Hemlock Woolly Adelgid
(Adelges tsugae)
Biological Category
Terrestrial Invertebrate
NY Legal Status
Prohibited
Species Type
Terrestrial Invertebrate
DESCRIPTION
In winter, Hemlock Woolly Adelgid produce white, cotton-like “woolly” masses at the base of hemlock needles. You can find these woolly masses throughout the year.
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Juvenile Hemlock Woolly Adelgid, known as crawlers, can usually be found at the base of the needles. They insert their long mouthparts and begin feeding on the tree’s stored starches. Hemlock Woolly Adelgid remain in the same spot for the rest of their lives, continually feeding and developing into adults. Their feeding severely damages the canopy of the host tree by disrupting the flow of nutrients to its twigs and needles. Tree health declines, and mortality usually occurs within 4 to 10 years.
All species of hemlock are vulnerable to attack, but severe damage and death typically occurs in eastern (Tsuga canadensis) and Carolina (Tsuga caroliniana) hemlocks only. Eastern hemlock is the most common species of hemlock in New York State.
Spring generation adults lay numerous eggs within large, white, woolly sacs. The eggs hatch and crawlers from the second generation move to attach themselves to new needles. Once they find a site, they settle and become dormant until autumn. At that time, they end their dormancy and begin to feed and develop through the fall and winter. A. tsugae is atypical of most insect species in that it is inactive for much of the growing season and very active throughout the winter.
Adelges tsugae has both sexual and asexual reproduction. The asexual cycle occurs on hemlock while the sexual stage occurs on spruce. A. tsugae has two asexual generations per year on hemlock. Each adult can produce between 50-300 eggs within its lifetime. A. tsugae’s reproductive output, and its lacks of natural enemies has caused populations to explode in North America.
Hemlock woolly adelgids are damaging hemlock ecosystems in eastern North America where both eastern hemlock and Carolina hemlock serve as the hosts. At this time, about 25% of the 1.3 million hectacres have been infested. It has been figured that the entire range of the eastern hemlock is at risk within the next 20 to 30 years.
Immature nympths as well as adults, damage the trees by sucking sap from the twigs. Resulting, the trees lose vigour and prematurely drop their needles, to the point of defoliation, which may lead to death. Once occupying a tree, they can kill the host tree in three to four years if left uncontrolled. Trees of all sizes and ages are attacked, but natural stands aree at the greatest risk. Reduced sales of hemlocks for ornamental use, impacts industries. Hemlocks provide nesting sites and foraging habitat for neotropical migratory birds. There are several threatened and endangered species that requires the hemlock to survive, and face a greater threat with these tree populations being impacted. Large-scale hemlock die-offs will affect species diversity, vegetation structure, stand environmental conditions and ecosystem processes.
Several insects from Asia have been studies, approved, and successfully introduced in HWA-infested areas. These insect predators serve as biological controls as they feed on HWA and reduce their populations. Three insect species from the Pacific Northwest continue to be introduced and their effectiveness as long-term solutions continue to be evaluated.
The beetle Laricobius nigrinus has been released at various locations in the Finger Lakes and Catskills Regions beginning in the 2000s, and has generally been more successful at establishing than Sasajiscymnus tsugae. The silverflies, Leucopis argenticollis and Leucopis piniperda, are a more recent addition to the arsenal. Since 2015 just a handful of releases of these species have occurred in New York. These release sites are still being monitored for establishment and effectiveness.
Specific chemical insecticides can be used to treat an already infested tree or as a preventive measure in a high-risk infestation area. They are useful for treating individual, ornamental, or high-value trees, but are not practical or economical in a forest setting.
Two insecticides that have shown promising results are Imidacloprid and Dinotefuran. Both must be applied by a licensed pesticide applicator, and either can kill Hemlock Woolly Adelgid on its own. Applying both insecticides to an infested tree, however, combines the immediate effectiveness of the fast-acting Dinotefuran with the long-term protection of Imidacloprid, leaving the tree adelgid free for up to seven years.
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