Adelges tsugae
(hemlock woolly adelgid)

Pictures

Picture	Title	Caption	Copyright
Title Adults on Hemlock sprig Caption Adelges tsugae (Hemlock woolly adelgid); adults on Hemlock sprig. USA. Copyright ©Tom Coleman/USDA Forest Service/Bugwood.org - CC BY 3.0 US	Adults on Hemlock sprig	Adelges tsugae (Hemlock woolly adelgid); adults on Hemlock sprig. USA.	©Tom Coleman/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Title Damage symptoms on Eastern hemlock Caption Hemlock woolly adelgid (Adelges tsugae); damage symptoms on Eastern hemlock (Tsuga canadensis). Joyce Kilmer area, North Carolina, USA. Copyright ©Jason Van Driesche/Bugwood.org - CC BY-NC 3.0 US	Damage symptoms on Eastern hemlock	Hemlock woolly adelgid (Adelges tsugae); damage symptoms on Eastern hemlock (Tsuga canadensis). Joyce Kilmer area, North Carolina, USA.	©Jason Van Driesche/Bugwood.org - CC BY-NC 3.0 US
Title Egg masses Caption Hemlock woolly adelgid (Adelges tsugae); egg masses on Tsuga sp. Laboratory photograph, Charlotte, North Carolina, USA. Copyright ©Lorraine Graney/Bartlett Tree Experts/Bugwood.org - CC BY-NC 3.0 US	Egg masses	Hemlock woolly adelgid (Adelges tsugae); egg masses on Tsuga sp. Laboratory photograph, Charlotte, North Carolina, USA.	©Lorraine Graney/Bartlett Tree Experts/Bugwood.org - CC BY-NC 3.0 US

Identity

Preferred Scientific Name

• Adelges tsugae Annand

Preferred Common Name

• hemlock woolly adelgid

Other Scientific Names

• Chermes tsugae Annand

International Common Names

• French: puceron lanigère de la pruche

Local Common Names

• Germany: Laus, Hemlockstannen; Tannenlaus, Hemlocks-

EPPO code

• ADLGTS (Adelges tsugae)

Summary of Invasiveness

The hemlock woolly adelgid (Adelges tsugae) is a small, aphid-like insect that has become a serious pest of eastern hemlock and Carolina hemlock. The most obvious sign of infestation is the presence of white, woolly egg masses on the underside of hemlock needles. Infested eastern North American hemlocks defoliate prematurely and will eventually die if left untreated. A. tsugae is a difficult insect to control as the white waxy secretion protects it from pesticides. It is dispersed to new habitats through the nursery trade and locally by wind, birds, mammals and humans. Hemlock trees provide important habitats for many wildlife species and A. tsugae has severe adverse ecological impacts which will become more severe as its distribution expands. Explanations for the rapid and invasive expansion of A. tsugae include a lack of natural enemies, a lack of resistance or tolerance to infestation by eastern hemlock and Carolina hemlock, and large reproductive output (Trotter and Shields, 2009).

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Hemiptera
•                         Suborder: Sternorrhyncha
•                             Unknown: Aphidoidea
•                                 Family: Adelgidae
•                                     Genus: Adelges
•                                         Species: Adelges tsugae

Description

Adelges tsugae is a small (0.74mm), reddish-purple, aphid-like insect that covers itself with a white, waxy secretion. Both winged and wingless forms are present. Their mouthparts are thread-like and about 1.5mm long and used to suck sap. Eggs are brownish-orange but darken as the embryo matures. When the eggs hatch, reddish-brown crawlers move about actively in search of a suitable site to settle. The tiny crawlers can only be seen with a hand lens as they are barely visible to the naked eye. Once the crawlers settle, they insert their mouthparts into the plant at the base of the hemlock needles and remain in the same place for the duration of their life. Dormant first instar nymphs are black with a white fringe around the edge and down the centre of the back. The developing nymphs produce white, cottony, waxy tufts that cover their bodies. The white masses are 3mm or more in diameter. The presence of these masses on the twigs and bark of hemlock is a sure sign of A. tsugae.

Distribution

Native range: China and Japan. A. tsugae were first described in western North America in 1924 and may be native to western North America (Havill and Footitt, 2007; US Forest Service, 2012).

