Mountain pine beetle

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Mountain pine beetle
Dendroctonus ponderosae.jpg
Adult
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Infraorder: Cucujiformia
Family: Curculionidae
Genus: Dendroctonus
Species:
D. ponderosae
Binomial name
Dendroctonus ponderosae
(Hopkins, 1902)

The mountain pine beetle (Dendroctonus ponderosae) is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia. It has a hard black exoskeleton, and measures approximately 5 millimetres (1⁄4 in), about the size of a grain of rice.

Contents

In western North America, an outbreak of the beetle and its microbial associates affected wide areas of lodgepole pine forest, including more than 160,000 km2 (40 million acres) of forest in British Columbia. [1] The outbreak in the Rocky Mountain National Park in Colorado began in 1996 and has caused the destruction of millions of acres/hectares of ponderosa and lodgepole pine trees. At the peak of the outbreak in 2009, over 16,000 km2 (4.0 million acres) were affected. [2] The outbreak then declined due to better environmental conditions and the fact that many vulnerable trees had been already destroyed. [2] [3]

Mountain pine beetles inhabit ponderosa, whitebark, lodgepole, Scots, jack, [4] limber, Rocky Mountain bristlecone, [5] and Great Basin bristlecone [6] pine trees. Normally, these insects play an important role in the life of a forest, attacking old or weakened trees, and speeding development of a younger forest. However, unusually hot, dry summers and mild winters in 2004–2007 throughout the United States and Canada, along with forests filled with mature lodgepole pine, led to an unprecedented epidemic. [7]

The outbreak may have been the largest forest insect blight seen in North America since European colonization. [8] Monocultural replanting, and a century of forest fire suppression have contributed to the size and severity of the outbreak, and the outbreak itself may, with similar infestations, have significant effects on the capability of northern forests to remove greenhouse gases (such as CO2) from the atmosphere. [9]

Because of its impact on forestry, the transcriptome [10] and the genome [11] of the beetle have been sequenced. It was the second beetle genome to be sequenced.

Life cycle

A lodgepole pine tree infested by the mountain pine beetle, with visible pitch tubes Infested tree.jpg
A lodgepole pine tree infested by the mountain pine beetle, with visible pitch tubes

Beetles develop through four stages: egg, larva, pupa and adult. Except for a few days during the summer when adults emerge from brood trees and fly to attack new host trees, all life stages are spent beneath the bark. [12]

In low elevation stands and in warm years, mountain pine beetles require one year to complete a generation. At high elevations, where summers are typically cooler, life cycles may vary from one to two years

Female beetles initiate attacks. As they chew into the inner bark and phloem, pheromones are released, attracting male and female beetles to the same tree. The attacking beetles produce more pheromones, resulting in a mass attack that overcomes the tree's defenses, and results in attacks on adjacent trees.

Natural predators of the mountain pine beetle include certain birds, particularly woodpeckers, and various insects.


Tree infestations

Effects

Mountain pine beetles can damage whole regions of forest.

Mountain pine beetles affect pine trees by laying eggs under the bark. The beetles introduce blue stain fungus into the sapwood that prevents the tree from repelling and killing the attacking beetles with tree pitch flow. The fungus also blocks water and nutrient transport within the tree. On the tree exterior, this results in popcorn-shaped masses of resin, called "pitch tubes", where the beetles have entered. [13] The joint action of larval feeding and fungal colonization kills the host tree within a few weeks of successful attack (the fungus and feeding by the larvae girdles the tree, cutting off the flow of water and nutrients). In recent years, drought conditions have further weakened trees, making them more vulnerable and unable to defend against attack. When the tree is first attacked, it remains green. Usually within a year of attack, the needles will have turned red. This means the tree is dying or dead, and the beetles have moved to another tree. Within three to four years after the attack, very little foliage is left, so the trees appear grey. [7]

As beetle 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 (such as winter lows of -40°) can reduce the beetle populations and slow the spread, but the insects can recover quickly and resume their attack on otherwise healthy forests.

