prohibited 

bases apply to all programs.) Persons with disabilities who require 

alternative means for communication of program information (Braille, 

large print, audiotape, etc.) should contact: USDA’s TARGET Center 

at 202-720-2600 (voice and TDD).

To fi le a complaint of discrimination, write USDA, Director, Offi ce of 

Civil Rights, Room 326-W, Whitten Building, 14th and Independence 

Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 

(voice or TDD). USDA is an equal opportunity provider and employer.

30.04.400.06/00

For additional information, contact 

any USDA Forest Service or

State Forestry Offi ce in your area

Forest Health Protection

Intermountain Region

Boise Field Offi ce

(208) 373-4227

conclusion

Long-term management of pine forests 

offers the best means of preventing or 

minimizing damage by the mountain 

pine beetle. Immature stands should be 

periodically thinned to maintain vigorous tree growth, reduce moisture stress, 

and remove trees damaged by weather, 

disease, or other agents. Mature or 

over-mature stands growing in areas 

actively managed, should be considered 

for regeneration. At that time it may be 

appropriate to consider the introduction 

of non-host tree species to the site. 

In non-Wilderness areas, sound and 

timely silvicultural practices – to include 

salvage of infested trees before beetles 

emerge from them – can prevent bark 

beetle outbreaks. 

If the beetles are removed with salvaged 

wood and disposed of, some reduction 

in the beetle population can be expected. 

However, once a large outbreak has 

developed, salvage logging of infested 

material to reduce future tree mortality 

generally will not be effective. 

Insecticides: Spraying before trees 

become infested will protect individual, 

high-value trees. Such preventive treatment will be necessary for as long as the 

outbreak lasts. 

These insecticides are reviewed continuously by the U.S. Environmental Protection Agency. Persons contemplating the 

use of such insecticides should ensure 

that they are properly registered.

Pheromones: Pheromones are beetle-produced chemicals emitted to either attract 

a mate or affect populations to their 

advantage. Female beetles making an 

initial attack, use these attractant pheromones to attract the males. Beetles also 

produce anti-aggregating pheromones, 

which repel future attacks once a particular tree contains all the beetles it can 

support. Synthetic beetle attractants are 

now available to manipulate and monitor 

small outbreaks.

management Options

Options for managing mountain pine 

beetle depend on the size of the outbreak, 

the age of the stand, the size of the trees, 

and the conditions of the site.

Silvicultural Alternatives: Over mature 

pine stands of large diameter, densely 

stocked trees are more likely to experience a devastating beetle outbreak than 

stands of other conditions. 

Thinning stands of lodgepole and 

ponderosa pine can prevent or minimize 

beetle-caused mortality. Patch cutting in 

lodgepole pine stands creates a mosaic of 

tree age and sizes, and reduces acreages 

highly susceptible to beetles at one time. 

Where clear or patch cutting is not 

feasible, selective harvesting can help 

reduce mortality. Trees can be harvested 

selectively within a riparian zone, along 

roads, in campgrounds, and around 

scenic vistas. 

High hazard lodgepole pine stand.