https://en.wikipedia.org/wiki/Hemlock_woolly_adelgid#/media/File:Adelges_tsugae_3225077.jpg

Hemlock Woolly Adelgid

Adelges tsugae

Introduction

Unfortunately Hemlock Woolly Adelgid (HWA) has been spotted on our preserves since early 2022. We are actively monitoring our preserves for HWA and you can help us! If you spot evidence of HWA on one of our preserve, please report it to Isaac at ischuchat@kporttrust.org. In the email, please include a picture of the HWA, a description of the location and the GPS coordinates (can be found by clicking on “my location” in your phone app).

HWA is an insect species originating from Japan that attacks eastern hemlock trees. HWA is native to Japan, India, Nepal, southwestern China, and Taiwan. Though original transmission of HWA to the United States is unknown, from nursery stock imported from Asia. HWA was first found in the United States in 1950s Virginia. By the 1980s, HWA caused widespread mortality of eastern hemlocks and has since spread to 16 states on the eastern seaboard, from Georgia to Maine. Since 1993, the HWA infestation has spread at a rate of approximately 17 kilometers per year. In Maine, HWA are most commonly found in coastal regions. The lifecycle of HWA leads to an unfortunate rapid increase in population. Egg production in early spring and again in early summer has a multiplier effect on the Hemlock Woolly Adelgid population, which if unchecked by predators or other variables, results in an exponential increase in population growth.

https://entomology.ca.uky.edu/ef452

Recognizing Signs of the Hemlock Woolly Adelgid

The Hemlock Woolly Adelgid can be spotted by the presence of a white wooly substance on the twigs of hemlock trees. While these wooly masses on hemlock twigs are known for being present year round, they are most abundant and noticeable in the spring when eggs of the HWA are present. This wooly substance is a waxy material that comes out of the pores of the insect’s body as it feeds.

Hemlock trees are injured by the presence of the Hemlock Woolly Adelgid because the insects inject poisonous saliva into the hemlock tree while feeding (sucking sap from the hemlock trees). The toxic saliva causes the needles of the tree to dry, turn grayish-green in coloring, and they eventually fall from the tree. Buds and potential buds of the hemlock tree are also killed by HWA infestation. Trees infested by the HWA are oftentimes more prone to diseases and other wood-boring insects, and are more likely to be broken or thrown by wind.

HWA populations spread due to the wind, birds, and by deer and other mammals (including humans). Transporting HWA infested trees spreads the Hemlock Woolly Adelgid population.

Establishment of the Hemlock Woolly Adelgid in Maine

As of 2020, the Hemlock Woolly Adelgid is known to be established in the following Maine townships:

  • Cumberland County: Brunswick, Cape Elizabeth, Cumberland, Falmouth, Freeport, Frye Island, Great Diamond

  • Island, Harpswell, Raymond, Scarborough, South Portland, Standish, Yarmouth.

  • Knox County: Camden, Friendship, Owls Head.

  • Lincoln County: Boothbay, Boothbay Harbor, Bristol, Edgecomb, South Bristol, Westport Island, Wiscasset. Sagadahoc County: Arrowsic, Bath, Georgetown, Phillipsburg, Topsham, West Bath, Woolwich.

  • York County: Alfred, Arundel, Berwick, Biddeford, Eliot, Kennebunk, Kennebunkport, Kittery, Lebanon, Ogunquit, Old Orchard Beach, Saco, Sanford, South Berwick, Wells, York.

Slow-the-Spread Program for Hemlock Woolly Adelgid

Management tools: Quarantine, Surveys and monitoring, chemical control, biological control, and outreach

Quarantine:

External (between states) and internal (within Maine) quarantines regulate the movement of hemlock materials to reduce the unintentional movement of HWA.

surveys and monitoring:

Maine Forest Service personnel regularly survey to locate new infestations and monitor the spread of HWA. Impact assessment plots have been established at five sites in Maine. Data from these sites will add to the understanding of forest impacts of the HWA, and will be analyzed alongside information collected from Vermont, New Hampshire, Massachusetts, and Connecticut. (Impact plot summary).

Chemical Control:

The most effective way of removing HWA is utilizing insecticides. In New York, the two utilized insecticides are imidacloprid and dinotefuran. The insecticides are applied on the bark at the base of the tree and are absorbed and spread throughout the tissue of the tree. When HWA feeds from the tree, they are fatally poisoned.

Insecticides are applied to hemlock trees during the spring and autumn when soils are the most moist (when hemlock trees are actively growing and water uptake by the trees is at its greatest). The most optimum time for insecticide application is in the spring when the soil thaws after frigid winter temperatures.

Unfortunately, the insecticides used to treat HWA are neonicotinoids, which have been correlated with harming pollinator populations (like bees). Since these insecticides are indiscriminately harmful to all insect and have the potential to leach into soil and water, we hesitate to use them to control HWA.

Additionally, insecticide application can unintentionally lead to an increase in secondary pests, such as spider mites and scales. Biological control methods (with predators and pathogens) is the preferred approach to managing HWA populations in Maine.

Biological Control:

Biological control methods utilize naturally occurring threats to the HWA species (predators, parasitoids, or pathogens). There are no known parasitoids to the HWA population and there are only a few predators to HWA in the United States. Some non-host-specific, native fungi have been found to infect HWA, but this hasn’t been observed yet. Unfortunately, native predators to the HWA in the United States are not effective enough to control HWA.

