Dendroctonus ponderosae
(black hills beetle)

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Identity

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Preferred Scientific Name

• Dendroctonus ponderosae Hopkins, 1902

Preferred Common Name

• black hills beetle

Other Scientific Names

• Dendroctonus monticolae Hopkins, 1905

International Common Names

• English: beetle, black hills; beetle, mountain pine; mountain pine beetle
• French: dendroctone du pin argente; dendroctone du pin ponderosa

Local Common Names

• Germany: ponderosa riesenbastkaefer; riesenbastkaefer, ponderosa

EPPO code

• DENCPO (Dendroctonus ponderosae)

Summary of Invasiveness

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

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Coleoptera
•                         Family: Scolytidae
•                             Genus: Dendroctonus
•                                 Species: Dendroctonus ponderosae

Notes on Taxonomy and Nomenclature

Top of page D. ponderosae was described from specimens collected from Pinus ponderosa (ponderosa pine) by AD Hopkins in western South Dakota, USA, in 1902. Three years later, Hopkins described a second species, Dendroctonus monticolae, from specimens collected from Pinus monticola (western white pine) in Idaho, USA. Wood (1963) combined D. ponderosae, D. monticolae and Dendroctonus jeffreyi under a single species, D. ponderosae. D. jeffreyi was again recognized as a distinct species based on work by Lanier and Wood (1968).

Description

Top of page Eggs

Scolytidae eggs are smooth, ovoid, white and translucent. The eggs of the mountain pine beetle are approximately 1.02 mm long and laid separately in niches along the egg gallery, which is tightly packed with frass.

Larvae

All Scolytidae larvae are similar in appearance and difficult to separate. They are white, 'C'-shaped and legless. The head capsule is lightly sclerotized and amber, with dark, well-developed mouthparts. Each abdominal segment has two to three tergal folds and the pleuron is not longitudinally divided. The larvae do not change as they grow. There are four larval instars and mature larvae are 4-6 mm long.

Pupae

Scolytid pupae are white and mummy-like. They are exarate, with legs and wings free from the body. Some species have paired abdominal urogomphi. The elytra are either rugose or smooth, sometimes with a prominent head and thoracic tubercles.

Adults

The adults range from 3.5 to 6.8 mm long (average of 5.5 mm) and are dark brown to black when mature. They are stout and cylindrical. There are small, deep punctures on the pronotum. The immature (callow) adults are light brown (Wood, 1982; Amman and Cole, 1983).

Distribution

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

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Risk of Introduction

Top of page 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).

Habitat

Top of page 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.

Hosts/Species Affected

Top of page 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).

Host Plants and Other Plants Affected

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Growth Stages

Top of page Vegetative growing stage

Symptoms

Top of page Trees attacked by the mountain pine beetle are usually killed by a single generation of beetles. Therefore, the first evidence of an infestation is the occurrence of groups of trees with yellowish-green, sorrel or red (fading) foliage. The needles on successfully infested trees begin to fade and change colour, from several months to a year after the trees have been attacked. Fading of the foliage usually begins in the lower crown and progresses upwards. One exception is in the case of Pinus lambertiana (sugar pine), where initial attacks often occur in the upper crown. Therefore, fading of the foliage in the upper crown is usually the first evidence of an infestation.

A closer examination of infested trees usually reveals the presence of pitch tubes and/or reddish boring dust on the bark surface. During periods of severe drought, only boring dust may be present. Woodpeckers, in search of larvae and pupae, may also remove portions of the bark of infested trees.

Removal of the bark reveals the characteristic vertical, frass-packed egg galleries, larval feeding galleries and pupal cell. The blue stain fungus, Ceratocystis minor [Ophiostoma minor], discolours the sapwood (Amman et al., 1985).

List of Symptoms/Signs

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Biology and Ecology

Top of page 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).

Natural enemies

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Notes on Natural Enemies

Top of page 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).

Plant Trade

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Wood Packaging

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Impact

Top of page The mountain pine beetle kills trees and is considered to be the most destructive of all bark beetles indigenous to western North America. Group-killing, often involving hundreds of trees, occurs in both mature forests and young, overstocked stands. In Pinus contorta (lodgepole pine) forests, a cumulative tree mortality of 85% can occur during the course of an outbreak. However, the winter survival of the mountain pine beetle broods, at elevations above 2400 m, is usually low, which reduces the probability of outbreaks (Cole and Amman, 1980).

The mountain pine beetle has been at outbreak levels in western North America ever since foresters and forest entomologists have been monitoring damaging pests. A massive outbreak of this insect in Pinus ponderosa (ponderosa pine) forests in the Black Hills of South Dakota, USA, first called the extensive killing by bark beetles in the West to public attention. Other noteworthy outbreaks occurred in northern Arizona, USA, between 1917 and 1926 and in Idaho and western Montana, USA, between 1925 and 1935. Pinus monticola (western white pine) forests in Idaho, and Pinus lambertiana (sugar pine) forests in California, USA, have repeatedly suffered heavy losses due to this insect (Furniss and Carolin, 1977). Since 1979, major outbreaks have occurred in portions of California, Colorado, Idaho, Montana, Oregon, South Dakota, Utah, Washington and Wyoming, USA (Ciesla and Coulston, 2002). An outbreak in P. contorta forests in north-central British Columbia, Canada, began in 1994. Several successive years of mild winter temperatures have resulted in an increased brood survival. This outbreak is considered to be Canada's largest forest-insect outbreak (Routledge, 2002).

