Bark beetles in double-time

 

Bark beetles have always been part of Western forests, cycling from massive outbreaks into periods of low activity. But the current beetle outbreak is unprecedented – it has killed 30 million acres of lodgepole, ponderosa, jack pine and whitebark so far, in a swath from New Mexico up into Canada and even Alaska.

Now, scientists are finding that the immense destruction is being helped along by climate change. Warming temperatures mean that bark beetles mature from egg to tree-trashing adult in one year instead of two, and even produce eggs for a second generation.

The findings bear out predictions described in our 2004 story "Global Warming's Unlikely Harbingers", by High Country News contributing editor Michelle Nijhuis. That feature explained how years earlier, Jesse Logan, research entomologist for the Forest Service’s Rocky Mountain Research Station, and fellow scientists had begun wondering how global warming might affect beetle outbreaks, and had plugged various temperature increases into a computer model:

When temperatures hit two degrees Celsius higher than the average conditions at one of their whitebark pine study sites, prospects for the beetles improved dramatically. Beetles raced through a one-year life cycle at higher elevations. They also synchronized their emergence, allowing them to join forces and overwhelm tree defenses. High-mountain mass attack — and mass tree death — suddenly became possible.

"If Logan’s model is correct, even a few uninterrupted years of these widespread, unusually high temperatures will unleash the bark beetle as never before," wrote Nijhuis. Real-world observations seemed to bear out those predictions. Researchers in locations from southeast Idaho to Montana noticed that as temperatures warmed,  the beetles' lifecycle accelerated from two years to just one.

And now, other scientists have confirmed those anecdotal observations, further validating  Logan's model. Jeffry Mitton and Scott Ferrenberg of the department of ecology and evolutionary biology at the University of Colorado-Boulder have proved that pine beetles are breeding not once but twice per year, which could result in "up to 60 times as many beetles attacking trees in any given year," according to a press release describing their work. Their paper will appear in May in The American Naturalist.

Science Magazine describes how the researchers first became aware of the beetle's changed lifecycle:

Four years ago, Mitton and his graduate student Scott Ferrenberg discovered a possible explanation for this epidemic—almost by accident. While hiking in mid-June to survey pines along Niwot Ridge, due east of Boulder, they saw something strange: adult beetles out and flying. Many even landed on the researchers' clothing. The insects, Mitton says, were swarming close to 2 months too early that year. It seemed so implausible that when he told colleagues about the encounter, some didn't believe him. "This would really upset the apple cart," Milton remembers thinking.

So he and Ferrenberg spent the summers of 2009 and 2010 tracking the growth of pine beetles. They even cut observation windows into the bark of dead pine trees so they could look at larvae hiding in their nests. At first, the insects seemed to be developing as normal. But then, the beetles did the unexpected—they morphed into adults and, beginning in mid-June or even earlier, escaped from their trees. The cue for this early flight seemed to be unseasonably hot weather.

But the beetles weren't just bursting out early, Mitton adds. June-emerging bugs attacked nearby pines almost immediately, laying their own eggs. Those offspring developed speedily, becoming adults, by August or September, just in time to infest another round of pine trees—the second that season. Many Colorado beetles, then, have been able to fit a whole new generation—and an untold number of extra young—into their summers, the team found.

Logan, now retired, describes Mitton's and Ferrenberg's paper in an e-mail as "the first verifiable data for within-season completion of a full lifecycle." Logan notes that further study will be needed to figure out if that second generation of larvae survives through the winter, although the warming climate is making such seasonal mortality less likely. But, he says, "this (work) is the real deal and a significant contribution."

The author is High Country News's managing editor.

Image of mountain pine beetle courtesy U.S. Forest Service.

High Country News Classifieds
  • EXECUTIVE ASSISTANT WITH WESTERN RESOURCE ADVOCATES
    Western Resource Advocates (WRA) seeks an enthusiastic and organized problem solver to join our growing team as an Executive Assistant. The Executive Assistant is instrumental...
  • CONSERVATION PROJECT MANAGER
    Great Land Trust seeks to hire a Conservation Project Manager. Position is full-time, based in Anchorage, Alaska. First review of applications will be on October...
  • EXECUTIVE DIRECTOR
    Eagle Valley Land Trust Executive Director Position Description Summary of Position: The Executive Director, working with and reporting to the Board of Directors, has overall...
  • FINANCE & LOGISTICS COORDINATOR
    The Rocky Mountain Biological Laboratory, founded in 1928 as an independent nonprofit organization, is a biological field station located near Crested Butte, Colorado. Our primary...
  • DEVELOPMENT DIRECTOR
    See Full Job Description
  • DEVELOPMENT COORDINATOR
    Position: Development Coordinator Responsible to: Executive Director Time Commitment: 15-20 hours per week, or as otherwise agreed upon General Description: The Development Coordinator assists the...
  • EDUCATION CENTER MANAGER
    Friends of Cedar Mesa seeks a full-time Education Manager for the Bears Ears Education Center to provide day to day operational and administrative oversight. See...
  • TROUT UNLIMITED SCP SOUTHWEST REGIONAL DIRECTOR
    Seeking to hire an experienced advocate/manager to oversee the organization's sportsmen/women-driven advocacy in Colorado, New Mexico and Arizona. Open until filled
  • PROGRAM MANAGER
    for northern AZ collaborative conservation ranchlands group
  • AMAZING PROGRAM DIRECTOR
    If you're an amazing Program or Education Manager looking for an exciting and fulfilling position with an organization that makes a difference in the community,...
  • EXECUTIVE DIRECTOR
    Partners are seeking an experienced and energetic Executive Director who is excited about the opportunity to lead our growing organization! A full description of the...
  • EXECUTIVE DIRECTOR
    High Country News Seeks an Executive Director to advance its mission, grow its audience and influence, and strategically and sustainably guide the organization through a...
  • 2 PROPERTIES ON THE WESTERN EDGE OF THE GILA WILDERNESS
    Organic farm, hot springs, San Francisco River runs through both. [email protected]
  • CHUCK BURR'S CULTUREQUAKE.COM BLOG
    Change will happen when we see a new way of living. Thinking to save the world.
  • SOCIETY FOR WILDERNESS STEWARDSHIP BOARD MEMBER
    Join the SWS board and help us broaden, diversify, and engage the wilderness community.
  • NEW MEXICO BIRDER'S PARADISE.
    Fully furnished 2B/2B home near Bosque del Apache NWR, great for nature lovers.
  • COMING TO TUCSON?
    Popular vacation house, furnished, 2 bed/1 bath, yard, dog-friendly. Lee at [email protected] or 520-791-9246.
  • DIRECTOR, TEXAS WATER PROGRAMS
    The National Wildlife Federation seeks a Director to lead our water-related policy and program work in Texas, with a primary focus on NWF's signature Texas...
  • SPLIT CREEK RANCH
    Spectacular country home on 48 acres with Wallowa River running through it! 541-398-1148 www.RubyPeakRealty.com
  • PERU: WEAVING WORDS & WOMEN ADVENTURE
    April 2020. A 13-day women-only immersion into the culture of Peru led by Page Lambert and True Nature Journeys. Includes Machu Picchu. Graduate credit available...