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HEMLOCK WOOLLY ADELGID

Stephen Bambara, Extension Entomologist
Robert C. Baldwin, NCDA&CS Plant Industry Specialist

CAUTION: This information was developed for North Carolina and may not apply to other areas.

[General Information] [Biology] [Control] [Other Resources

Adelges tsugae Annand, Phylloxeridae [HOMOPTERA]
(Also called the hemlock chermid, hemlock chermes & hemlock woolly aphid)

General Information

twig with woolly adelgidsThe hemlock woolly adelgid is a small (1/32 inch), reddish-purple, aphid-like insect that covers itself with a white, fluffy secretion with a complicated life history. and may use spruce as a secondary host.

Some adults have two pairs of wings. Their mouthparts are thread-like and about 1/16 inch long and used to suck sap. Sucking sap from young twigs retards or prevents tree growth and causes needles to turn grayish-green, and drop prematurely. The loss of new shoots and needles is highly detrimental to a tree's health. A tree may defoliate and die within several years.

Eggs are brownish-orange, but darken as the embryo matures. The eggs are also hidden within the white, fluffy secretion. When the eggs hatch, flat, naked, reddish-brown adelgid crawlers move about actively. Once the crawlers settle, they become black with a white fringe around the edge and down the center of the back. Young adelgids live on twigs or at the bases of old needles. They soon secrete a white, fluffy "wool" that completely covers their body. The wingless nymphs resemble adults but are smaller. Infested branches become covered with circular, fluffy, white blobs. Adelgids are parthenogenic and only females are known.

Biology

The hemlock woolly adelgid only survives on hemlock (Tsuga sp.). This is an extremely damaging pest of hemlock, especially Tsuga canadensis and Tsuga caroliniana, out two native hemlock species on the east coast. This insect is thought to have been transported to North America from the Orient. It has been known in the Pacific Northwest since 1927. In recent years, hemlock woolly adelgid was found in the Northeastern US where it has become a severe pest. It was first reported in North Carolina in 1995. In 2005 (Click here for distribution map), surveys show that hemlock woolly adelgid is known to be in most of the counties where Tsuga sp. is endemic. Infested hemlocks become covered with dirty white globs of cottony puffs. Infested trees defoliate prematurely and may die eventually. Natural stands of hemlock are at greatest risk for death. Landscape plantings may need treatment if infested.

The hemlock woolly adelgid overwinters as a female within the fluffy mass. Egg laying begins in February. Tiny crawlers hatch from the eggs and settle down to feed. Older nymphs secrete the fluffy, white "wool". Some nymphs develop into a winged form that leaves hemlock to lay eggs on an alternate host such as spruce. The remaining nymphs develop into wingless females that lay eggs in a fluffy mass on hemlock. Wind and animals disperse this insect. The second generation of adelgids on hemlock settle down as young nymphs in July to spend most of the summer as tiny black insects with a white fringe. In October or November, they molt, grow, and produce the fluffy white mass.

Control

The hemlock woolly adelgid is a difficult insect to control because the fluffy white secretion protects its eggs from pesticides. A good time to attempt control it is in October when the second generation begins to develop. The insecticidal soap and the horticultural oil sprays seem to be very effective for adelgid control with minimal harm to natural predators and parasites of this pest. Trees that are heavily infested and are showing symptoms of decline should probably be sprayed. Horticultural spray oil can be applied during the winter and before new growth emerges in spring. Oil sprays may damage hemlock during the growing season, especially in dry weather. Registered pesticides containing imidacloprid or dinotefuran may be useful for specimen trees located away from water sources. These insecticides are systemic and are often applied as soil injection.  Dinotefuran may be applied as a trunk spray.  Dinotefuran has a faster uptake, and imidacloprid has a longer residual protection. For additional pesticides, consult the North Carolina Agricultural Chemicals Manual, "Trees and Woody Ornamentals" Section, Adelgids.  Researchers with NCSU, in cooperation with the NC Dept. Agriculture and Consumer Services, are conducting biological control strategies using releases of a tiny Japanese lady beetle, Sasajiscymnus tsugae (formerly Pseudosymnus tsugae) in hopes of reducing the damage this pest causes to hemlocks. Scymnus sinuanodulus and Scymnus ningshanensis are two additional lady beetles recently introduced.   Laricobius nigrinus, a native beetle from western  North America is being tested. Similar programs in other states have shown good results.

For more complete management information see:
Hemlock Woolly Adelgid - US Forest Service
USDA Forest Service Photo Gallery
NC Cooperative Extension Note: Hemolock Woolly Adelgid Control in the Landscape  or as an
MSWord download http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note119a/note119hwa.doc

Economic Impact of the Hemlock Woolly Adelgid on Residential Property Values. Ph.D. Dissertation by Elizabeth Anne Murphy, 2004.



Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance contact an agent of the North Carolina Cooperative Extension Service in your county.
© 2001 NC Cooperative Extension Service

Prepared by:
Stephen Bambara, Extension Entomologist
Robert C. Baldwin, NCDA&CS Plant Industry Specialist

ENT/ort-119 April 2000 , lightly revised 2009
Web page last reviewed January, 2011 by the webperson.