Forest conditions that favour the development of mountain pine beetle outbreaks are well understood. In P. ponderosa forests, overstocked stands, that are slow in growth, are subjected to mountain pine beetle attacks. In P. contorta forests, older stands with a large proportion of trees that have large diameters (>25 cm) and thick phloems, provide favourable conditions for the development of outbreaks (Cole and Amman, 1980).

Environmental Impact

Top of page During outbreaks, widespread tree mortality alters the forest ecosystem. In some cases, pines have been replaced by less desirable species. Occasionally, forested areas are converted to grass and shrubs. The profusion of beetle-killed trees can alter the distribution and abundance of wildlife species, by changing the thermal and hiding cover. Following an infestation, tree mortality may increase the water yield for several years. Moreover, dead trees that remain in the aftermath of an outbreak, are sources of fuels and can result in wildfires of increased extent and intensity (Amman et al., 1985).

Detection and Inspection

Top of page 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.

Similarities to Other Species/Conditions

Top of page 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.

Prevention and Control

Top of page 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.

References

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Amman GD; Cole WE, 1983. Mountain pine beetle dynamics in lodgepole pine forests. Part II: Population dynamics. General Technical Report, Intermountain Forest and Range Experiment Station, USDA Forest Service, No. INT-145:v + 59 pp.

Amman GD; McGregor MD; Cahill DB; Klein WH, 1977. Guidelines for reducing losses of lodgepole pine to the mountain pine beetle in unmanaged stands in the Rocky Mountains. General Technical Report, United States Department of Agriculture Forest Service, INT-36:[2+] 20 pp.

Amman GD; McGregor MD; Dolph RE Jr, 1985. Mountain pine beetle. Forest Insect and Disease Leaflet, USDA Forest Service, No. 2:11 pp.

Bellows TS; Meisenbacher C; Reardon RC, 1998. Biological control of arthropod forest pests of the Western United States: a review and recommendations, 121 pp.

CABI/EPPO, 1998. Distribution maps of quarantine pests for Europe (edited by Smith IM, Charles LMF). Wallingford, UK: CAB International, xviii + 768 pp.

CABI/EPPO, 2002. Dendroctonus ponderosae. Distribution Maps of Plant Pests, No. 635. Wallingford, UK: CAB International.

Cibrián Tovar D; Méndez Montiel JT; Campos Bolaños R; Yates III HO; Flores Lara JE, 1995. Forest Insects of Mexico. Chapingo, México: Universidad Autonoma Chapingo. Subsecretaria Forestal y de Fauna Silvestre de la Secretaria de Agricultura y Recursos Hidraulicos, México. United States Department of Agriculture, Forest Service, USA. Natural Resources Canada, Canada. North American Forestry Commission, FAO, Publication 6.

Ciesla WM; Coulston J, 2002. Report of the United States on the criteria and indicators for sustainable management of temperate and boreal forests of the United States, Criterion 3 - Maintenance of ecosystem health and vitality, Indicator 15, Area and percent of forest affected by processes or agents beyond the range of historic variation. USDA Forest Service, On line: http://www.fs.fed.us/research/sustain/.

Cole WE; Amman GD, 1980. Mountain pine beetle dynamics in lodgepole pine forests. Part 1: Course of an infestation. General Technical Report, Forest Service, United States Department of Agriculture, INT-89:[3] + 56 pp.

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

Furniss RL; Carolin VM, 1977. Western Forest Insects. Washington DC, USA: US Department of Agriculture Forest Service, Miscellaneous Publication No. 1339.

Jarvis DS; Kulakowski D, 2015. Long-term history and synchrony of mountain pine beetle outbreaks in lodgepole pine forests. Journal of Biogeography, 42(6):1029-1039. http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2699

Lanier GN; Wood DL, 1968. Controlled mating, karyology, morphology and sex ratio in the Dendroctonus ponderosae complex. Annals of the Entomological Society of America, 61:517-526.

Negrón JF; Shepperd WD; Mata SA; Popp JB; Asherin LA; Schoettle AW; Schmid JM; Leatherman DA, 2001. Solar treatments for reducing survival of mountain pine beetle in infested ponderosa and lodgepole pine logs. USDA Forest Service, Rocky Mountain Research Station, RP-30.

Routledge DA, 2002. BC's west central mountain pine beetle epidemic. Canadian Silviculture, Winter 2002 issue.

Safranyik L; Shore TL; Moeck HA; Whitney HS, 2002. Dendroctonus ponderosae Hopkins, mountain pine beetle (Coleoptera: Scolytidae) In: Mason PG, Huber JT, eds. Biological control programmes in Canada, 1981-2000. Wallingford, UK: CAB International, 104-109.

Sartwell C; Dolph RE, 1976. Silvicultural and direct control of mountain pine beetle in second growth ponderosa pine. USDA Forest Service, Pacific Northwest Forest and Range Experiment Station, Research Note PNW-268.

Sun J; Gillette NE; Miao Z; Kang L; Zhang Z; Owen DR; Stein JD, 2003. Verbenone interrupts attraction to host volatiles and reduces attack on Pinus tabuliformis (Pinaceae) by Dendroctonus valens (Coleoptera: Scolytidae) in the People's Republic of China. Canadian Entomologist, 135(5):721-732.

Wood SL, 1963. A revision of the bark beetle genus Dendroctonus Erichson (Coleoptera: Scolytidae). The Great Basin Naturalist, 23:1-117.

Wood SL, 1982. The bark and ambrosia beetles of North and Central America (Coleoptera: Scolytidae), a taxonomic monograph. Great Basin Naturalist Memoirs, No. 6:1359 pp.

Distribution Maps

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