Introduced range: Unintentionally introduced to eastern USA from Japan sometime before 1951, when it was first documented on ornamental hemlocks in Richmond, Virginia. Initially a pest of ornamental hemlock, but in the 1980s, A. tsugae was recognized as a threat to eastern and Carolina hemlocks as populations moved north through New Jersey, Long Island, and southern Connecticut and ultimately all of New England (Trotter and Shields, 2009). For distribution maps see the US Forest service website on hemlock woolly adelgid.

A. tsugae have moved south almost twice as fast as they have moved north, and some have linked this with a potential role of low temperatures in limiting the expansion of populations (Trotter and Shields, 2009).
 

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Habitat

The secondary host of Adelges tsugae is hemlock (where the asexual cycle occurs), and spruce is the primary host where the sexual cycle occurs. Experts hope that an aversion to cold weather will slow or stop its northern movement. In New Jersey and Connecticut, a large population of Adelges tsugae died as a result of a cold period in the winter of 2000.

Habitat List

Hosts/Species Affected

Some of the adults produced during the spring generation are winged individuals that are unable to reproduce on hemlock, therefore they leave the hemlock tree in search of spruce, the alternate host. But because no suitable spruce host is available in North America, they soon die. Hemlocks growing in poor conditions (compacted soils, ledgy soils, poor drainage, drought prone, etc.) are much more likely to succumb within 3-5 years from invasion. Hemlocks growing under better growing conditions have been shown to withstand infestations longer.

Host Plants and Other Plants Affected

Biology and Ecology

Nutrition
The hemlock woolly adelgid (Adelges tsugae) utilizes hemlock as its secondary host, where the asexual cycle occurs and spruce as its primary host, where the sexual cycle occurs. In North America the sexual cycle has not been previously recorded. Young twigs are the preferred feeding sites. Immature nymphs and adults feed on trees by sucking sap from the twigs. They attach themselves just below the base (abscission layer) of newly developed needles and feed on xylem parenchyma cells (tissue that manufactures and stores plant food).

Reproduction
A. tsugae has both sexual and asexual (parthenogenic) reproduction. In its native range the asexual cycle occurs on hemlock while the sexual stage occurs on spruce. However, because of a lack of suitable spruce species to act as a host, in its introduced range, A. tsugae has two asexual generations per year on hemlock (Trotter and Shields, 2009). Each adult can produce between 50-300 eggs within its lifetime. The large reproductive output of hemlock woolly adelgid contributes towards its invasive expansion (see also ‘Summary of Invasiveness’ section for explanations of invasiveness).

Lifecycle stages
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 (no feeding) until fall (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.
 

Natural enemies

Means of Movement and Dispersal

Introduction pathways to new locations
Forestry:
Nursery trade:Adelges tsugae was inadvertently shipped to Maine from Connecticut on untreated nursery stock in 1999.
Other:Adelges tsugae was accidentally introduced to the North American continent earlier this century (McClure 1987).

Local dispersal methods
Garden escape/garden waste:
Hikers' clothes/boots: Humans can disperse the insect through recreational activities.
Horticulture (local):Adelges tsugae can be spread via infested nursery stock (Ward et al. 2004).
On animals: The eggs and nymphs can be readily dispersed by birds, deer and other mammals.
On animals (local): The eggs and nymphs can be readily dispersed by birds.
On animals (local): The eggs and nymphs, which are not attached to the plant via mouthparts can be readily dispersed by wind.
People sharing resources (local): Humans can also disperse the insect through various activities, including logging and recreational activities.
Road vehicles: Humans can disperse the insect through recreational activities.

Pathway Causes

Pathway Vectors

Plant Trade

Impact Summary

Impact

General Impacts

The hemlock woolly adelgid (Adelges tsugae) is damaging hemlock ecosystems in eastern North America where both eastern hemlock (see Tsuga canadensis in IUCN Red List of Threatened Species) and Carolina hemlock (T. caroliniana) serve as hosts. To date, approximately 25% of the 1.3 million hectares of host type has been infested. The entire range of eastern hemlock is at risk within the next 20 to 30 years. Immature nymphs as well as adults damage trees by sucking sap from the twigs. The trees lose vigour and prematurely drop their needles, to the point of defoliation, which may lead to death. If left uncontrolled, the adelgids can kill a tree within three to four years. Trees of all sizes and ages are attacked, but natural stands of hemlock are at greatest risk for death. The value of ornamental hemlocks is reduced by the presence of the dirty, white woolly masses attached to the twigs or base of needles. Eastern hemlock is economically important in several areas of the eastern United States. The nursery industry in North Carolina and Tennessee currently maintains approximately $34 million in hemlock growing stock. This industry is feeling the effects of A. tsugae in reduced sales of native hemlock for ornamental use.

