Balsam woolly adelgid

Written by V.G. Nealis Revision 2024

• French common name: Puceron lanigère du sapin
• Other common names: Balsam woolly aphid
• Scientific name: Adelges piceae (Ratzeburg)
• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Hemiptera
• Family: Adelgidae
• Partial list of synonyms:
  • Chermes piceae Ratzeburg  
  • Dreyfusia piceae Ratzeberg

General information and importance

Adelgids are a distinct group of small (adults less than 2 millimetres), soft-bodied, pear-shaped insects related to aphids. They are specialist feeders on conifers in the Pinaceae family (pine (Pinus), spruce (Picea), fir (Abies), hemlock (Tsuga), larch (Larix), and Douglas-fir (Pseudotsuga menziesii)) and inhabit boreal and temperate forests of North America and Eurasia. Feeding adelgids exude a white, waxy flocculent material that covers their bodies and gives them their common name, “woolly adelgids”. Several species have been accidentally introduced from Europe and Asia to North America where they have become forest pests.

Adelgids have complex life histories. There may be a two-year life cycle with a sexual generation on a primary host (usually spruce), followed by dispersal to an alternate, secondary host (a conifer species in a different genus) where they reproduce asexually for the second season before returning to the primary host. Alternatively, adelgids may reproduce asexually for several generations on a secondary host exclusively. This life cycle requires only one year. Newly hatched nymphs are called “crawlers” and often are the only actively mobile stage in the life cycle. Once settled at a feeding site, the adelgid nymph remains in this location for the duration of its life. All stages feed by inserting piercing mouthparts (stylets) into tree tissues, injecting saliva, and sucking up nourishment. On primary hosts, feeding induces formation of galls. On secondary hosts, feeding causes distortion and eventual loss of needles, twigs, and/or stems near the feeding site. In all cases, feeding interferes with healthy function of the tree.

Balsam woolly adelgid is native to the spruce-fir forests of Europe. The taxonomy of this insect and a few other closely related species in Europe and Asia is under investigation because of the complexities in their life cycles, host alternation, and hybridization in the complex of species. In its native range, balsam woolly adelgid causes minimal serious damage. It was first found in northeastern forests of North America in 1908, likely introduced on nursery stock at several locations before 1900. It has since spread throughout the northeastern United States and Atlantic Canada. Balsam woolly adelgid was detected in California in 1928 and now occurs throughout the Pacific Northwest. The first damage in western Canada was noted near Vancouver in 1958 and balsam woolly adelgid has since spread slowly in the south coastal region of British Columbia. In 2015, infestations were confirmed in the interior forests of British Columbia, including the Okanagan, Kootenay, and Cariboo regions. Visible damage across more than 5000 ha of forest occurred in British Columbia in 2020. In its introduced North American range, balsam woolly adelgid occurs only on true firs.

Distribution and hosts

Balsam woolly adelgid is native to Europe and was introduced to northeastern North America in the late 19^th century. It now occurs through higher elevation Appalachian forests in the United States to Tennessee and north through the Atlantic provinces of Canada, including Newfoundland and Labrador. It was recently found in Michigan. Independent introductions to northern California were discovered in 1928 with subsequent spread through the Pacific Northwest to coastal British Columbia as far north as the Great Bear Rainforest. Isolated populations have been found recently in the southern interior of British Columbia, including the Thompson and Okanagan valleys.

North American species of true fir, especially balsam fir (Abies balsamea) in eastern Canada and subalpine fir (A. lasiocarpa) in western Canada, are most vulnerable. Amabilis fir or Pacific silver fir (A. amabilis) and grand fir (A. grandis) in western Canada are less vulnerable. The most damaging outbreaks occur in mild, moist, maritime forests of the Atlantic and Pacific coasts. Cold winters appear to have limited expansion of its range north and to higher elevations in both Atlantic Canada and British Columbia. In its native range in Europe, the insect feeds on European silver fir (A. alba).

Host parts affected

The insect feeds on bark cortex on all parts of the tree (root collars, bole, branches, and twigs) as well as new buds. Balsam woolly adelgid infestations concentrate on boles and branches where they tend to cause more tree mortality.