Increases due to climate change

Climate change and the associated changing weather patterns occurring worldwide have a direct effect on biology, population ecology, and the population of eruptive insects, such as the mountain pine beetle. This is because temperature is a factor which determines insect development and population success. [14] Mountain pine beetles are a species native to Western North America. [15] Prior to climatic and temperature changes, the mountain pine beetle predominately lived and attacked lodgepole and ponderosa pine trees at lower elevations, as the higher elevation Rocky Mountains and Cascades were too cold for their survival. [16] Under normal seasonal freezing weather conditions in the lower elevations, the forest ecosystems that pine beetles inhabit are kept in a balance by factors such as tree defense mechanisms, beetle defense mechanisms, and freezing temperatures. It is a simple relationship between a host (the forest), an agent (the beetle) and the environment (the weather and temperature). [15] However, as climate change causes mountain areas to become warmer and drier, pine beetles have more power to infest and destroy the forest ecosystems, such as the whitebark pine forests of the Rocky Mountains. [15]

Increased temperatures also allow the pine beetle to increase their life cycle by 100%: it only takes a single year instead of two for the pine beetle to develop. As the Rockies have not adapted to deal with pine beetle infestations, they lack the defenses to fight the beetles. [15] Warmer weather patterns, drought, and beetle defense mechanisms together dries out sap in pine trees, which is the main mechanism of defense that trees have against the beetle, as it drowns the beetles and their eggs. [15] This makes it easier for the beetle to infest and release chemicals into the tree, luring other beetles in an attempt to overcome the weakened defense system of the pine tree. As a consequence, the host (forest) becomes more vulnerable to the disease-causing agent (the beetle). [15]

Pine forests in British Columbia have been devastated by a pine beetle infestation, which has expanded unhindered since 1998 at least in part due to the lack of severe winters since that time; a few days of extreme cold kill most mountain pine beetles and have kept outbreaks in the past naturally contained. The infestation, which (by November 2008) has killed about half of the province's lodgepole pines (33 million acres or 135,000 km2) [17] [18] is an order of magnitude larger than any previously recorded outbreak. [19] One reason for unprecedented host tree mortality may be due to that the mountain pine beetles have higher reproductive success in lodgepole pine trees growing in areas where the trees have not experienced frequent beetle epidemics, which includes much of the current outbreak area. [20] In 2007 the outbreak spread, via unusually strong winds, over the continental divide to Alberta. An epidemic also started, be it at a lower rate, in 1999 in Colorado, Wyoming, and Montana. The United States forest service predicts that between 2011 and 2013 virtually all 5 million acres (20,000 km2) of Colorado's lodgepole pine trees over five inches (127 mm) in diameter will be lost. [18]

The whitebark forests of the Rockies are not the only forests that have been affected by the mountain pine beetle. Due to temperature changes and wind patterns, the pine beetle has now spread through the Continental Divide of the Rockies and has invaded the fragile boreal forests of Alberta. [15]

Management

Management techniques include harvesting at the leading edges of "green attack", as well as other techniques that can be used to manage infestations on a smaller scale, including: [21]

The US Forest Service tested chitosan, [22] [23] a biopesticide, to pre-arm pine trees to defend themselves against MPB. The US Forest Service results show colloidal chitosan elicited a 40% increase in pine resin (P<0.05) in southern pine trees. One milliliter chitosan per 10 gallons water was applied to the ground area within the drip ring of loblolly pine trees. The application was repeated three times from May through September in 2008. The chitosan was responsible for eliciting natural defense responses of increased resin pitch-outs, with the ability to destroy 37% of the pine beetle eggs. [24] Dr. Jim Linden, Microbiologist, Colorado State University, stated the chitosan increased resin pitch-outs to push the mountain pine beetle out of the tree, preventing the MPB from entering the pine tree and spreading blue stain mold. [25]

Searching out, removing, and destroying the brood in infested trees is the best way to slow the spread of mountain pine beetles; however, it may not protect specific trees. Spraying trees to prevent attack is the most effective way to protect a small number of high-value trees from mountain pine beetles. Carbaryl, permethrin and bifenthrin are registered in the United States for use in the prevention of pine beetle infestations. Carbaryl is considered by the EPA to likely be carcinogenic to humans. It is moderately toxic to wild birds and partially to highly toxic to aquatic organisms. Permethrin is easily metabolized in mammalian livers, so is less dangerous to humans. Birds are also practically not affected by permethrin. Negative effects can be seen in aquatic ecosystems, as well as it being very toxic to beneficial insects. Bifenthrin is moderately dangerous to mammals, including humans; it is slightly more toxic to birds and aquatic ecosystems than permethrin, as well as extremely toxic to beneficial insects. [26]

