What is the Mountain Pine Beetle?

A Primer for Teachers & Students
(Words appearing in bold can be found in the glossary)

If you have been following the news in British Columbia and ever-increasingly in Alberta, you may have heard of a very small (usually less than 1 cm long), yet very important insect: the mountain pine beetle. The mountain pine beetle (Dendroctonus ponderosae) is a forest insect found in the southern Rocky Mountains and in areas west of the Continental Divide; however, until recently it had not occurred in the northeastern slopes of the Rocky Mountains.

A photograph of a mountain pine beetle taken from the dorsal view © Canadian Forest Service / 2005

Because it is a bark beetle, the majority of its life cycle is spent under the outer bark of mature pine trees – in British Columbia and Alberta that mostly means lodgepole pine trees (Pinus contorta var. latifolia). Adult female beetles bore into the inner bark called the phloem. They create j-shaped vertical galleries into which eggs are laid. The eggs mature and develop into larvae. The larvae tunnel away from the egg galleries.

A line drawing of a tree with mountain pine beetle galleries inside. The main gallery is along vertical gallery with a j-shaped hook on the end. The small galleries that radiate out laterally from the main gallery are mountain pine beetle larva. © Inside Education / 2005

Usually the larvae over-winter in the tree, develop into pupae and in the summer emerge as adult beetles. They then exit the tree to find another pine tree host, and the cycle continues. The eggs of one beetle can produce enough beetles to colonize 15 more trees!

Generally, the life cycle of the mountain pine beetle is as follows:

A diagram of the life cycle of a mountain pine beetle. The life cycle starts as an Adult laying eggs in August, the eggs then hatch into larva in the fall and stay at that life sage through the winter until they pupate in late June and become an adult in July. © Alberta Sustainable Resource Development / 2005

This cycle is usually one year, but may take two years to complete if conditions are not favourable (e.g. rainy summers, cool summers, high altitudes).

What Role Does it Play in the Forest?

The mountain pine beetle (MPB) prefers mature large pine trees and can kill them within one year of attack. By selecting aging, stressed, large pine trees, the beetle plays a role in helping to renew the forest through a process called succession. Succession is the term used to describe the process by which a forest originates, grows and changes over time. Initially, the dead trees provide food and shelter for other species. Eventually, the nutrients of the trees are broken down and returned to the soil. By removing the larger trees, more light and space are available for young trees to grow.

The MPB is also a food source for some bird, mammal and other insect species. In particular, woodpeckers have adapted to find and eat bark beetles under the bark.

How do Bark Beetles Kill a Tree?

Once a female beetle colonizes a new host tree, she releases pheromones that attract other female and male beetles to the tree – meaning a successful MPB colonization always involves many more than one beetle. The sharp mouthparts of the adult mountain pine beetle are ideally suited for boring through the bark to make the long, vertical galleries where the eggs are laid. It is also those mouthparts that carry blue stain fungus (their body carries it too). Blue stain fungal spores clog up the tree’s water-conducting vessels, or xylem.

In addition, the larvae cause even more direct feeding damage than the adults. They tunnel horizontal galleries around the tree. These galleries girdle the tree and disrupt the phloem layer. The phloem is important because it transports nutrients throughout the tree. By disrupting both the xylem and phloem of pine trees, the MPB larvae and their accompanying blue stain fungus make a deadly combination. The girdling of the tree and cutting off nutrient flow in the phloem layer is what causes the tree to die so quickly – within one year of colonization, in most cases.

A cross section of a pine tree showing the heartwood in the middle, sapwood (xylem) as the next concentric circle or ring, cambium as the next ring, inner bark or phloem as the next ring, and finally the outer ring is the outer bark. © Inside Education / 2005

Signs and Symptoms

If you suspect mountain pine beetle colonization, look for the following signs and symptoms:

Outside the Tree

• Yellowish-green to reddish-brown needles throughout the crown of the attacked pine. Depending on the time of year, the needles will turn from green to red within a year of colonization. Usually once the needles turn red, the tree is dying or dead and the majority of the beetles have moved to another tree.
• Cream coloured resin (pitch) that looks like crystallized honey oozing out of beetle entry holes (pitch tubes) on the tree trunk. The tree’s natural defense against the MPB is to try to “pitch” the beetle out of the tree by a flow of sap or pitch. Sometimes the tree can successfully get rid of the beetles before the gallery is completed and before major damage has occurred. These trees will not usually die.
• Round exit holes where the adult beetles have left the tree the following year will also be evident boring sawdust found in bark crevices and around the base of the tree
• An abundance of woodpecker evidence (flaked off bark, especially) can also indicate a colonized tree

Under the Outer Bark

• Egg galleries (j-shaped and up to 41 cm long) under the bark, beginning above the entrance holes and running along the grain of the wood
• Larval galleries girdling around the tree
• Presence of eggs, larvae, pupae and/or beetles
• Greyish blue sapwood caused by blue stain fungi carried by the beetles

So What Has Changed?

