Dendroctonus ponderosae
(black hills beetle)

This insect has not yet appeared outside its geographic range, therefore it can only be considered as potentially invasive.

D. ponderosae is widely distributed in the western USA, British Columbia and southwestern Alberta, Canada, and Baja California, Mexico.

The adult mountain pine beetles are relatively strong fliers and can fly at least 2-3 km in search of new hosts. However, emerging beetles often prefer to attack trees adjacent to the tree from which they emerged. In addition, their small size allows them to disperse on air currents. Other life stages are confined to the cambium layer and inner bark, and are not naturally dispersed.

Pathways for human-assisted dispersal include the transport of unprocessed pine logs or lumber, crates, pallets and dunnage, containing bark strips. It is conceivable that the larvae, pupae and overwintering adults could survive an ocean voyage and be introduced into a new location. Provided that suitable hosts are available for colonization, this insect could become established and, in the absence of natural enemies, cause significant damage. The mountain pine beetle has reportedly been intercepted in Australia (EPPO, 2003). The related North American red turpentine beetle, Dendroctonus valens, has recently been introduced to and has established in, China. Since then it has killed more than 6 million pines there (Sun et al., 2003).

In Pinus ponderosa (ponderosa pine), the mountain pine beetle prefers to attack forests that are overstocked, primarily as a result of the exclusion of naturally occurring fires. Trees with large diameters and infested with dwarf mistletoe, Arceuthobium sp., are especially vulnerable to attack.

In Pinus contorta (lodgepole pine), the mountain pine beetle typically attacks pure, even-aged forests of 60- to 80-years-old. Trees with large diameters and thick bark are preferred.

In Pinus monticola (western white pine) and Pinus lambertiana (sugar pine) forests, attacks occur in over-mature forests, often following periods of moisture deficit.

The mountain pine beetle can attack any species of Pinus within its geographic range. The primary hosts, on the basis of their economic importance and frequency of attack, are: lodgepole pine, Pinus contorta var. murrayana; ponderosa pine, Pinus ponderosa; sugar pine, Pinus lambertiana; and western white pine, Pinus monticola (Amman et al., 1985). During outbreaks, occasional attacks have been found in mountain spruce, Picea engelmannii (Wood, 1982). Secondary hosts include Pinus albicaulis, Pinus balfouriana, Pinus coulteri (Coulter pine), Pinus edulis (Pinyon pine), Pinus flexilis (limber pine), Pinus monophylla (single-leaf pinyon), Pinus strobiformis (Mexican white pine), Pinus sylvestris (Scotch pine), and rarely, Pinus jeffreyi (Jeffrey pine) (Wood, 1982; Amman et al., 1985).

Life History and Habits

The genus, Dendroctonus, consists of 19 species worldwide. Most of these occur on conifers in North and Central America. Dendroctonus armandi (native to China) and Dendroctonus micans, are found in Palearctic conifer forests (Wood, 1982). Several species are important forest pests, capable of reaching epidemic levels and killing thousands of trees. The genus, Dendroctonus, contains some of the most destructive forest insects in North and Central America.

The mountain pine beetle usually takes 1 year to complete a generation. However, at high elevations, where summer temperatures are cool, 2 years may be required for completion. In California, two generations may be produced in a single year, in low elevation sugar pine (Pinus lambertiana) forests.

Unmated females initiate the attacks on host trees, and release pheromones that stimulate mass attack, and attract males into the entrance holes that they construct. The mountain pine beetle begins to attack most pines on the lower 4.4 m of the trunk. An exception is the large P. lambertiana, which is initially attacked in the crown. Two or more generations of beetles, each attacking a lower portion of the tree, may occur before the tree is killed.

After mating, the female beetles construct straight, vertical egg galleries, mostly in the phloem or inner bark. The egg galleries slightly score the sapwood. The galleries range from 10 to 122 cm long (average of 25 cm) and are packed with frass. The females lay eggs in niches, on the sides of the galleries, usually during the summer or early autumn.

Typically the eggs hatch in 10-14 days, although they may hatch later during cool weather. The larval stage lasts about 10 months, from August to June. The larvae feed in the phloem and construct feeding galleries at right angles to the egg galleries. When mature, they excavate oval cells in which they pupate. The pupae transform into adults in July.

Callow adults feed in the bark before they emerge and exit the tree via round exit holes. New trees are attacked within 1-2 days after emergence (Amman et al., 1985).

The attacking adults carry spores of the blue stain fungus, Ceratocystis minor [Ophiostoma minor], in special pouch-like structures in their heads, known as mycangia. As the adults chew through the bark, the fungal spores dislodge and germinate in the sapwood. Tree death is a result of the girdling action of the adults and larvae, in combination with the blue stain, which blocks the tree's conductive vessels (Amman and Cole, 1983).

A number of natural enemies of D. ponderosae have been documented. However, the natural enemies of this insect are believed to be most important in regulating it at low population levels. During outbreaks, natural enemies appear to be less able to exert a significant influence on the populations (Bellows et al., 1998). Several species of woodpeckers are known to strip the bark from infested trees, and feed on the larvae and pupae (Furniss and Carolin, 1977; Amman et al., 1985).