Symptoms and signs

Adult balsam woolly adelgids are small (less than 2 millimetres), wingless, nearly spherical, and rusty brown to purplish black. There are no males. Female adults are most easily detected by the white wool-like threads they produce to cover their bodies and eggs. Eggs are amber to rusty brown. The tiny (1 millimetre), newly hatched, mobile “crawlers” have longer legs and antennae than subsequent stages. They soon become sedentary at their selected feeding sites. The woolly covering of the adelgid on branch nodes at the base of needles and in bark fissures is the most obvious direct evidence of the insect.

First evidence of infestation is distortion of new growth. Needles turn red. After a few years of infestation, shoots become swollen. This symptom is known as “gouting” and leads to branch dieback beginning at the top of the crown. The top of the crown sometimes breaks off, giving the tree a funnel-like appearance. Eventually, the entire tree may die.

Life cycle

Balsam woolly adelgid spends its entire life cycle on a single fir-tree host, where it reproduces parthenogenetically. There are no males and winged forms are rare. The insect is multivoltine, with two or three generations per year in Atlantic Canada and three or four generations in British Columbia depending on local seasonal temperatures.

Balsam woolly adelgids overwinter as first-stage nymphs that hatch from eggs laid by adults the previous autumn. These tiny “crawlers” may move several metres before selecting a feeding site, inserting their stylets into the bark cortex and settling into the location they will occupy for the remainder of their lives. First generation adults mature and lay eggs in May. The final generation of adults mature and lay eggs in August. Natural dispersal to new trees by the crawler stage is limited, therefore adelgid populations tend to become very dense on trees once infested. When dispersal does occur, it tends to be via wind and animals. It can sometimes occur across long distances (e.g., during bird migration in spring).

Damage

Balsam woolly adelgid infests all age classes of true fir trees. It caused significant mortality of balsam fir in Atlantic Canada following its introduction in the 1940s. This insect has been linked to the decline of Fraser fir (Abies fraseri) and balsam fir in the eastern United States. In British Columbia, balsam woolly adelgid is a pest of amabilis fir in coastal forests.

Damage becomes apparent in the upper crown of trees soon after significant populations become established. Feeding adelgids inject salivary compounds, which interfere with normal translocation of water and nutrients causing distortion of growing shoots. Twigs swell at the nodes resulting in characteristic gout. Needles discolour and drop. Eventually, branches die back reducing the crown profile. There is also internal damage as trees produce irregular growth rings with brittle, lignified wood, reducing the commercial value of the fibre. As the infestation spreads throughout the tree, death may occur as quickly as two to three years. Because the insect is multivoltine, climate change may facilitate more generations per year and limit overwintering mortality, both of which would be expected to lead to more severe impacts on tree health.

Prevention and management

Pest management strategies for a particular pest vary depending on several factors. These include:

• the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
• the expected damage or other negative consequences of the pest’s activity and population level (either to the host, property, or the environment);
• an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
• how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
• the value of the host(s) versus the costs of pest management approaches; and
• consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.

Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any particular pest.

An extensive biological control program targeting balsam woolly adelgid from the 1930s through the 1980s failed to control the insect. There have been no recent attempts to introduce agents or determine the fate or impact of agents released during the earlier programs.

In British Columbia, quarantines restricting the movement of live nursery stock and Christmas trees appeared to have slowed the spread of balsam woolly adelgid for many years, although climatic conditions outside the regulated areas have also been less favourable to the insect. The recent expansion of balsam woolly adelgid to interior forests likely indicates improving winter conditions for the adelgid and may make containment by quarantine more difficult.

Many different chemical insecticides have been tested against balsam woolly adelgid. Effective results were obtained in seed orchards, Christmas tree production, and nurseries where insecticides could be applied at relatively high concentrations and volumes. However, these rates are not practical in forest settings.

Pesticides registered for use against balsam woolly adelgid under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered pesticides and product information for use against this insect. The application of any registered product should be based on population size and applied only when necessary and against the approved life stage. It is also recommended to consult a local tree care professional. Pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and follow all directions and precautions noted on the manufacturer’s label. In some jurisdictions and situations, only a licensed professional can apply pesticides. Consulting relevant local authorities to determine local regulations that are in place is recommended.