Fall and burn is the technique being used in Alberta where there is hope of limiting the outbreak to western Canada, preventing its spread to northern Saskatchewan and further towards eastern Canada where jack pine may be vulnerable as far east as Nova Scotia. [27]

Effects

Fire hazard

While weather and drought are important drivers of wildfires in subboreal forests, bottom-up drivers of elevation and vegetation, including the fuel legacies of bark beetle outbreaks, are crucial factors influencing high-severity burning. [28] The outbreak of mountain pine beetles in the early 2010s, ten times larger than previous outbreaks, [29] Huge swaths of central British Columbia (BC) and parts of Alberta have been hit badly, with over 40 million acres (160,000 km2) of BC's forests affected. [30] created dead pine stands representing a potential fire hazard, prompting the BC government to direct fuel management activities in beetle areas as recommended in the 2003 Firestorm Provincial Review. [31]

Previously, cold spells had killed off bark beetles, but with warmer weather they attacked the forests. [32] [33] The longer breeding season is another factor encouraging beetle proliferation. The combination of warmer weather, attack by beetles, and mismanagement during past years has led to a substantial increase in the severity of forest fires in Montana. [33] [34] According to a study done for the U.S. Environmental Protection Agency by the Harvard School of Engineering and Applied Science, portions of Montana will experience a 200% increase in area burned by wildland fires, and an 80% increase in air pollution from those fires. [35] [36]

On the carbon cycle

Researchers from the Canadian Forest Service have studied the relationship between the carbon cycle and forest fires, logging and tree deaths. They concluded by 2020, the pine beetle outbreak will have released 270 megatonnes of carbon dioxide into the atmosphere from Canadian forests. There is yet to be an accepted study of the carbon cycle effect over a future period of time for North American forests, but scientists believe we are at a 'tipping point' of our Western Forests becoming a source of carbon off-put that is greater than that of a 'carbon sink'. [29] Other scientists say that this "tipping point" will reverse itself as new forest life is established. This new growth will remove more carbon dioxide than the mature trees they are replacing would have. According to a 2016 study from the Pacific Institute for Climate Solutions rising levels of carbon dioxide may cancel out the pine beetle impact in British Columbia by 2020. [37] The fertilization effect of the increased CO2 levels has returned BC forests to a carbon sink as of 2016 per Werner Kurz of the Canadian Forest Service. [38]

On water resources

Hydrologists from the University of Colorado have investigated the impacts of beetle-infested forests on the water cycle, in particular, snow accumulation and melt. They concluded that dead forests will accumulate more snowpack as a result of thinner tree canopies and decreased snow sublimation. These thinned canopies also cause faster snowmelt by allowing more sunlight through to the forest floor and lowering the snowpack albedo, as a result of needle litter on the snow surface. [39] Augmented snowpack coupled with dead trees that no longer transpire will likely lead to more available water.

In human culture

In Custer, South Dakota, a giant effigy of a mountain pine beetle is set on fire each winter. [40]

See also

Related Research Articles

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The term bristlecone pine covers three species of pine tree. All three species are long-lived and highly resilient to harsh weather and bad soils. One of the three species, Pinus longaeva, is among the longest-lived life forms on Earth. The oldest of this species is more than 4,800 years old, making it the oldest known individual of any species. Many scientists are curious as to why this tree is able to live so long. In one study, they discovered that Pinus longaeva has higher levels of telomerase activity, which further slows or prevents the attrition rate of telomeres. This potentially contributes to the extended life of the bristlecone pine.

<i>Pinus albicaulis</i> Pine tree species found in North America

Pinus albicaulis, known by the common names whitebark pine, white bark pine, white pine, pitch pine, scrub pine, and creeping pine, is a conifer tree native to the mountains of the western United States and Canada, specifically subalpine areas of the Sierra Nevada, Cascade Range, Pacific Coast Ranges, and Rocky Mountains. It shares the common name "creeping pine" with several other plants.

<i>Pinus contorta</i> Species of plant

Pinus contorta, with the common names lodgepole pine and shore pine, and also known as twisted pine, and contorta pine, is a common tree in western North America. It is common near the ocean shore and in dry montane forests to the subalpine, but is rare in lowland rain forests. Like all pines, it is an evergreen conifer.