The bark surface should be inspected for pitch tubes and/or boring dust. The cambium and inner bark of unprocessed logs or dunnage, and crating or pallets, containing bark strips, should be inspected for the presence of galleries and insect life stages.

D. ponderosae is similar to Dendroctonus jeffreyi and is differentiated by the presence of large, conspicuous punctures on the pronotum. These punctures are separated by spaces that are at least twice as large as the diameter of the puncture (Wood, 1982). To ensure positive identification, a taxonomist, with expertise in the family Scolytidae, should examine bark beetles believed to be a new introduction.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control

The control of tree-stocking levels, through cultural tactics, is considered to be the most important factor in preventing the occurrence of outbreaks (Cole and Amman, 1980).

In Pinus contorta (lodgepole pine) forests, the objective of cultural control is to remove high-risk trees. High-risk trees are those with a large diameter (>25 cm) and thick phloem. Partial cutting is preferred but small clear-cuts may be necessary where all the trees are of a large diameter (Amman et al., 1977).

In young Pinus ponderosa (ponderosa pine) forests (approximately 60-years-old), thinning is an effective means of protecting the stands. Studies in eastern Oregon, USA, show that thinning can reduce tree mortality, caused by the mountain pine beetle, by 90% (Sartwell and Dolph, 1976).

Where possible, the management of forests to encourage mixed species stands (a mosaic of stands of the same species but of different age-classes), will reduce the hazard and overall impact of mountain pine beetle outbreaks.

Chemical Control


The cutting and insecticide spraying of infested trees, or the spraying of infested standing trees, were used for many years to try and control outbreaks. This procedure is no longer recommended because of high costs and the realization that as long as forest conditions are favourable for the development of outbreaks, direct control of infested trees will not reduce losses (Amman et al., 1977).

Mountain pine beetle attacks can be prevented in high-value trees, in developed recreation sites or near homes, by the application of chemical sprays (formulated in water) to the bark. Periodic treatments (annual) will be needed during the course of an outbreak (Amman et al., 1977, 1985). The high cost of this treatment tactic precludes its large-scale use.

Biological Control

Opportunities for enhancing the biological control of the mountain pine beetle may be limited since there is a diverse complex of natural enemies already attacking it (Bellows et al., 1998). Birds such as Picoides spp. (woodpeckers), Contopus spp. (peewees) and Sitta spp. (nuthatches) are useful control agents of the larvae, pupae and adults.

Safranyik et al. (2002) provide a review of the biological control work carried out in Canada. The European bark beetle predators, Thanasimus formicarius and Rhizophagus grandis, were imported and tested in a laboratory. T. formicarius was not released as it is not host specific and thus may upset the balance between the various Canadian bark beetle species, and R. grandis was ineffective. Preliminary trials with Beauveria bassiana were also reviewed.

Mechanical Control

Infested trees have been cut and burned as a means of direct control. However, as is the case with chemicals, as long as forest conditions are favourable for the development of outbreaks, this costly tactic will not significantly reduce losses (Amman et al., 1977).

The exposure of infested logs to solar radiation, by placing them in direct sunlight and covering with clear plastic sheeting, is effective for reducing brood survival (Negrón et al., 2001). This technique is most frequently used in low elevation, P. ponderosa forests.

Pheromonal Control

Pheromones that influence the behaviour of the mountain pine beetle have been identified and synthesized. Trans-verbenol, in combination with the host attractants, alpha-pinene and myrcene, stimulate aggregation and mass-attack. Exo-Brevicomin interrupts aggregation in Pinus monticola (western white pine) but apparently its function is different when the mountain pine beetle attacks P. contorta (Cole and Amman, 1980).

Some treatment effects have been noted when pheromones have been deployed for mass-trapping and the protection of P. monticola forests in Idaho, USA. Work continues to develop their use as an operational tactic for mountain pine beetle pest management. However, their use is not yet wholly effective or economical.

Field Monitoring

Field monitoring consists of aerial and ground surveys, designed to locate groups of dead and dying trees and confirms the presence of mountain pine beetle infestations. These surveys are annually conducted over most forests in western North America.

Integrated Pest Management

The elements of a mountain pine beetle integrated pest management programme include:

- Risk-rating of pine forests, based on site and stand characteristics, to determine their susceptibility to outbreaks.

- Implementation of appropriate cultural practices to reduce outbreak hazard.

- Monitoring of forests to ensure early detection of outbreaks.

- Rapid removal and salvage of infested trees.

- Use of solar radiation to kill beetle broods.

- Preventative spraying of high-value trees.

However, many forests that are susceptible to mountain pine beetle damage are located in remote, inaccessible areas with limited access or have special classifications (e.g. National Park, Monument, Wilderness area, and Wild and scenic river), which preclude forest management. This makes the implementation of pest management programmes logistically difficult, expensive or otherwise unrealistic. Consequently, despite the availability of effective pest management tactics, the mountain pine beetle continues to be a major pest of pine forests in western North America.