Tag Archives: biocontrol

Wasp Warriors Aid Parks Against Insect Invaders

If you haven’t noticed, New York’s ash trees have been struggling lately. Over the last few years, they have been rapidly dying due to a little iridescently green insect: the emerald ash borer (EAB).

An invasive beetle native to parts of Asia and Russia, EAB was first discovered in New York in Cattaraugus County in 2009. It has since spread to 55 of New York’s 62 counties, decimating once thriving ash populations.

Since its discovery in southeast Michigan in 2002, EAB has spread into 35 states and the District of Columbia, killing tens of millions of ash trees in their wake.

EAB is widespread in the eastern U.S. as show in this USDA map. Each red dot represents an infested county and the blue line is a federal quarantine zone.

Emerald ash borers lay eggs between bark layers and in bark crevices on ash trees. Upon hatching, the larvae burrow through the bark and begin to feed on the tree’s living parts: the phloem and sapwood. The larval feeding creates galleries, which cut off the movement of nutrients throughout the tree. Eventually, as the infestation grows, the tree’s system of nutrient transport ceases to function, and the tree slowly starves and dies.

EAB larvae create S-shaped “galleries” where they feed just beneath the bark of an infested ash tree. Use the slider bar to explore the damage in this tree.

Ash trees are important for so many reasons. They provide cool shade in the summer heat, provide habitat for wildlife, and are a valuable source of timber and firewood. When large ash die, however, they can pose serious safety risks. Dead and dying trees often bring down powerlines along the road and cause blackouts.

In addition, many trails, campgrounds, parking lots and playgrounds are surrounded by ash that, once infested, become hazard trees that require removal. Parks’ staff must constantly monitor public use areas for the presence of dying trees that may pose a risk to patrons.

The fight to conserve ash has been an uphill battle. While pesticide treatments work, they only last a year or two before reapplication is necessary and also are too expensive to use everywhere. Statewide quarantines and public education have helped slow the spread, but these little beetles can fly over a mile and lay up to 200 eggs in a lifetime, making containment difficult.

This chart shows the lifecycle of the EAB. (Photo credit – Cornell University)
State Parks staff at Jacques Cartier State Park peel back bark from an infested ash tree to reveal the EAB damage. (Photo credit- Aaron Hemminway, NYS Parks biologist)

You may be thinking “what can be done?!” Well with National Invasive Species Awareness Week coming May 17-23, an update from State Parks is timely.

Luckily, we may finally have a cost-effective, sustainable, and chemical-free solution to the problem. For the second year in a row, the state Office of Parks, Recreation and Historic Preservation and the U.S. Department of Agriculture (USDA) are partnering to release three species of predatory wasps – known ecologically as biological controls or parasitoids – to battle EAB in select state parks.

These tiny warriors are heavily studied little predators from the EAB’s home countries which prey only on these beetles and pose no risk to our native ecosystem. (And don’t worry. These wasps don’t sting and are no threat to people).

The females of these species attack ash borers in the early stages of their life cycle. These three wasps were chosen because they each have slightly different ways of tackling EAB, making them a more effective as a group.

Here, let’s meet our winged team.

Tetrastichus planipennisi

Tetrastichus planipennisi females lay eggs inside of EAB larvae, where the parasitoid larvae grow and eventually kill their host. They are used to protect smaller ash trees in particular, and they originate in China.


Oobius agrili

Oobius agrili lay eggs inside EAB eggs, where the parasitic wasp larvae hatch, grow, and kill the host EAB egg. These wasps are all female, so they reproduce asexually. They also originate in China.


Spathius galinae

Spathius galinae lay eggs outside of EAB larvae; when they hatch, Spathius feed on the EAB larvae, killing it. These wasps are best at helping larger ash trees, and are collected in the Russian Far East.


