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Predicting mountain pine beetle behavior could help save forests

The mountain pine beetle is one of the leading causes of pine tree mortality across North America. For instance, this insect has already killed thousands of acres of pine forests in British Columbia and Alberta, making these areas more vulnerable to wildfires, and turning Canada’s forests into large sources of carbon emissions – resulting from the burned or decaying wood of dead trees – rather than carbon sinks.

Using a groundbreaking approach inspired by fluid mechanics to study the flight performance of the mountain pine beetle, a team of researchers led by the University of Alberta has recently provided a novel method to improve estimates of the insects’ spread through the environment. Better understanding the flight behavior of pine beetles could help conservationists preserve pine forests.

The scientists employed a type of model initially used for idealized airfoils, and showed that it can be successfully applied to various individual animals to predict how factors such as biological sex, age, and body size can impact flight characteristics. 

“We found that there is a dimensionless grouping of velocity and wing beat amplitude that can predict the thrust produced by an insect, and that this grouping can dramatically improve our ability to determine factors that affect flight performance in insects,” said study lead author Zahra Hajati, a mechanical engineer at Alberta.

Using this model on multiple insects –  each with a slightly different wing shape (including some with wing damage), size, and age – the scientists discovered differences by group. For instance, female beetles seemed to have greater flight endurance than males, and younger beetles flew with less thrust than insects from other age groups. 

In order to make the airfoil model functional for pine beetles, the researchers had to modify it to deal with the more complex 3D wings of the insects rather than the simpler, tear-drop shape of idealized airfoils. Interestingly, the main difference between the wings and the idealized airfoils was found to be the relative influence of viscosity, with the insects being more sensitive to it than the airfoils. 

One of the study’s limitations is that the scientists looked at the forces generated by insects over the course of only a few wingbeats. Since, in nature, beetles can fly for hours during dispersal flights, further work is needed to relate the wingbeat-to-wingbeat scaling of force generation and energy consumption to how far the insects can disperse over entire flights.

“This model opens new avenues for entomological investigation, providing a means of dramatically improving statistical confidence levels for insect dispersion studies,” Hajati concluded.

The study is published in the journal Physics of Fluids.

More about the mountain pine beetle 

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 millimeters, about the size of a grain of rice.

These beetles play a significant role in the life cycle of a forest, attacking old or weakened trees, which can help to spur the development of a healthier ecosystem. However, they can also kill large numbers of trees when their populations reach outbreak levels, leading to significant ecological disruption and increasing the risk of forest fires.

The mountain pine beetle has a one-year life cycle in most of its range but can take two years in high-elevation areas where temperatures are lower. Adults emerge from infested trees in the summer, fly to a new host tree, and mate. Females then tunnel into the bark, where they lay their eggs. The larvae feed on the inner bark of the tree, eventually killing it by cutting off its nutrient supply.

Mountain pine beetles infest and kill host trees, usually lodgepole, ponderosa, Scotch and limber pine. In recent decades, warmer temperatures have allowed beetles to survive in areas where cold temperatures previously kept them in check. This has led to an unprecedented epidemic of beetle infestations in North American pine forests, particularly in British Columbia and the Rocky Mountain region of the United States. 

The scale of these infestations and their impact on forest ecosystems, the timber industry, and the risk of forest fires are areas of ongoing research and management efforts.

Future of pine forests

The future of pine forests, especially in regions affected by the mountain pine beetle, depends on a variety of factors including climate change, forest management practices, and ongoing scientific research and innovation.

Climate Change

Warmer temperatures associated with climate change have allowed pests like the mountain pine beetle to expand their range and survive in areas that were previously too cold. 

If global warming continues at its current pace, these pests could continue to spread and cause further damage. On the other hand, more extreme weather events and changes in precipitation could also affect the health and distribution of pine forests.

Forest Management

Forest management practices can also influence the future of pine forests. Proper management can help maintain forest health and resilience, making trees less susceptible to pests and diseases. 

For example, practices like thinning, which reduces tree density, can help improve the overall health of the forest and make it less susceptible to large-scale infestations. Controlled burns can also be used to reduce the risk of catastrophic wildfires and create a more varied and resilient forest landscape.

Scientific Research and Innovation

Research and innovation can also play a crucial role. Scientists are studying the life cycle and behavior of pests like the mountain pine beetle in order to develop more effective control methods. In addition, genetic research could potentially lead to the development of pest-resistant tree varieties.

Natural Regeneration

Even in areas heavily affected by pests or fires, pine forests can often recover naturally over time. Some species of pine have cones that only open and release their seeds during a fire, ensuring a new generation of trees after such an event. 

However, this recovery can take many decades or even centuries, and the resulting forest may be different from the original one due to changes in conditions and species composition.

While challenges exist, there are also many strategies and potential solutions that can help protect and preserve pine forests for the future. The key will be implementing these strategies effectively and continuing to adapt them based on ongoing research and changes in conditions.

By Andrei Ionescu, Staff Writer

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