<span class="mw-page-title-main">Bark beetle</span> Subfamily of beetles

A bark beetle is the common name for the subfamily of beetles Scolytinae. Previously, this was considered a distinct family (Scolytidae), but is now understood to be a specialized clade of the "true weevil" family (Curculionidae). Although the term "bark beetle" refers to the fact that many species feed in the inner bark (phloem) layer of trees, the subfamily also has many species with other lifestyles, including some that bore into wood, feed in fruit and seeds, or tunnel into herbaceous plants. Well-known species are members of the type genus Scolytus, namely the European elm bark beetle S. multistriatus and the large elm bark beetle S. scolytus, which like the American elm bark beetle Hylurgopinus rufipes, transmit Dutch elm disease fungi (Ophiostoma). The mountain pine beetle Dendroctonus ponderosae, southern pine beetle Dendroctonus frontalis, and their near relatives are major pests of conifer forests in North America. A similarly aggressive species in Europe is the spruce ips Ips typographus. A tiny bark beetle, the coffee berry borer, Hypothenemus hampei is a major pest on coffee plantations around the world.

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<i>Dendroctonus rufipennis</i> Species of beetle

Dendroctonus rufipennis, the spruce beetle, is a species of bark beetle native to British Columbia, Newfoundland and Labrador, Nova Scotia, Ontario, Quebec, Northern Manitoba, the Yukon, Alaska, Colorado, Wyoming, Montana, and Maine. They are known to destroy forests of spruce trees including Engelmann, White, Sitka, and Colorado blue spruce. Adults average 4 to 7 mm in length.

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<i>Ips</i> (beetle) Genus of beetles

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The current bark beetle infestation in the Rocky Mountain region of the United States was first detected in 1996. It involved the Mountain pine beetle, which has since spread across millions of acres of dense forest land. In addition, Spruce beetle populations have also been growing in the area in recent years and are further contributing to the existing outbreak. One of the main factors limiting bark beetle population growth is the temperature they can survive at and climate change has raised the average temperature in the region resulting in warmer winters and hotter, drier summers. This not only sped up the bark beetle reproduction process by providing more time per year for them to complete their developmental stages, moisture stressing due to hotter temperatures also weakens the trees’ defense against attacks by reducing resin production. Furthermore, forest management has also played a significant role as many forests in the region have very dense tree populations which facilitates faster spreading from tree to tree, as well as weakening tree defenses further by stressing them through excessive competition.

References

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  23. ↑ Klepzig, K. (2003). "Cellular response of loblolly pine to wound inoculation with bark beetle-associated fungi and chitosan". Res. Pap. SRS-30.asheville, Nc: U.S. Department of Agriculture, Forest Service, Southern Research Station. 9P. 030.
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  33. 1 2 "Forest Service finds varied beetle activity". The Missoulan. February 14, 2010.
  34. ↑ "UM climate expert says triple-digit Julys will be norm". Billings Gazette. August 27, 2007.
  35. ↑ "Forecast: More air pollution, Study predicts global warming will increase fires in Northern Rockies". Billings Gazette. July 29, 2009.
  36. ↑ Spracklen, D. V; Mickley, L. J; Logan, J. A; Hudman, R. C; Yevich, R; Flannigan, M. D; Westerling, A. L (2009). "Impacts of climate change from 2000 to 2050 on wildfire activity and carbonaceous aerosol concentrations in the western United States" (PDF). Journal of Geophysical Research. 114 (D20): D20301. Bibcode:2009JGRD..11420301S. doi: 10.1029/2008jd010966 .
  37. ↑ "Scientists: Thriving BC forests outpace pine-beetle CO2 losses by 2020" (PDF). Pics.uvic.ca. April 11, 2016. Retrieved 2022-03-23.
  38. ↑ Shore, Randy (April 12, 2016). "Global warming induced 'fertilization effect' causing B.C.'s forests to grow back faster than expected". National Post.
  39. ↑ "Mountain pine beetle activity may impact snow accumulation and melt". ScienceDaily. Retrieved 2014-02-14.
  40. ↑ "'Burn, beetle, burn': giant wooden effigies of invasive pest set on fire in South Dakota". The Daily Telegraph . 22 January 2024. Retrieved 22 January 2024.


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