Last year, 11 State Parks received about 40,000 Tetrastichus wasps: Rockland Lake in Rockland County; Harriman and Bear Mountain in Rockland and Orange counties; Minekill in Schoharie County; Beaver Island and Buckhorn Island in Erie County; Clay Pit Ponds in Staten Island; Lakeside Beach in Orleans County; Golden Hill in Niagara County; Southwick Beach in Jefferson County; and Point Au Roche in Clinton County.

Starting this month, Jacques Cartier State Park in St. Lawrence County and Ganondagan State Historic Site in Ontario County will be added to that list. All three wasp species will be deployed, with an expected total of more than 50,000 wasps. All the wasps used are reared in a lab in Michigan, where they are shipped to New York and other states where USDA is coordinating its EAB biocontrol program.

For the wasps to be successful here, they need to find the beetle in its early life stages. In New York, the emerald ash borer generally begins to lay eggs in the summer; however, many larvae overwinter inside of ash trees, and are thus readily available as food for the parasitoids in the spring.

Parks staff introduces the wasps into infested ash trees through three methods:


  • Ash bolts are small sections of ash (think small ash logs slightly larger than cans of soup) that house mature parasitoid larvae. They are attached to infested ash trees using twine or zip ties. When the larvae mature, they leave the bolts and find EAB larvae to feed on within the ash stand.
Ash bolts are attached to infested trees with zip ties or twine, and are marked with flagging so they can be easily found. Please don’t disturb or tamper with the bolts if you come across them!

  • Plastic cups containing adult parasitoids arrive on-site ready for distribution. The cups simply need to be opened, inverted and tapped gently against the trunks of infested trees.
Adult parasitoids arrive in plastic cups, ready for release.
  • Oobinators are used less frequently and only for the delivery of Oobius agrili. They are small, plastic pill bottles with a screen over the open end that can be attached to trees with zip ties or twine. They contain a sheet of paper with parasitized EAB eggs. Once mature, Oobius will hatch and escape through the screen.
Oobinators are hung upside down, to allow mature parasitoids to escape. Photo credit: USDA

While out exploring NYS Parks, you may see these “ash bolts” or “Oobinators” attached to trees. They are often marked with flagging for easy identification. While it may be tempting to try to get a closer look at these woodland wasp homes, it is important to let the parasitoids grow and feed uninterrupted,  to give them the best possible chance of survival.

While parasitoid releases may be new to New York State Parks, USDA has been conducting releases throughout the country for several years. Subsequent studies indicate that that wasps are surviving and are feeding on the EAB.

Studies have also shown that the Tetrastichus wasps in particular can eliminate up to 85 percent of EAB larvae in ash saplings. (Duane et al., 2017)

These are promising results which suggest if parasitoid wasps can be reared in abundance, they may offer crucial protection to the next generation of ash trees. It is important to keep in mind, however, that success will not happen overnight. Wasps need to find enough EAB to build up their populations to sustainable levels and it takes time to see results, even if wasp populations are doing well. Parasitoids also will most likely not save most larger ash, but they can help manage EAB populations so smaller ash trees can have a chance grow and hopefully reproduce.

Parks is thrilled to partner with USDA in this important endeavor to protect our forests. You also can join in the effort by reporting emerald ash borer sightings or suspected damage to the iMapInvasives website or smartphone app. There is also a USDA online reporting form here.

Also, help stem the spread of EAB and other invasive forest pests by following state regulations that control the movement of untreated firewood, which can carry these invasive hitchhikers.

  • Untreated firewood may not be imported into NY from any other state or country.
  • Untreated firewood grown in NY may not be transported more than 50 miles (linear distance) from its source or origin unless it has been heat-treated to 71° C (160° F) for 75 minutes.
  • When transporting firewood, the following documentation is required:
    • If transporting untreated firewood cut for personal use (i.e. not for sale) you must fill out a Self-Issued Certificate of Origin (PDF).
    • If purchasing and transporting untreated firewood, it must have a receipt or label that identifies the firewood source. NOTE! Source is sometimes, but not always, the same as where it was purchased. Consumers need to use the source to determine how far the firewood may be transported.
    • If purchasing and transporting heat-treated firewood, it must have a receipt or label that says, “New York Approved Heat-Treated Firewood/Pest Free”. This is the producers’ declaration that the firewood meets New York’s heat-treatment requirements. Most “kiln-drying” processes meet the standard, but not all, so it is important to look for the appropriate label. Heat-treated firewood may be moved unrestricted.