Two beetle species that exclusively feed on adelgids have been released in Maine. The beetle species are the Sasajisymnus Lady Beetle from Japan and the Scymnus Lady Beetles from China. Release sites of the beetles are monitored periodically for beetle establishment (monitoring protocol). Impact assessment plots have been established at two release sites. Maine Forest Service cooperates in ongoing research into fungal agents of disease. Biological control is the best hope for long-term control of Hemlock Woolly Adelgids in Maine.

  • Sasajicymnus tsugae - Explorations for natural predators to the Hemlock Woolly Adelgid have begun in Japan in 1992. The Sasajicymnus tsugae, or tiny lady beetle, proved to have great potential in managing the HWA population. Adult tiny lady beetles are black, about 2mm long, and fortunately, both larvae and adult beetle populations feed on all stages of the Hemlock Woolly Adelgid. In 1995, the tiny lady beetle was released into the United States. Studies at the Connecticut Agricultural Experiment Station showed it to have high potential reproductive output over its lifetime and have long lifespans. Field site releases of S. tsugae began in Connecticut in 1995 and elsewhere in 1999. Since 1995, over one million S. tsugae have been released on more than 100 sites in 15 eastern states from South Carolina to Maine.

    • At 4 forested sites in Connecticut and Virginia, initial field releases of S. tsugae on hemlock branches have shown good potential for reduction in HWA populations. HWA densities were 47-83% lower in the area of S. tsugae release. Some sites previously infected by HWA with dieback have demonstrated the ability to recover and produce new shoots due to the introduction of S. tsugae release.

  • Scymnus Lady Beetles from China - research of predators to HWA from 1995-1997 in China had been undertaken. More than 54 species of lady beetle were collected during this time of research and it was found that the Scymnus species was the most abundant species feeding on HWA.

    • Sleeve cages are being used to evaluate the impact of beetle populations on Hemlock Woolly Adelgids. Adelgid Woolly masses on hemlock branches are counted in April. After counting, either a lone female beetle or male/female beetle pair is placed in a mesh bag. This mesh bag is then placed on the hemlock branch tip infested with about 300 adult Hemlock Woolly Adelgids, which is a number far more than the beetle species are expected to eat. Mesh bags with absolutely no beetles are used as the experiment’s controls. In late June, the bagged branches are brought to the lab and the number of HWA and beetles are counted to compare to the original number. In this study, the HWA populations were lower in the mesh bags containing Scymnus beetles than in the control bags (the bags with no beetles and only HWA). By preventing low HWA populations from increasing, the Scymnus beetle stabilizes the population. This prevents the return of HWA on hemlock trees.

  • Laricobius nigrinus : Dr. Lee Humble, a scientist with the Canadian Forest Service in British Columbia, observed that the beetle Laricobius nigrinus consistently feeds on Hemlock Woolly Adelgids in western hemlock seed orchards. Drs. Scott Salom and Loke Kok visited these orchards between 1997 and 2003, imported these beetles to Virginia to study under quarantined conditions. They determined that L. nigrinus will feed on other adelgids, but prefer to feed on HWA. L. nigrinus was removed from quarantine in 2000. The following year, Virginia Tech began field evaluations of and explored ways to rear the insect on a large scale. Rearing HWA predators is very labor intensive, due to the amount of food required to maintain and build L. nigrinus colonies. There are also additional complications in rearing. L. nigrinus requires cold temperatures and the species must live in soil. Field evaluations of L. nigrinus have been promising. The species killed more than 50% of HWA in sleeve cages.

  • Pathogens

    Insect-killing fungi - Thousands of Hemlock Woolly Adelgids, many showing signs of fungal infection, were collected from hemlock forests along the eastern seaboard of the U.S. and from southern China. From the collected HWA, 79 different insect-killing fungal isolates were recovered. Lab studies were conducted to verify that these isolates actually infect HWA. Field tests had been performed to determine “optimal formulations” and spray delivery systems, rates, and timings. Although research is on-going, fungi seems to have great potential for managing Hemlock Woolly Adelgid populations.

Predators are the most effective tool in managing invasive Hemlock Woolly Adelgid populations. Such researched species have yet to show signs of negative impacts on hemlock hosts. Fungi may be the most effective in controlling the HWA infestation on hemlock. In effect, fungi and predators to HWA could work in combination with each other to maintain HWA populations while continuing to leave no negative or unintended impacts on hemlock populations. The researched predators to HWA are to be used as long-term control methods rather than immediate control methods.

What can you do to reduce the spread of the Hemlock Woolly Adelgid?

Do not remove hemlock trees, seedlings, or nursery stock from infested areas!

  • Check hemlock trees and plantings for Adelgids. 

  • Monitor hemlock trees regularly for signs of HWA

    • Inspect new growth for cotton ball-like woolly masses on hemlock twigs (found usually at the base of the tree’s needles).

    • Look twice a year (in late March, when eggs are present and the woolly substance is fluffiest, and in early November, look on new growth where HWA nymphs have started to feed and develop their waxy coating.

    • Use photo guides!

    • Cover areas that you are concerned about

    • Do not fertilize hemlock trees near infested areas

    • Remove bird feeders in the spring and summer

    • IF YOU HAVE FOUND A HEMLOCK WOOLLY ADELGID, REPORT IT HERE

Sources

https://www.dec.ny.gov/docs/lands_forests_pdf/hwamgmtfaq.pdf

https://wiki.bugwood.org/Archive:HWA/Introduction

https://www.maine.gov/dacf/mfs/forest_health/insects/hemlock_woolly_adelgid_fact_sheet.htm