Mountain pine beetle

Figure 1. Dead trees after mountain pine beetle infestation. Note that all the trees that aren't green are affected, as the pilot who took the picture said: "If it's red, it's dead".

The mountain pine beetle is an insect that has long lived in North American forests. Once a vital part of the ecosystem, the mountain pine beetle would feed on the bark of dying trees and then die out in the winter.

Life Cycle

Depending on yearly temperatures, the average life span for a pine beetle is approximately one year. The larvae typically live under the tree bark during the winter and emerge in the summer as adults. To colonize a tree, the female pine beetle will release a chemical that attracts more beetles to the tree thus colonizing it and eventually killing it. A healthy tree can defend itself by secreting toxic resin and overcoming a small population of beetle, yet a weak tree that may have already been attacked by another insect or group of beetle can also prove a bad host for a colony as it won't provide the nutrients and moisture needed. One sign of a dying tree due to colonization is color change, if the tree is slowly growing yellow, orange, red, and finally brown; it has lost its battle against the pine beetle. Figure 1 shows this tree discolouration, and Figure 2 is what a mountain pine beetle looks like.

Infestation

Figure 2. Mountain pine beetle, an individual beetle is roughly the size of a grain of rice (5 mm).

Since the early 1990’s, rising temperatures due to global warming in Canada have prevented the pine beetle from dying out in the winter. This climate change allows them to continue to feed on trees throughout the year. To sustain a healthy ecology, the temperatures in the winter must be below -35°C for several continuous days to kill off a substantial population of beetle. This is causing some major issues in Canada, and British Columbia in particular, where the insect has wiped out over 50% of the overall pine population since the early 1990’s (see Figure 1). Since the epidemic started, it is estimated that the mountain pine beetle has destroyed over 710 million cubic meters of B.C forests. Figure 3 below shows a graph of defoliated area (in hectares) in Canada as a result of mountain pine beetles from 1990 to 2023.

Figure 3. Defoliated area in Canada by mountain pine beetles 1990-2023.

Spread

There are multiple factors that support the spread of the pine beetle infestation. The biggest impacts come from the increase in temperatures and the how effectively the beetles spread.

• If temperatures keep rising, warmer winters mean a longer life span for the beetles. This means the pine beetle spreads exponentially.
• The adult mountain pine beetle can fly 100 km and one beetle can start a colony on a tree. This causes the overall dispersal of the pine beetle to grow.

Solutions

Many solutions were proposed to slow the epidemic. Reforestation holds large potential, however planting new trees would only give more ground for the beetle to spread. Another proposed solution is to burn the infested trees and removing any other trees that have already been damaged. Today, efforts to control mountain pine beetle outbreaks have been successful in reducing populations and slowing spread.

For Further Reading

• Ecosystem
• Climate change
• Temperature
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