Unfortunately, yes. But this time it’s not feeding on hemlocks. Instead this one prefers true fir trees, and it's called the Balsam Wooly Adelgid (Adelges piceae). It is a native of Europe, where it feeds on the Silver Fir, and was introduced to eastern North America in the early 1900s. It is believed to have traveled to states on the west coast by the late 1920s and into the southeastern United States by the 1950s.
What is a "true fir" you ask? If you'll allow me to take a rabbit trail here, I'll explain it. A true fir is any tree in the genus Abies (family Pinaceae). These trees are all evergreen and have needle-like leaves and cones that stand upright on the limbs where they stay until late summer. They also tend to have more or less the typical Christmas tree shape and tend to grow in mountainous regions. There are 48 to 55 true fir species across North and Central America, Europe, Asia, and North Africa.
One of the more common firs many people are familiar with is the Balsam Fir (Abies balsamea) which is a common choice as a Christmas tree.
Another common Christmas tree is the Fraser Fir (Abies fraseri). Unfortunately, this appears to be one of the trees most seriously impacted by this particular adelgid and will typically die off after only a few years of infestations.
And yet another common Christmas tree is the Noble Fir (Abies procera). I could go on, but you get where I'm going here.
On the west coast, this adelgid tends to prefer Subalpine Fir (Abies lasiocarpa), Pacific Silver Fir (Abies amabilis), and Grand Fir (Abies grandis).
In addition to the ecological devastation an insect infestation can have, it can also have massive economic impacts as well. And in the case of the Balsam Wooly Adelgid, this tiny little bug can even impact your choice of which Christmas tree you might be able to bring into your home.
Before we talk more about the adelgid itself, allow me to get on my soapbox about invasive species. Remember back to the beginning when I mentioned that this adelgid is from Europe and feeds on Silver Firs? Well, as is typically the case with invasive species, where it exists naturally it has natural predators that keep their populations in check, but when they invade a new area, there are no natural predators, so the population can explode and grow out of control.
In the case of invasive adelgids, the trees the impact don't often die in the first season, but their resistance is worn down over several seasons, and some trees are affected at a faster rate than others. The picture below is of dieback that has occurred in Utah as the result of this adelgid.
If enough trees are fortunate enough to survive the invasion then they may be able to develop a natural resistance over time and eventually co-exist with the adelgid, but the problem is that doesn't typically happen. What usually happens is that the insects become too numerous, and cause too much damage, that the tree doesn't have a chance and dies off before they can begin to develop any real resistance.
How can you recognize it?
The Balsam Wooly Adelgid is a small, soft-bodied insect that first appears as a small, white, wooly spot on true fir trees. They are small and hard to find, and are usually on the tree for several months before damage begins to appear. They typically cause something called "gouting" on the trees. The USDA describes gouting as "swollen, deformed branches and persistent woody swellings at branch nodes and terminal buds, and bark calluses." The result? Before the trees actually die, their growth and appearance are affected, which means that trees that were slated for commercial use are no longer marketable. Below is a picture of swollen tissue in the twigs of a tree.
There are four stages in the lifecycle of the Balsam Wooly Adelgid: egg, crawler, stationary immature, and adult. The entire population of these adelgids in the U.S. are female. Females are capable of reproducing without males, and each one can produce as many as 200 eggs that are exact genetic copies of the adult. When the egg first hatches, the emerging young are referred to as crawlers, and these are the only locomotive forms of this adelgid. They can move on their own throughout the tree or can be carried for longer distances via wind or animal dispersal.
Once the crawler finds a good spot to feed, they insert their mouthparts into the bark and never move again. Their first winter is spent dormant on the tree as the stationary immature form. In the spring, the immature adelgid begins feeding again and goes through several molt cycles as it transforms into an adult. In some areas there are two lifecycles per year and where this occurs, adult populations peak in both the spring and fall months.
The adults are small (about 1mm in length), dark purple to black, nearly round, and wingless. It is the adult that produces the waxy, wooly substance that serves to protect both the adult and her eggs until they can mature.
Here is a picture of the underside of a female Balsam Wooly Adelgid. Note the stylet that is pointed out in this image. The adelgid uses this feeding tube to puncture the bark and feed off the tree itself.
Once the stylet is inserted, the adelgid injects a substance into the tree that causes abnormal wood growth and interferes with the proper transport of nutrients and water in the tree.
The initial infestations typically cause the most destruction as the adelgids have encountered a new supply of susceptible trees. Because all the adelgids are capable of reproducing, the population growth tends to be exponential. There is typically a lot of tree death in the first few years after an infestation, but the later waves are usually less destructive due to fewer host trees. It takes several years for new trees to grow large enough to become susceptible host plants. It does appear that once adelgids colonize a stand of trees then they are there permanently.
Management and control of the species
Several insects and spiders may feed on the adelgids, but none have been shown to have a preference for this species in particular. There have been several predator insect species introduced from Europe, but these haven't been shown to have a significant effect so far. If the trees that are attacked can survive for more than 1 to 2 years they may develop a wound layer that is impermeable to insects, but this is not widespread throughout the tree and, as the tree grows, it continues to be susceptible to new attacks.
In the northern latitudes, only adelgids below the snowline will survive the extreme cold, so trees in extreme elevations may be less susceptible than lower elevation individuals.
What about insecticides?
Since the adelgids are hidden in crevices and protected by their wooly coating, arial spraying of large areas is not really effective. Spraying individual trees from the ground has shown to be effective, however. Contact insecticides applied directly to the bark have been shown to be effective against the crawler stage. Insecticidal soaps and oils have been shown to be able to penetrate the waxy coating but it is important to get the timing right so the foliage isn't burned.
The good news is that these adelgids can be managed, but it takes vigilance and consistency to keep their numbers under control. That works fine for Christmas tree lots where individual trees can be monitored and treated, but in the wild, the reality is that this bug has wreaked havoc.
A disturbing example is in the most visited national park in the U.S., Great Smoky Mountains National Park. The Fraser Fir is the only fir species endemic to the Southern Appalachian Mountains and is restricted to high elevations in southwestern Virginia, western North Carolina, and northeast Tennessee.
It has been reported that over 90% of the original population of Fraser Firs in the Smokies has been killed. Below you'll see some stark images to illustrate this point. These pictures were taken in the highest elevations of the Great Smoky Mountains National Park. Pay particular attention to the mountainside in these images where you'll see areas of green interspersed with brown tree remnants. Those dead trees are the Fraser Firs. A quick drive through the highest elevations of the park, up Highway 441 and Clingman's Dome road, will provide excellent views of the devastation on neighboring mountains.
If you want more specifics than I've gone into here, the US Forest Service has an excellent brochure you can download below.
There's also a more specific brochure on Balsam Wooly Adelgid management you can download below. It lists specific chemical agents that are approved to control this species. Until next time.
Madbird Biologist - Mark A. Dunaway
I am a wildlife biologist and nature recording expert who is passionate about our planet and the species we share it with. I am an advocate for conservation and enjoy educating others about the plants and animals around us. Tag along with me as I document what I'm up do or talk about things I think others may be interested in. Thanks for joining me on this journey into the natural world.