Find out if your destination is within the 50-mile movement limit by using this interactive map from the state Department of Environmental Conservation.

Finally, if you encounter evidence of biocontrol release sites while out on State Parks trails, know that you are in the presence of these wasp warriors, engaged in a battle to save our beloved ash trees.

Above, Parks staff hang ash bolts and record release data used by USDA to measure the effectiveness of the project to combat the Emerald Ash Borer.


Cover shot – Emerald Ash Borer (Original Artwork – Juliet Linzmeier, Student Conservation Association member with NYS Parks) All other photo credited to NYS Parks unless otherwise noted.

Post by Sarah Travalio, Terrestrial Invasive Species and Biocontrol Coordinator, New York State Parks


Here are other easy tips that can make a big difference in helping stop the spread of all invasives:

  1. Clean, drain, and dry your watercraft and gear thoroughly to stop the spread of aquatic organisms.
  2. Plant only non-invasive plants in your garden, or even better, plant native plants. You can use the New York Flora Atlas to check which plants are native to New York.
  3. Clean your boots or your bike tires at the trailhead after hitting the trail – seeds of invasive plants can get stuck on your boots, clothes, or tires. You don’t want invasives in your yard or your other favorite hiking spots.
  4. Get involved – volunteer to help protect your local natural areas, join your local PRISM (Partnership for Regional Invasive Species Management) to stay informed, or become a citizen scientist by using iMapInvasives to report infestations of invasive species right from your smartphone.

Interested in taking a deep dive into research on the parasitoid battle against the EAB? Check out these scientific studies:

Jian J. Duan, Leah S. Bauer, Roy G. Van Driesche, Emerald ash borer biocontrol in ash saplings: The potential for early stage recovery of North American ash trees, Forest Ecology and Management, Volume 394, 2017, Pages 64-72, ISSN 0378-1127, https://doi.org/10.1016/j.foreco.2017.03.024.

Duan, Jian J., Leah S. Bauer, Kristopher J. Abell, Michael D. Ulyshen, and Roy G. Van Driesche. “Population dynamics of an invasive forest insect and associated natural enemies in the aftermath of invasion: implications for biological control.” Journal of Applied Ecology 52, no. 5 (2015): 1246-1254. https://doi.org/10.1111/1365-2664.12485

Jian J Duan, Roy G Van Driesche, Ryan S Crandall, Jonathan M Schmude, Claire E Rutledge, Benjamin H Slager, Juli R Gould, Joseph S Elkinton, Establishment and Early Impact of Spathius galinae (Hymenoptera: Braconidae) on Emerald Ash Borer (Coleoptera: Buprestidae) in the Northeastern United States, Journal of Economic Entomology, Volume 112, Issue 5, October 2019, Pages 2121–2130, https://doi.org/10.1093/jee/toz159


Big Hopes for Little “Army” in Parks’ Fight against Hemlock Invaders

As the third most common tree in New York, hemlocks fill our forests and are found in many New York State Parks. Located along hiking trails, streams, gorges, campsites, and lake shores, the evergreens can live to be hundreds of years old, providing vital ecosystem services and supporting unique habitats.

In addition to providing homes and food for many forest creatures, hemlocks also keep fresh water resources cool and clean by moderating water temperature and acting as a natural filtration system along streams. Since hemlocks are such a critical component of eastern forests, they are known as a “foundation species.”

Hemlocks in New York have been under attack by an invasive forest insect pest that originated from southern Japan, the hemlock woolly adelgid (HWA), which after being found in Virginia in the 1950s has spread to kill untold millions of hemlocks from Georgia to Maine.