Hemlock trees are ecologically important and provide a unique environment. Eastern hemlock trees can reach a lifespan of 900 years and this tree is a component of many old growth communities. The hemlock forest also provides nesting sites and a foraging habitat for Neotropical migratory bird species. For example, the Acadian flycatcher (Empidonax virescens) uses Eastern hemlock for nesting and populations are thought to be negatively affected by A. tsugae infestation in Appalachian riparian forests (Allen et al., 2009). In addition, lepidopterans, such as the hemlock angle (Semiothisa fissinotata), which feed solely on hemlocks, will be affected. Several threatened or endangered species of flora and fauna require hemlock forests to survive. These forests are normally stable and resistant to plant invasions, but the loss of hemlocks from such forests will greatly affect the microclimate and soil conditions. Large-scale hemlock die-offs will affect species diversity, vegetation structure, stand environmental conditions and ecosystem processes.  Numerous studies have suggested that A. tsugae and associated loss of hemlock trees can impact upon ecosystem processes such as nitrogen and carbon cycling (see Cobb, 2010; Nuckolls et al., 2009; Orwig et al., 2008; Hadley et al., 2008). The loss of hemlock trees from the forests can lead to increased dominance of deciduous hardwood species, which may in turn have ecosystem effects (Spalding and Rieske, 2010).

Threatened Species

Risk and Impact Factors

• Proved invasive outside its native range

• Ecosystem change/ habitat alteration
• Host damage
• Negatively impacts forestry
• Threat to/ loss of endangered species
• Threat to/ loss of native species

• Herbivory/grazing/browsing

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Management information

Bibliography

References from GISD

Asaro, C., Berisford, C.W., Montgomery, M.E., Rhea, J. and Hanula, J. 2005. Biological control of the hemlock woolly adelgid in the Southern Appalachians. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Cheah, C.A.S-J., Mayer, M.A., Palmer, D., Scudder, T. and Chianese, R. 2005. Assessments of biological control of hemlock woolly adelgid with Sasajiscymnus tsugae in Connecticut and New Jersey. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Conway, H., Culin, J.D. and Hedden, R. 2004. Introduced biological control agents for hemlock woolly adelgid (HWA). Clemson University Entomology Insect Information Series.

Cowles, R.S. Soil application of imidacloprid to control hemlock woolly adelgid: best management practices. USDA Forest Service, Hemlock Woolly Adelgid website: Chemical control.

Cowles, R.S., Cheah, C. S-J. and Montgomery, M.E. 2005. Comparing systemic imidacloprid application methods for controlling hemlock woolly adelgid. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Evans, R.A. 2002. Hemlock ecosystems and Hemlock Woolly Adlegid at Delaware Water Gap National Recreation Area.

Felton, K. and Onken, B. 2006. Life stages of the hemlock woolly adelgid in the northern range. Prepared by USDA Forest Service, Forest Health Protection, Morgantown, West Virginia.

Havill, N.P. 2005. Using mitochondrial DNA to determine the native range of the Hemlock Woolly Adelgid. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Jefts, S. and Orwig, D. 2005. The effects of HWA outbreaks on ecosystem level changes in Southern New England. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Johnson, K., Taylor, G. and Remaley, T. 2005. Managing hemlock woolly adelgid and balsam woolly adelgid at Great Smoky Mountains National Park. In:Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Mark S. McClure. 1998. Hemlock Woolly Adelgid, Adelges tsugae (Annand), The Connecticut Agricultural Experiment Station.

Mark S. McClure. Managing Hemlock Woolly Adelgid, City Trees - The Journal of The Society of Municipal Arborists, Vol 33, Number 6 November/December 1997.

McClure, M., Salom, S., Shields, K. 2001. Hemlock woolly adelgid. FHTET-2001-03.

McClure, M.S. 1997."Managing Hemlock Woolly Adelgid. City Trees - The Journal of The Society of Municipal Arborists. 33 (6) November/December 1997.

McClure, M.S. Undated. Hemlock Woolly Adelgid, Adelges tsugae (Annand). The Connecticut Agricultural Experiment Station.

