HEMLOCK WOOLLY ADELGID
Stephen Bambara, Extension Entomologist
Robert C. Baldwin, NCDA&CS Plant Industry Specialist
The
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.
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.
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.
Published by North Carolina Cooperative Extension Service
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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
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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
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© 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.