Hemlock Woolly Adelgid infestation in the Eastern U.S. (U.S. Forest Service)

Adelgids are tiny insects that insert piercing-sucking mouthparts into hemlock twigs, causing damage to woody tissue that inhibits water and nutrients from reaching emerging hemlock buds. This limits the growth of new twigs and eventually kills the tree.

First detected in New York in the 1980s, the insects have spread through the Hudson Valley, Catskills, Southern Tier and Finger Lakes regions. Infested hemlocks can be found at state parks including Harriman, Minnewaska, Taughannock Falls, Watkins Glen, Letchworth, and Allegany.

At about 6/100ths of an inch long, the flightless adelgids are hard to spot, but in the winter through early summer leave distinctive white “woolly” egg masses on hemlock twigs. In an infestation, developing buds are killed first, then in a few years, the weakened tree loses its needles and dies.

Left, a dead hemlock after being killed by HWA. Right, a healthy tree.
A map of New York State towns and counties where HWA had been found in the Hudson Valley, Capital Region, and Southern Tier by 2017. The HWA has yet to move into the Adirondacks or the Tug Hill Plateau. (State Department of Environmental Conservation)

The threat posed by HWA is dire, especially since the state’s ecosystems lack natural controls _ known as biocontrols _ such as predators or tree resistance that could fend off some infestations and avert widespread hemlock destruction.

Currently, insecticide treatments are our only sure option for saving trees, but trees must be treated on an individual basis, so it can be costly or impractical to treat large swaths of hemlocks. In parks with thousands of trees and important or rare ecosystems to protect, biocontrol is the only solution to counter a pest like HWA.

But biocontrol against the invading adelgid may be on the way. It is the form of a small dark beetle and a small silvery fly, nicknamed “Little Lari” (Laricobius nigrinus) and “Little Leuc” (Leucopis spp.), respectively, by researchers at the New York State Hemlock Initiative at Cornell University.

Led by forest entomologist Mark Whitmore, the program operates a biocontrol lab researching the introduction of HWA predators throughout New York, hoping to protect hemlock trees by slowing the spread of adelgids into new areas.

The NYSHI collects these predators in the Pacific Northwest where HWA is native and has many predators controlling population growth so the hemlocks are not damaged. The collected beetles and flies are shipped to the quarantine facility at Cornell  to be certain none of the western adelgids are accidentally introduced into New York with the predators.

Knowing where to release these “good bugs” can be a challenge, but we are helped in this by State Parks staff, who provide critical data from ground surveys to find emerging infestations, assess potential biocontrol sites, and monitor for whether the biocontrol insects are thriving and growing in their new homes.


Read this post in the State Parks blog by Abigail Pierson, state Parks Forest Health Specialist, to learn how crews search for and document the presence of HWA.


Since 2009, the Cornell initiative has released more than 4,500 Laricobius beetles in State Parks including Harriman in Rockland County, Letchworth in Wyoming County, Mine Kill in Schoharie County, and Taughannock Falls, Buttermilk Falls, and Robert H. Treman in Tompkins County. Additionally, parks staff at Minnewaska State Park Preserve in Ulster County helped survey for Laricobius beetle establishment, and mapped hemlocks to help identify hemlocks stands and prioritize HWA surveys in the park. 

Since 2015, when Leucopis silver fly releases began, researchers have released more than 3,300 flies at several state park sites including Taughannock Falls and Buttermilk Falls state parks in Tompkins County.

“Little Lari” (Laricobius nigrinus) (New York State Hemlock Initiative)
“Little Leuc” (Leucopis spp.) (New York State Hemlock Initiative)

While there has been no evidence of the biocontrol bugs suppressing HWA populations on a large scale, it takes time for predator populations to build. There has been recovery of Laricobius beetles at some sites, indicating establishment. By continuing to release more “Little Laris” and “Little Leucs” to bolster those established populations, we will be able to build on that initial success.