Michigan Department of Agriculture. 2001. Hemlock woolly adelgid quarantine. Pesticide and Plant Pest Management Division. http://na.fs.fed.us/fhp/hwa/pdfs/miquar.pdf

Morisawa, T. 22 March 2000. "Hemlock Woolly Adelgid: Adelges tsugae Annand", University of California, Davis, The Nature Conservancy.

Morisawa, T., 2003, Hemlock Woolly Adelgid: Adelges tsugae Annand, University of California, Davis, The Nature Conservancy.

New Hampshire Division of Forests and Lands. 2001. Hemlock Wooly Adelgid. Concord, New Hampshire: Department of Resources and Economic Development.

New Hampshire Division of Forests and Lands. 2001. Hemlock Wooly Adelgid. Concord, New Hampshire: Department of Resources and Economic Development.

Onken, B.P. 2002. Hemlock Woolly Adelgid - a race in time. USDA Forest Service.

Orwig, D.A. and Kittredge, D. 2005. Silvicultural options for managing hemlock forests threatened by hemlock woolly adelgid. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Pais, R.C. and Polster, K.M. Undated. Strategies for Managing Hemlock Woolly Adelgid (Adelges tsugae) in Forests. EcoScientific Solutions LLC, 930 Meadow Avenue, Suite 2B, Scranton, PA 18505.

Plant Pest Surveillance Unit. 2005. Canadian Food Inspection Agency website. Adelges tsugae (Annand) - hemlock woolly adelgid.

Rabaglia, R.J. 2005. The Maryland hemlock woolly adelgid management plan. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005

Salom, S. M., 1999. Virginia Tech Department of Entomology. Hemlock Woolly Adelgid: A Major Threat to Eastern Hemlock, Virginia Forest Landowner Update. Spring 1999 -- Volume 13, No. 2 .

Salom, S.M. 1999. Hemlock Woolly Adelgid: A Major Threat to Eastern Hemlock. Virginia Forest Landowner Update. Spring 1999. 13 (2). Virginia Tech Department of Entomology.

Salom, S.M., M.S. McClure, M.E. Montgomery, G. Zilahi-Balogh, L.T. Kok 2001. Hemlock woolly adelgid in the United States: status of on-going biological control efforts.

Salom, S.M., McClure, M.S., Montgomery, M.E., Zilahi-Balogh, G., and Kok, L.T. 2001. Hemlock woolly adelgid in the United States: status of on-going biological control efforts. pp. 87-97. In: IUFRO World Series Vol. 11. Protection of world forests from insect pests: advances in research. Proceedings of the XXI IUFRO World Congress 7-12 August 2000, Kuala Lumpur, Malaysia

Snyder, C.D., Young, J.A., Ross, R.M. and Smith, D.R. 2005. Long-term effects of hemlock forest decline on headwater stream communities. In: Onken, B. and Reardon, R. (Compilers). 2005. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States. Asheville, North Carolina. February 1-3, 2005.

Strategies for Managing Hemlock Woolly Adelgid (Adelges tsugae) in Forests Richard C. Pais and Kathleen M. Polster EcoScientific Solutions LLC 930 Meadow Avenue, Suite 2B, Scranton, PA 18505

USDA Forest Service, 2006. Northeastern area. Hemlock wooly adelgid http://na.fs.fed.us/fhp/hwa/

USDA Forest Service. 2004. Biological control of hemlock woolly adelgid. USDA Forest Service FHTET-2004-04. http://www.invasive.org/hwa/index.cfm

USDA Forest Service. 2004. Number of beetles released and release sites by state.

USDA Forest Service. 2006. List of state and counties with known Hemlock Woolly Adelgid infestations. Prepared by USDA Forest Service, Forest Health Protection, Morgantown, West Virginia.

USDA Forest Service., 2008. Hemlock Woolly Adelgid website. Northeastern Area Forest Health Protection http://www.na.fs.fed.us/fhp/hwa/

USDA National Agricultural Library., 2006. National Invasive Species Information Centre Species profiles Hemlock wooly adelgid. http://www.invasivespeciesinfo.gov/animals/hwa.shtml

USDA. 3 June 2002, " Hemlock Woolly Adelgid Management ", USDA Forest Service - Northeastern Area.

