Tiny Woolly Terrors: The Attack of the Adelgid

By December 20th, 2013 at 10:35 am | Comment 1

If you’re looking for more projects for the holiday season, we’ve got 12 Days of Citizen Science for you!

Don’t forget to check out the public radio segment about Tiny Terrors on WHYY’s The Pulse!

woolly adelgid

Evidence of hemlock woolly adelgid on hemlock

The Grinch is back and this time in the form of a tiny insect invader. Meanwhile, scientists are looking for the one tree… that will save Christmas. Ok, dramatics aside, this is only half wrong. Eastern Hemlock, balsam, and Fraser fir are three evergreen trees that dominate large swaths of terrain across Eastern America dying from the attack of two invasive pests. One, the balsam woolly adelgid or Adelges piceae, has had a devastating impact on Fraser fir and balsam fir, trees you may recognize in your living room if you celebrate Christmas. Eastern hemlock trees dying from the hemlock woolly adelgid, otherwise known as Adelges tsugae, are also leaving behind bald patches on a damaged forest landscape.

The key to preserving our forests? Scientists at North Carolina State University and in the Alliance for Saving Threatened Forests believe that a particular tree or rather some particular groups of trees might be the solution. The idea is that there may be trees within each species that have a natural resistance to the adelgid that most trees in America don’t have.

This is part of the reason why hemlocks and firs are dying in such large numbers. The Balsam woolly adelgid is originally from central Europe and the hemlock woolly adelgid is from East Asia, where native trees have evolved resistance or tolerance to adelgid infestation. But the trees in the U.S.? Dr. Fred Hain, an entomologist at North Carolina State University, says they have had “no co-evolution [with the adelgid] and the trees do not show any resistance and are very susceptible. And also, there are no natural enemies in this system to keep pests under control.”  But there may be trees in our native range are lucky enough to have some form of resistance to the adelgid; we just haven’t found them yet. As it turns out, they’re extremely hard to find. “It’s like looking for a needle in a haystack,” Dr. Hain says.

This is where the Tiny Terrors Project (official site) enters. Led by Dr. Hain and grad student Erin Mester, the Tiny Terrors project is a piece of the Alliance for Saving Threatened Forests that enlists the help of citizen scientists to find those resistant trees. With so much land to cover and so many trees to see, citizen scientists can provide a significant boost to the search for resistant trees. Hain and Mester ask volunteers to try and identify resistance by finding trees that have very few or no adelgid in infested areas. The team will then try to get either a cone, if possible, or clippings from the tree to run experiments on.

The first thing they need to do is determine whether or not the tree has been treated with chemical pesticides, since that would make a tree appear to be resistant even if it actually has no natural resistance. Then, if the tree hasn’t been washed or injected with pesticides, then the scientists will grow seedlings from a cone or try to clone the tree from cuttings and expose it to adelgid to see if it really is resistant. If the adelgid doesn’t take, or if the trees survive the infestation, then it becomes a task of understanding what the cause of resistance is. “So far, we’ve identified a thicker cuticle of the needle as being critical,” Dr. Hain says, meaning the few trees the Tiny Terrors project has pulled up as promising appear have a thicker skin. This makes it more difficult for adelgids to penetrate the tissue. This hypothesis also seems to be supported by the fact that trees native to central Europe and Asia have this adaptation as well.

Hopefully, scientists like Hain and Mester will be able to transfer the resistance genes over to other hemlocks or firs if they’re able to find those special trees. Unfortunately, even this is easier said than done. A similar story played out on the continent in the early 20th century, when a fungal infection called the chestnut blight nearly wiped out the American chestnut. Chinese chestnut varieties had a natural form of resistance to the blight, and scientists tried then to create a viable hybrid between Chinese and American trees to combat the blight. By breeding that hybrid with other surviving American chestnut trees for many generations, scientists were finally able to create a blight-resistant tree that had 98% American genes and 2% Chinese genes. But that wasn’t until nearly seventy years after the blight had decimated the population of chestnuts in America. At this point, much of the original genetic diversity of the American chestnut is gone forever, and it’s unclear whether or not chestnuts will ever return to the full extent of their former distribution.

This could happen for Fraser and Balsam firs as well, should nearly all of the population of trees be killed. Fortunately for hemlocks, however, an organization called Camcore has been stockpiling a bank of hemlock seeds for the purpose of preserving their genetic diversity. But Fraser firs may not be so lucky since not as many people are looking out for them, despite Christmas trees occupying a nearly 1 billion dollar industry.

While none of these trees are important as timber, hemlocks are what is known as a keystone species and have a disproportionate impact on the ecosystem. “The ecological impact,” Dr. Hain says, “could be quite traumatic.” For instance, hemlocks are often found by streams and provide a good deal of shade. This shade might be critical to keeping the water temperature down, which is already reaching the thermal limit for trout in the south. The loss of that shade could also ruin the habitat for trout.

The Tiny Terrors project is just getting on its feet. But, if it’s successful, it could help prevent the deaths of many conifer forests and the life depending on them. That success hinges on a number of things, including whether or not naturally resistant trees exist and if a successful hybrid can be made, but most importantly on how many people volunteer as citizen scientists. Dr. Hain believes that the project will move forward, as more people spread the word.  In any case, Christmas is probably still on this year with a Fraser fir and, who knows, maybe a trout. But in the future, people may have to find alternatives.

To get involved with the Tiny Terrors project, either visit the site through SciStarter’s portal or join on the Alliance for Saving Threatened Forests page.

Image: Wikipedia


Angus R. Chen is a research assistant at Princeton University, where he does geochronology research using uranium and lead isotopes from zircon crystals. Previously, he was a research intern at the Harvard Forest, studying the impacts of climate change on soil. He recently graduated from Oberlin College with a double major in environmental science and creative writing. When he’s not in the lab admiring rocks and then pulverizing them, he writes poetry, fiction, science articles, and makes cool videos.