Selected references

Adam, C.I.; Ostaff, D.P. 2006. Balsam woolly adelgid. Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre. Fredericton, New Brunswick. Pest Notes No. 3. 2p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/77dda367-d571-410a-bf60-4b98002f4622?fromSearchPage=true

Duncan, R.W. 1996. Common woolly aphids and adelgids of conifers. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Forest Pest Leaflet 19. 8 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/9d25485b-a4d9-4b1b-bdf5-2a12441a63ed?fromSearchPage=true

Greenbank, D.O. 1970. Climate and the ecology of the balsam woolly aphid. The Canadian Entomologist 102(5): 546–578. https://doi.org/10.4039/Ent102546-5

Havill, N.P.; Griffin, B.P.; Andersen, J.C.; Foottit, R.G.; Justesen, M.J.; Caccone, A.; D’Amico, V.; Elkinton, J.S. 2021. Species delimitation and invasion history of the balsam woolly adelgid, Adelges (Dreyfusia) piceae (Hemiptera: Aphidoidea: Adelgidae), species complex. Systematic Entomology 46(1): 186–204. https://doi.org/10.1111/syen.12456

Hollingsworth, R.G.; Hain, F.P. 1991. Balsam woolly adelgid (Homoptera: Adelgidae) and spruce-fir decline in the southern Appalachians: assessing pest relevance in a damaged ecosystem. The Florida Entomologist. 74(2): 179–187. https://doi.org/10.2307/3495294

Quiring, D.; Ostaff, D.; Hartling, L.; Lavigne, D.; Moore, K.; DeMerchant, I. 2008. Temperature and plant hardiness zone influence distribution of balsam woolly adelgid damage in Atlantic Canada. The Forestry Chronicle 84(4): 558–562. https://doi.org/10.5558/tfc84558-4

Schooley, H.O.; Harris, J.W.E.; Pendrel, B. 1984. Adelges piceae (Ratz.) balsam woolly adelgid (Homoptera: Adelgidae). Pages 229-234 in J.S. Kelleher and M.A. Hulme, editors. Biological control programmes against insects and weeds in Canada 1969–1980. Commonwealth Agricultural Bureaux. Farnham, United Kingdom.

Smith, G.F.; Nicholas, N.S. 1998. Patterns of overstory composition in the fir and fir-spruce forests of the Great Smoky Mountains after balsam woolly adelgid infestation. The American Midland Naturalist. 139(2): 340–352. https://www.jstor.org/stable/2426691

Turnquist, R.; Harris, J.W.E. 1993. Balsam woolly adelgid. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Forest Pest Leaflet 1. 4 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/24a186d2-6dcc-4414-ac11-cdf3f425317e?fromSearchPage=true

Zilahi-Balogh, G.M.G., Humble, L.M., Foottit, R., Burleigh, J. and Stock, A. 2016. History of the balsam fir woolly adelgid, Adelges piceae (Ratzeburg), in British Columbia with notes on a recent range expansion. Journal of the Entomological Society of British Columbia. 113: 21–38. Available at: https://journal.entsocbc.ca/index.php/journal/article/view/923

Cite this fact sheet

Photos

Damaged and galled balsam fir twig attacked by balsam woolly adelgid.

Jean-Paul Laplante

Characteristic swelling of balsam fir twigs after a recent attack by balsam woolly adelgid on the tree crown.

Jean-Paul Laplante

Close-up of the white woolly wax covering balsam woolly adelgids on a balsam fir trunk.

Thérèse Arcand

Aerial view of a damaged, mature, balsam fir forest that has been infested by balsam woolly adelgid for several years.

Robert Blais

A mature balsam fir with red needles resulting from a severe attack on its trunk by balsam woolly adelgid.

René Martineau

Balsam fir crowns damaged by balsam woolly adelgid.

Claude Monnier

Balsam fir trunk covered with white woolly wax secreted by balsam woolly adelgid.

Claude Monnier

Close-up of balsam fir top damaged by balsam woolly adelgid.

Claude Monnier

Balsam fir trunk covered with white woolly wax secreted by balsam woolly adelgid. A section of bark has been removed to show the underlying damage.

Claude Monnier

Balsam fir crowns affected by the balsam woolly adelgid.

Robert Gagnon