The list of parks that have reported HWA infestations is growing, especially in the Capital Region. Thacher State Park in the Capital Region reported adelgid infestations in 2017 and while insecticide treatments reduced the local problem, the insects continue to threaten the Adirondacks, which so far remains uninfested.

In State Parks, preventing dead trees from injuring park visitors or damaging park infrastructure including campsites and trails is crucial. Additionally, preventing the loss of a critical foundation tree species in forest habitats is another major priority.

Park visitors can play an active role in slowing the spread of the adelgid in New York by keeping an eye on hemlocks. Reporting any infestations that you find provides researchers and land managers with invaluable data for improving our management efforts.



How You Can Help

If you believe you have found HWA:

  • Take pictures of the infestation signs (include something for scale such as a coin or ruler).
  • Note the location (intersecting roads, landmarks or GPS coordinates).
  • Fill out the hemlock woolly adelgid survey form.
  • Email report and photos to Department of Environmental Conservation Forest Health foresthealth@dec.ny.gov or call the Forest Health Information Line at 1-866-640-0652.
  • Contact your local Partnership for Regional Invasive Species Management (PRISM) by visiting http://www.nyis.info/.
  • Report the infestation at iMapInvasives.
  • Slow the spread of HWA in our forests by cleaning equipment or gear after it has been near an infestation, and by leaving infested material where it was found.

The New York State Hemlock Initiative has produced a variety of educational videos on the threat posed to hemlocks by the HWA.


Cover Photo: A hemlock branch showing the woolly white egg masses of Hemlock Woolly Adelgid. (New York State Department of Environmental Conservation)


Post by Charlotte Malmborg, Education and Outreach Technician, New York State Hemlock Initiative, Cornell University Dept. of Natural Resources

Lose the Loosestrife: Beetles for Biocontrol

Purple loosestrife (Lythrum salicaria) is an invasive plant from Europe and Asia that can overcrowd native wetland plants. It is easily recognized by its tall and showy purple spike of flowers in the summer, lance-shaped leaves and square stems. As an invasive species, it lacks its natural predators and can spread quickly, producing as many as 2.7 million seeds a year.

Loosestrife flower, photo by A McGinnis
Purple loosestrife flower spikes at Silver Lake State Park. Photo by Amy McGinnis

Wetlands are rich habitats that support a diversity of plant, insect and animal species, such as marsh marigold (Caltha palustris,) twelve-spotted skimmer dragonfly (Libellula pulchella,) painted turtle (Chrysemys picta,) green heron (Butorides virescens.)  The introduction and spread of purple loosestrife has resulted in the loss of native plant and animals that depend on wetland habitats. In addition, purple loosestrife limits the growth of rare plants and can clog drainage ways and ditches, negatively affecting adjacent land and crops.

Loosestrife in bloom, photo by Amy McGinnis
Purple loosestrife plants in bloom at Silver Lake State Park. Photo by Amy McGinnis, State Parks

Since purple loosestrife grows in wetlands, methods to control this plant and promote native biodiversity aren’t always easy. Small young infestations can be removed using hand tools, but care must be taken to dig out all of the root portions to avoid regrowth. This may not be feasible for larger, more established infestations. The flower heads cut be cut, bagged and disposed of to prevent seed production and the spread of this plant. Chemical herbicides can be utilized by licensed applicators that follow strict protocols to avoid contaminating water bodies and non-target native species. However, there is an easier way to fight this invasive: biological control or biocontrol. Biocontrol is the control of an invasive species by introducing a natural predator of that species following very specific federal and state regulations and testing to make sure there will be no other negative impacts on the ecosystem. In this case, the biocontrol is the small purple loosestrife beetle, a beetle of the genus Galerucella. These are native to Europe and Asia and feed on purple loosestrife in its native range, keeping the plant in check.

