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Mountain pine beetle
Latin name: Dendroctonus ponderosae Hopkins
English name:
Mountain pine beetle
French name:
Dendroctone du pin ponderosa
Order:
Coleoptera
Family:
Curculionidae
Main host(s)
lodgepole pine, pines, ponderosa pine, whitebark pine
Informations on host(s)
Most pine species, including some exotic species, are attacked; however, Jeffrey pine is not a suitable host. In BC, the most common hosts are lodgepole, ponderosa and whitebark pine. Occasionally other species, such as Engelmann spruce (Picea engelmannii), are attacked during outbreaks, but beetle populations do not persist in these occasional hosts. It is highly likely that jack pine is also a suitable host.
Phloeophagus
Micro-habitat(s)
Bark, Trunk
Distribution
Western Canada
Informations on distribution
Present in most parts of British Columbia. In the Prairie Provinces, the mountain pine beetle is currently confined to the foothills of western Alberta, and in southeastern Alberta and southwestern Saskatchewan.
Damage, symptoms and biology
Trees undergoing attack by the mountain pine beetle are first detectable only from the ground, and identification of symptoms requires close examination of trees. Infested trees can be detected through crown and external symptoms, but the mountain pine beetle can only be positively identified (and the success of an attack can only be positively determined) by looking under the bark.
At low (endemic) populations the mountain pine beetle survives in weakened or stressed trees. As populations increase or more trees become stressed because of drought or other causes, the population may quickly increase and spread. Healthy trees are then attacked and huge areas of mature pine stands may be threatened or killed. Warm summers and mild winters play a role in both insect survival and the continuation and intensification of an outbreak. Adverse weather conditions (winter low of -40°C or high winds during dispersal period) can reduce the beetle populations and slow the spread, but the insects can recover quickly and resume their attack on otherwise healthy forests.
The current outbreak is progressing as one might expect, considering the relatively mild winters that have been experienced since the mid 1980s and the generally favourable (to mountain pine beetle development) summer weather patterns. The outbreak is likely to continue until an early cold winter kills overwintering larvae. In fact, it was two back-to-back unseasonably cold fall periods in 1984 and 1985 that caused the collapse of the Cariboo-Chilcotin outbreak. In both of those years, early sustained temperatures in the -30 to -40°C were experienced.
External evidence of beetle infestation on the bole usually consists of (i) pitch tubes on the stem where beetles have entered the tree, and (ii) boring dust at the base of the tree.
Accumulations of pitch or sawdust are conspicuous around entrance holes bored into the bark of trees by adult beetles from mid-July to early September. Sawdust is quickly blown or washed away, but abundant pitch tubes may remain for more than a year after attack. Pitch tubes may be much less evident on trees under severe drought stress prior to attack. During the fall and winter after attack, woodpeckers feed on bark- and wood-boring insects on infested trees. Trunks of trees foraged on by woodpeckers are easily visible as much bark is stripped off and bark fragments accumulate in piles on the ground at the base of trees. Removal of bark from infested trees reveals adult egg galleries, larval feeding galleries, and one or more life stages (eggs, larvae, pupae, adults), depending on the time since attack. Egg galleries are 10–41 cm (average, 28 cm) long, oriented vertically on the stem, and have a short curved or diagonal section at the bottom. Grayish blue staining of sapwood, caused by colonization of ray parenchyma cells by blue stain fungi transmitted by adult beetles, provides a conspicuous symptom shortly after successful attack. Various fungal fruiting structures (such as synnemata and perithecia) and mycelia of blue stain fungi and other fungi are often evident in beetle galleries and pupal chambers.
Tree foliage begins to dry out as soon as the conduction of water up the tree is interrupted. As a result, the colour of the foliage on infested trees gradually changes from bright to dull green. This early symptom in the lower crown will often become visible 2-3 months after attack. However, more distinct colour changes occur during the onset of the growing season the spring following attack. With time, retained foliage colour becomes more dull, and most of the foliage drops in 2-3 years; this will vary from species to species and with weather conditions. These rapid and distinct colour changes are used to schedule aerial mapping of recently attacked trees.
The mountain pine beetle has a life cycle that normally lasts one year. In late summer, the adults emerge from the trees in which they fed and developed and fly off in search of new hosts, into which they bore in search of a partner. The females bore vertical galleries just under the bark, in which they lay their eggs. The larvae that emerge from the eggs spend the winter feeding under the bark. Adult emergence takes place between July and September.
A key stage in the life cycle occurs when the beetle transmits a blue stain fungus to the tree. Attacking beetles carry the spores of the fungus, which gain entry to the tree and eventually overcome its defence system and its ability to withstand beetle attack.
Adults are cylindrical, 3.7 to 7.5 mm long; teneral adults are light creamy tan in colour, changing to black when mature.
Eggs are pearly white, about 1 mm in size, and are laid singly in niches on both sides of the parent gallery.
Larvae are white legless grubs with red-brown heads, about 5 mm long in the fourth (final) instar.
Pupae are white at first, changing to light brown, about 5 mm long, with the external characteristics of the adult beetle visible.
Aerial detection of successfully attacked trees is possible as early as late spring (more typically mid-summer) in the year following attack. The needles of infested trees first turn a faint yellow and then a reddish brown by late summer, which allows easy detection; however, by the time trees prominently display these symptoms, they are often vacated by the mountain pine beetle, which has moved on to attack other trees. Nonetheless, aerial surveys are useful to detect stands where mountain pine beetle activity is probable. Detection of small groups of red-topped trees should be followed with ground inspection to verify cause. If mountain pine beetle is confirmed, ground surveys may be implemented to look for newly attacked trees in the vicinity.