Normally, MPB populations are kept in check by natural factors such as predators, parasites, wet summers, and early, cold winters (-30ºC or lower in November) or late, cold springs. (Mountain pine beetle larvae survive cold winters by producing an insect antifreeze called glycerol.) The harsh weather conditions are the most effective in controlling the population. Forest fires also control MPB populations because they often eliminate large numbers of available host trees and, if hot enough, can kill beetles under the bark.

The limiting or prevention of forest fires on the landscape has resulted in large continuous areas of mature pine trees that are older than 80 years – the MPB’s favourite habitat. (However, the beetles are also starting to colonize younger and smaller pine trees.) This has resulted in large-scale MPB outbreaks in British Columbia and an ever-increasing risk in Alberta. Because many of British Columbia and Alberta’s lodgepole pine forests are of this age, this insect can be a serious threat to the biodiversity of forests.

Another recent contributing factor is the general warming climate trend. Since the winters are not getting cold enough to kill the beetle, it is able to survive the winter and continue to reproduce. This has also allowed it to expand its range further north and east than its historical distribution. There is also an added risk that the mountain pine beetle could adapt to jack pine trees. This could result in the mountain pine beetle eventually moving east across Canada.

From a human perspective, there is a also a greater reliance than ever before on the forest to meet a variety of economic and social needs. The widespread MPB outbreak in British Columbia has had significant economic and social impacts on the forest products industry (B.C.’s largest industry), communities and tourism. Loss of income, resources and jobs are a result of the growing issue of MPB outbreaks.

What Can be Done?

There are no easy answers to this question!

Forest management to deal with the spread of the MPB is not a simple task. Managing the beetle has proven to be difficult in B.C. where the insect has affected over 7 million hectares of pine forest. In addition to the large size of the area affected, many different land objectives and land managers are involved. This requires careful but timely consideration.

In Alberta, there are two main approaches to mountain pine beetle control: a short-term strategy that focuses on the beetle and a long-term one that focuses on beetle-susceptible pine stands.

The beetle is difficult to control. It is protected under the bark most of its life and the tree dies quickly after being colonized. Chemicals in general do not work because they usually end up damaging the tree and affecting other species that use the tree.

Therefore, the beetle strategy focuses on limiting the spread of the infestation before it reaches outbreak levels and containing the population when it becomes an outbreak. This strategy requires prevention, monitoring for early detection, and quick control of infestations when the populations are small. To reduce the risk of mountain pine beetle-colonized logs being moved from an infested area to a new area, Alberta restricts the transportation of pine logs with bark attached, especially during the summer beetle flight. This includes firewood!

Ground and aerial surveys are used to monitor MPB populations. Detection is difficult because the main identifying characteristic of a MPB-infested tree — red needles — is good evidence to find out where the mountain pine beetles were, not where they are, and even more difficult, where they are going.

A map of British Columbia and Alberta that shows the mountain pine beetle range and the area of major outbreak in interior of British Columbia. © Canadian Forest Service / 2005

The control usually involves removal of colonized trees by either prescribed burning or cutting down trees soon after detection before the adults leave to find new trees. The cut trees are then destroyed by burning, peeling off the all the bark or processing them. Once the population reaches high levels (outbreak), pheromone baits can be used to attract and contain the beetles in a given area designated for future tree removal. Individual tree removal also continues on the edges of the infestation to prevent spread.

The long-term strategy involves reducing future threats of mountain pine beetle outbreaks by carefully planning to replace highly susceptible contiguous mature lodgepole pine stands with less susceptible stands of mixed species and age classes. These stands will then be more resilient to insect outbreaks, less susceptible to large wild fires and have improved wildlife habitat. The approaches to create a more diverse forest would include: prescribed burning, reduction of MPB-susceptible host trees and harvesting of stands (earlier than normal) to reduce the available host trees for beetles. Replanting with species other than pine, where possible, could also be implemented.

Summary

It is important to keep in mind that the mountain pine beetle is native to B.C. and some parts of Alberta and does have a role to play in a healthy forest. But things have changed. A general climate warming trend and years of fire suppression have created large areas of good beetle habitat, which has been favourable for its expansion. This is a grave concern as society increases its reliance and places higher values on the forest to meet a variety of social, economic and environmental needs. To help address this large and complex issue an interprovincial/ inter-agency working group was formed.

The Mountain Pine Beetle Strategic Direction Council consists of Natural Resources Canada’s Canadian Forest Service, Parks Canada, Alberta Sustainable Resource Development, Alberta Community Development, forest industry representatives (Hinton Wood Products and Spray Lake Sawmills), B.C. Ministry of Forests and Range and B.C. Parks. This group shares the same objective of minimizing the impact of the eastern and northern expansion of the mountain pine beetle. It works collaboratively to protect the economic values of the provincial and working forests and to achieve the ecological objectives of national and provincial parks and protected areas.