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Get the forest foliated

Researcher investigates the behavior of local pests and defoliators in Washington

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Washington state hosts some of the most fascinating forests in the country. However, it also provides habitats for pests that feed on trees. These insects, which often cause trees to lose leaves, are known as defoliators. 

To better understand the behavior of pests and defoliators, Alex Pane, a graduate student from the School of Environmental and Forest Sciences, conducted a study on the two major pests in Pacific Northwest: the Douglas-fir beetle and the western spruce budworm. 


Deployment of western spruce budworm pupae and larvae to assess natural enemy communities across the Washington Cascade Mountain Range.

The Douglas-fir beetle is a type of bark beetle that primarily attacks large and mature Douglas-fir trees. It eats the nutritious foam layer under the bark and weakens — even kills — the tree. As a defoliator, the western spruce budworm shares the same host Douglas-fir trees with the beetle. 

“Western spruce budworms generally come out early in spring as larva,” Pane said. “They consume new foliage. In the spring, the bud bursts and emerge new leaves. That tissue is very nutritious and not defended well by the tree. The budworm takes advantage of it.” 

According to Pane, both species affect the growth of trees and harm the health of the ecosystem, ultimately damaging the economic value of the forest. 

As Pane observes and studies the behavior of the two species, he found those insects may exhibit different activity patterns in the east and west Cascades mountain range.

For example, east of the Cascades, western spruce budworms cause a lot of damage that persists for a long period of time. Interestingly, their families on the west side are calm and make little destruction. 

“I am interested in looking at the reason that drives such differences in behaviors,” Pane said. “It might be related to the climate. I am also looking at natural enemy communities. Maybe there is a more robust community on the west that better controls the population of western spruce budworms.” 

In the past summer, Pane worked on collecting data in the field and studied plant and insect communities in Washington state. To find out how spatial and temporal changes influence insect behaviors, Pane also studied the disturbance record of forests in Oregon, Washington, and British Columbia back to the 1960s. 

Historical disturbance events may reflect changes in pest outbreaks over the years. Pane mentioned these changes are possibly driven by climate change. 

According to the United States Department of Agriculture, the warm temperature encourages bark beetles to expand territory and attack susceptible forests. In 2018, the hot, dry summer led to an exceptionally high number of dead Douglas-fir trees in Washington state due to attacks from the Douglas-fir beetles. 


Frass (excrement and debris) from Douglas-fir beetles boring into a Douglas-fir tree.

Pane expects his research results to help to identify regions that are likely attacked by bark beetles and defoliators. Such information will guide management decisions in certain forests and maintain a healthy forest system in Washington state. 

The current challenge is due to the complexity of insect interaction, there is not much good information about how pests interact with each other and how these activities disturb the forest. Pane is also looking into whether the local pest pattern possibly depends on larger regional patterns which are difficult to target and manage. 

“This research is important,” Pane said. “It helps to inform how large-scale processes can influence more local-scale issues.” 

Reach reporter Sunny Wang at Twitter: @sunnyqwang64

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