The mountain pine beetle and associated blue stain fungi (Ascomycetes) act together to kill trees. Adults transport spores of the blue stain fungi to new trees within a specialized sac (mycangium) on the maxillary cardine. These fungi are believed to stop water transport in the stem and thus kill infected trees.
Although the mountain pine beetle has many natural enemies including insect predators, parasitoids, and woodpeckers, these do not have sufficient impact on incipient and outbreak populations to exert effective control.
L.S. Unger, NRCan, CFS, Pacific Forestry Centre, Victoria, British Columbia
D.W. Langor, NRCan, CFS, Northern Forestry Centre, Edmonton, Alberta
To learn more:
http://bookstore.cfs.nrcan.gc.ca/detail_e.php?recid=48465
http://bookstore.cfs.nrcan.gc.ca/detail_e.php?catalog=3315
http://mpb.cfs.nrcan.gc.ca/index_e.html
http://cfs.nrcan.gc.ca/subsite/mpb
Forest.forward.moving beyond the pine beetle: http://mpb.cfs.nrcan.gc.ca/index_e.html / Forêts.futur.au-delà du dendroctone : http://mpb.cfs.nrcan.gc.ca/index_f.html
Forest Health Network archives pest data for British Columbia-mountain pine beetle: http://www.pfc.cfs.nrcan.gc.ca/entomology/pests/bc/mpb_e.html / Archives du Réseau sur la santé des forêts concernant les ravageurs en Colombie-Britannique – Dendroctone du pin ponderosa : http://www.pfc.cfs.nrcan.gc.ca/entomology/pests/bc/mpb_f.html
Langor, D.W. 2003. Dendroctone du pin ponderosa. Ressour. nat. Can., Serv. can. for., Cent. for. Nord, Edmonton (Alberta). Dépliant for. 36. http://bookstore.cfs.nrcan.gc.ca/detail_f.php?Catalog=22594 Langor, D.W. 2003. Mountain pine beetle. Nat. Resour. Can., Can. For. Serv., Northern For. Cent., Edmonton, AB. For. Leafl. 36.
http://bookstore.cfs.nrcan.gc.ca/detail_e.php?recid=48465
Mountain pine beetle: http://cfs.nrcan.gc.ca/subsite/mpb/home-accueil / Dendroctone du pin ponderosa : http://scf.rncan.gc.ca/soussite/dpp/home-accueil
Mountain pine beetle effects on stand dynamics: http://cfs.nrcan.gc.ca/subsite/stand/home-accueil / Effets des pullulations du dendroctone du pin ponderosa sur la dynamique des peuplements : http://scf.rncan.gc.ca/soussite/peuplement/home-accueil
Mountain pine beetle predicted overwintering mortality maps: http://cfs.nrcan.gc.ca/subsite/mpb-mortality/home / Cartes de la mortalité hivernale prévue du dendroctone du pin ponderosa : http://scf.rncan.gc.ca/soussite/dpp-mortalite
Régnière, J. 2007. Le dendroctone du pin : penser stratégie. Ressour. nat. Can., Serv. can. for., Cent. for. Laurentides, Québec (Québec). L’Éclaircie Numéro 38. 2 p.
http://bookstore.cfs.nrcan.gc.ca/detail_f.php?catalog=28133
Régnière, J. 2007. Thinking strategically to outsmart the mountain pine beetle. Nat. Resour. Can., Can. For. Serv., Laurentian For. Cent., Quebec, QC. Branching out Number 38. 2 p.
http://bookstore.cfs.nrcan.gc.ca/detail_e.php?catalog=28134
Unger, L.S. 1993. Mountain pine beetle. Revised 2006. For. Can., Pac. For.Cent., Victoria, BC. For. Pest Leafl. 76.
http://bookstore.cfs.nrcan.gc.ca/detail_f.php?recid=34252
Amman, G.D.; McGregor, M.D.; Dolph, R.E. 1985. Mountain pine beetle. U.S. Dep. Agric., For. Serv. Pest Leafl. No. 2, 11 p.
British Columbia Ministry of Forests. 1985. Protection Manual. Vol. II. Pest Management. Chap. 9. Major forest bark beetles, 74 p.
British Columbia Ministry of Forests and Lands. 1987. Mountain pine beetle, a menace to pine forests. PesTopics No. 24, 4 p.
Cole, W.E.; Amman, G.D. 1980. Mountain pine beetle dynamics in lodgepole pine forests. Part I: Course of an infestation. U.S. Dep. Agric., For. Serv. Gen. Tech. Rep. INT-89, 56p.
Cole, W.E.; Amman, G.D. 1983. Mountain pine beetle dynamics in lodgepole pine forests. Part II: Population dynamics. U.S. Dep. Agric., For. Serv. Tech. Rep. INT- 145, 59 p.
McMullen, L.H.; Safranyik, L; Linton, D.A. 1986. Suppression of mountain pine beetle infestations in lodgepole pine forests. Can. For. Serv. Pac. For. Cent. Victoria, BC. Inf. Rep. BCX-276, 20 p.
Moeck, H.A.; Safranyik, L. 1984. Assessment of predator and parasitoid control of bark beetles. Can. For. Serv. Pac. For. Cent. Inf. Victoria, BC. Rep. BC-X-248, 24 p.
Safranyik, L.; Shrimpton, D.M.; Whitney, H.S. 1974. Management of lodgepole pine to reduce losses from the mountain pine beetle. Environ. Can., Can. For. Serv., For. Tech. Rep. No. 1, 24 p.
Shore, T.L.; Safranyik, L. 1992. Susceptibility and risk rating systems for mountain pine beetle in lodgepole pine stands. For. Can. Pac. For. Cent. Victoria, BC. Inf. Rep. BC-X-336, 12 p.