Scientists must thoroughly test any biocontrol species to make sure they only affect the target invasive species and don’t negatively impact native species. In the U.S., studies have shown the beetles to be very host-specific, feeding and reproducing predominately on purple loosestrife. The beetles do not completely eradicate purple loosestrife, but they suppress the plants’ growth and ability to reproduce by feeding on its stems, buds and leaves. Thus, they reduce the plants’ dominance and impact within the ecosystem.  Since 1992, biologists working under state and federal permits have released millions of these beetles at numerous sites across the northeast, including at several New York State Parks, such as Silver Lake State Park in western NY.  In NY, the Department of Environmental Conservation continues to monitor the numbers and effectiveness of the beetles and to ensure there are no unforeseen problems.

The beetles are released in the summer when loosestrife is actively growing. They overwinter in the soil near the host plants and emerge in the spring to reproduce, with females laying eggs from May to June. When they hatch, the larvae feed on the loosestrife’s young growth and work their way down the plant where they eventually enter the soil to pupate. They emerge as adults in the summer and the cycle continues. Though they are not strong fliers, occasionally the beetles have been found 10-12 miles away from the initial release site.

Release sites for the beetles are determined by the dominance of purple loosestrife. These sites usually have a high percentage of loosestrife plants where hand removal of them is difficult. Biologists must submit an application to the Department of Environmental Conservation to justify the need for the beetles and receive a permit. The number of beetles depends on the size of the purple loosestrife infestation. Silver Lake State Park is one location where the beetles have been used as a biocontrol for this invasive plant. Silver Lake has an approximate 40 acre wetland with a purple loosestrife population of about 15%. In 2010, 800 Galerucella beetles were released in an effort to control the loosestrife. One meter by one meter plots were established in order to monitor the survivorship of the beetles and the defoliation, or the loss of leaves, stems and flowers, of the plants where the beetles have fed on them. Each summer after the beetles have emerged, the plots are assessed to determine the effectiveness of the beetles and if any more should be released. This is done by looking at the number of loosestrife plants that are defoliated (eaten, not flowering) vs. the number that are flowering, as well as the number of beetles that are seen. More beetles have been released at Silver Lake State Park since the initial 800 in 2010; the purple loosestrife plants have remained contained to that area and their growth has been restricted.  In 2016, State Parks biologists expanded the program to Letchworth State Park.

The extent of purple loosestrife has declined dramatically in areas with this biocontrol. It is unlikely that the beetles will eliminate purple loosestrife populations entirely. The hope is that as more Galerucella beetles are released across the state, the invasive loosestrife will be diminished, making room once again for the native flora and fauna at these sites.

Beetle on loosestrife at Silver Lake SP, photo by A McGinnis
Galerucella calmariensis beetle on a purple loosestrife leaf at Silver Lake State Park, photo by Amy McGinnis, State Parks

Post by Amy McGinnis, State Parks

Featured image, Galerucella calmariensis beetle on a purple loosestrife, by Amy McGinnis, State Parks

Invasive Species Spotlight: Monitoring for Hemlock Woolly Adelgid

Hemlock Woolly Adelgid appears as white fluffy balls on the underside of hemlock branches during the cooler months.
Hemlock Woolly Adelgid appears as white fluffy balls on the underside of hemlock branches during the cooler months.

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.

map
This map shows the spread of HWA by township since 1987. Map from http://www.dec.ny.gov/animals/7250.html.

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.

Survey technique demonstration for volunteers in Allegany State Park.
Survey technique demonstration for volunteers in Allegany State Park.

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?

Mark Whitmore, of Cornell University, gazing at a hemlock in serious decline at Minnewaska State Park Preserve.
Mark Whitmore, of Cornell University, gazing at a hemlock in serious decline at Minnewaska State Park Preserve.

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.

Sign up for an upcoming iMap Invasives training to learn how to report HWA when you spot it in State Parks’ forests.

Post and photos by Alyssa Reid.