Ward, J.S., Montgomery, M.E., Cheah, C.A.S-J., Onken, B.P. and Cowles, R.S. 2004. Eastern hemlock forests: Guidelines to minimize the impacts of hemlock woolly adelgid. USDA Forest Service, Northeastern Area State and Private Forestry, Morgantown, West Virginia.

Webb, R.E., Frank, J.R. and Raupp, M.J. 2003. Eastern hemlock recovery from Hemlock Woolly Adelgid damage following imidacloprid therapy. Journal of Arboriculture. 29 (5): 298-302.

References

Allen MC, Sheehan J Jr, Master TL, Mulvihill RS, 2009. Responses of Acadian Flycatchers (Empidonax virescens) to Hemlock Woolly Adelgid (Adelges tsucae) infestation in Appalachian riparian forests. Auk, 126(3):543-553. http://www.bioone.org/doi/full/10.1525/auk.2009.08073

Cobb RC, 2010. Species shift drives decomposition rates following invasion by hemlock woolly adelgid. Oikos, 119(8):1291-1298. http://www.blackwell-synergy.com/loi/oik

Cook S, Humes K, Hruska R, Williams C, Fraley G, 2010. Previsual detection of two conifer-infesting adelgid species in North American forests. In: General Technical Report - Pacific Northwest Research Station, USDA Forest Service, No.PNW-GTR-802(2) [ed. by Pye, J. M.\Rauscher, H. M.\Sands, Y.\Lee, D. C.\Beatty, J. S.]. Portland, USA: Pacific Northwest Research Station, USDA Forest Service, 551-558.

Dhungel EK, Groninger JW, Holzmueller EJ, 2010. Tree species and environment associations within hemlock-silverbell stands treated for hemlock woolly adelgid in Great Smoky Mountains National Park. Journal of the Torrey Botanical Society, 137(4):401-409. http://www.torreybotanical.org/journal.html

Fajvan MA, 2008. The role of silvicultural thinning in eastern forests threatened by hemlock woolly adelgid (Adelges tsugae). General Technical Report - Pacific Northwest Research Station, USDA Forest Service [Integrated restoration of forested ecosystems to achieve multiresource benefits: Proceedings of the 2007 National Silviculture Workshop, Ketchikan, Alaska, USA, 7-10 May 2007.], No.PNW-GTR-733:247-256.

Forest Service US, 2012. Northeastern Area. Forest Health Protection - Hemlock Woolly Adelgid. Distribution Maps. http://na.fs.fed.us/fhp/hwa/maps/distribution.shtm.

Forest Service US, 2012. Northeastern Area. Forest Health Protection - Hemlock Woolly Adelgid. http://www.na.fs.fed.us/fhp/hwa/.

Hadley JL, Kuzeja PS, Daley MJ, Phillips NG, Mulcahy T, Singh S, 2008. Water use and carbon exchange of red oak- and eastern hemlock-dominated forests in the northeastern USA: implications for ecosystem-level effects of hemlock woolly adelgid. Tree Physiology [Regional forest responses to environmental change, a IUFRO travelling workshop held in New Hampshire, Massachusetts and New York, USA, 6-13 October 2006.], 28(4):615-627. http://heronpublishing.com

Havill NP, Foottit RG, 2007. Biology and evolution of Adelgidae. Annual Review of Entomology, 52:325-349. http://www.annualreviews.org

ISSG, 2011. Global Invasive Species Database (GISD). Invasive Species Specialist Group of the IUCN Species Survival Commission. http://www.issg.org/database

Mausel DL, Driesche RGvan, Elkinton JS, 2011. Comparative cold tolerance and climate matching of coastal and inland Laricobius nigrinus (Coleoptera: Derodontidae), a biological control agent of hemlock woolly adelgid. Biological Control, 58(2):96-102. http://www.sciencedirect.com/science/article/pii/S1049964411000880

Mausel DL, Salom SM, Kok LT, Davis GA, 2010. Establishment of the hemlock woolly adelgid predator, Laricobius nigrinus (Coleoptera: Derodontidae), in the eastern United States. Environmental Entomology, 39(2):440-448. http://www.bioone.org/doi/full/10.1603/EN09088

