Hemlock Woolly Adelgid (HWA) is a tiny, invasive insect which kills hemlock trees in a matter of 6 years. Please see the previous post on HWA for more information. The insect was introduced in Virginia in the early 1900’s, and has steadily spread since then. New York state contains all stages of HWA infestation. There are heavily infested areas like the lower Hudson Valley, which have harbored HWA for 20+ years and contain increasing numbers of declining and dead hemlocks. Moderately infested areas include the Finger Lakes, where some areas have HWA and some do not. Several HWA early detections were made in Western NY’s Allegany State Park by dedicated volunteers, trained by Park staff to survey for the insect. Allegany just has a few isolated patches of HWA, and State Parks is working to keep those patches small. So far, the Adirondacks have escaped infestation, but they are not immune.
How do we know all this information? The first step in determining if HWA is present is simply to look for it. Surveying for HWA takes diligence; the insects’ most visible life stage is the egg sac, which is present in the fall and winter. A hand lens is necessary to identify the tiny adults in the summer. Primarily through grant funding and volunteers, Parks has surveyed for HWA in 20 State Parks, and that number increases every year.
After surveying, maps are created and examined and hemlock stands are prioritized for treatment. Prioritization is a rigorous process which includes collaboration with state and local experts. These experts ask questions like: Do dead/dying hemlocks pose a health and safety risk here? Is there an area of ecological significance, for example, an old growth stand or is there an insect or animal present which is dependent on hemlocks? Will the loss of hemlocks create a significant, negative change to aesthetics? Is this an area of early detection, where treatments could make a big difference?
Treatment for HWA does exist. Parks has chosen our methods through regular consultation with experts, based not only on what works, but what has the least impact on the environment. Pesticides are carefully sprayed onto the bark of hemlock trees, in the spring or early fall. The pesticides are taken up rapidly through the bark and into the tree, where hemlock’s circulation system takes it throughout the tree, to all the little branches. The HWA will not survive on treated hemlocks for the next 7 years. While this is certainly not a permanent solution, it does buy us much needed time.
In conjunction with these treatments, Parks is also releasing biological control beetles. Biological control insects have an extensive approval process which can take a decade or more through the USDA. Many states have biological control review processes as well, including NY. These processes are designed to assess and evaluate the insect and its host specificity, the reproductive and cross breeding potential, and other factors. If, and only if, the insect is passes the host specificity and other tests, is it approved for release. Many biological control insects have been explored for control of HWA, one showing some promise is Laricobius nigrinus. These biological control beetles feed exclusively on HWA, and while they will not eliminate their food source, they can keep HWA populations in check so they are no longer killing hemlocks. While this is the ideal end result, it can take a decade or more before this is attained. Releasing a few hundred L. nirginus against millions of HWA means we need to buy time, through the use of pesticides, as these beetles work to increase their populations to levels where they can match HWA and keep it in balance.
Invasive insects are notoriously difficult to contain. While we may never stop the onward march of HWA, we can reduce the negative impacts of hemlock loss in specific areas through human intervention.
Post and photos by Alyssa Reid.