(Before you watch the new Oregon Field Guide segment (Thursday, Feb. 2) on pine butterfly outbreaks, check out this EarthFix backgrounder from last summer.)
From Burns to Spokane, pine trees have become home to large populations of pine white butterflies this summer. These occurrences have happened decades apart, notably in the 1890s and 1920s, and usually last about two to three years. Washington State University entomology professor Richard Zack says no one’s really sure what causes the population explosion.
“There will be some years when you can’t find one of these butterflies,” Zack says. “And other years, like we’re finding now, where it just seems like they’re flying all over the place.”
Zack says many times –- in large occurrences like these -– pine white butterflies are blown from place to place. And now, unlike previously, they’ve landed in the Tri-Cities, a high desert climate in southeastern Washington — all thanks to urban development.
“I would think in those 1920 outbreaks,” Zack says, “you probably would have had a hard time finding one of those butterflies anywhere in what would have been the Tri-Cities at that time because there would not have been a pine tree.”
Zack says the new-to-the-area butterflies are now here to stay.
Richland Parks and Facilities research manager Tim Warner says the city is developing an urban forestry management plan. He says Richland has planted a little more than 5,000 trees, with more to come. That includes pine trees.
“The idea that there are native trees for our area just isn’t true. Most trees were brought into our region, and the pine is a good example of that. All you have to do is drive a little ways out of the city and find a tree,” Warner says about the naturally treeless landscape.
The butterflies could damage some trees, particularly ponderosa pines. But Zack says damage varies from tree to tree, year to year. It will be apparent as caterpillars feed on needles next spring. But, he says, with pine trees in relatively healthy condition throughout the region, there won’t be many problems.
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