Montgomery ME, Shiyake S, Havill NP, Leschen RAB, 2011. A new species of Laricobius (Coleoptera: Derodontidae) from Japan with phylogeny and a key for native and introduced congeners in North America. Annals of the Entomological Society of America, 104(3):389-401. http://docserver.ingentaconnect.com/deliver/connect/esa/00138746/v104n3/s3.pdf?expires=1306550229&id=0000&titleid=10263&checksum=EA6B2DAAC72485321B2320ED40B7D3E9

NAPPO, 2013. Phytosanitary Alert System: Detection and eradication of hemlock woolly adelgid (Adelges tsugae Annand) in Niagara Glen park, Ontario. Phytosanitary Alert System: Detection and eradication of hemlock woolly adelgid (Adelges tsugae Annand) in Niagara Glen park, Ontario. NAPPO. http://www.pestalert.org/oprDetail.cfm?oprID=554

Nuckolls AE, Wurzburger N, Ford CR, Hendrick RL, Vose JM, Kloeppel BD, 2009. Hemlock declines rapidly with hemlock woolly adelgid infestation: impacts on the carbon cycle of Southern Appalachian forests. Ecosystems, 12(2):179-190. http://springerlink.metapress.com/content/6616693064u73306/fulltext.pdf

Orwig DA, Cobb RC, D'Amato AW, Kizlinski ML, Foster DR, 2008. Multi-year ecosystem response to hemlock woolly adelgid infestation in southern New England forests. Canadian Journal of Forest Research, 38(4):834-843. http://cjfr.nrc.ca

Spaulding HL, Rieske LK, 2010. The aftermath of an invasion: structure and composition of Central Appalachian hemlock forests following establishment of the hemlock woolly adelgid, Adelges tsugae. Biological Invasions, 12(9):3135-3143. http://www.springerlink.com/content/r314k14r3v6268l2/

Trotter RT III, Shields KS, 2009. Variation in winter survival of the invasive hemlock woolly adelgid (Hemiptera: Adelgidae) across the eastern United States. Environmental Entomology, 38(3):577-587. http://www.bioone.org/doi/abs/10.1603/022.038.0309

US Fish and Wildlife Service, 1994. In: Shenandoah salamander (Plethodon shenandoah) Recovery Plan. US Fish and Wildlife Service, 36 pp..

USDA, 2012. Hemlock Woolly Adelgid. Release and Evaluation of Scymnus sinuanodulus. http://www.nrs.fs.fed.us/disturbance/invasive_species/hwa/control_management/release_scymnus_sinuanodulus/.

Vieira LC, McAvoy TJ, Chantos J, Lamb AB, Salom SM, Kok LT, 2011. Host range of Laricobius osakensis (Coleoptera: Derodontidae), a new biological control agent of hemlock woolly adelgid (Hemiptera: Adelgidae). Environmental Entomology, 40(2):324-332. http://docserver.ingentaconnect.com/deliver/connect/esa/0046225x/v40n2/s16.pdf?expires=1303714478&id=0000&titleid=10265&checksum=79795E41E45F4DAE0DE93B3E5D746542

Zilahi-Balogh GMG, Kok LT, Salom SM, 2005. A predator case history: Laricobius nigrinus, a derodontid beetle introduced against the hemlock woolly adelgid. Second International Symposium on Biological Control of Arthropods, Davos, Switzerland, 12-16 September, 2005. Washington, USA: United States Department of Agriculture, Forest Service, 651-664.

Distribution References

CABI, Undated. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI

Invasive Species Specialist Group (ISSG), 2011. Global Invasive Species Database (GISD). In: Global Invasive Species Database (GISD), Auckland, New Zealand: University of Auckland. http://www.issg.org/database

IPPC, 2020. Detection of Hemlock Woolly Adelgid (Adelges tsugae) at the Harold Mitchell Nature Reserve in Wainfleet, Ontario. In: IPPC Official Pest Report, Rome, Italy: FAO. https://www.ippc.int/

NAPPO, 2013. Phytosanitary Alert System: Detection and eradication of hemlock woolly adelgid (Adelges tsugae Annand) in Niagara Glen park, Ontario.,

Principal Source

Global Invasive Species Database

Contributors

Reviewed by: Gabriella (Riella) Zilahi-Balogh, PhD Entomologist/Entomologiste Programme Officer, Plant Health/agent de programme, protection des végétaux Canada

Principal sources:USDA Forest Service - Hemlock Woolly Adelgid website. Northeastern Area Forest Health Protection

Distribution Maps