Eastern spruce gall adelgid

Written by V.G. Nealis Revision 2024

• French common name: Puceron à galle conique de l'épinette
• Other common names: pineapple gall adelgid, spruce gall aphid
• Scientific name: Adelges abietis (Linnaeus)
• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Hemiptera
• Family: Adelgidae
• Partial list of synonyms:
  • Adelges gallarumabietis De Geer
  • Chermes abietis Linnaeus    
  • Sacciphantes abietis Linnaeus

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.

Eastern spruce gall adelgid is native to Europe and was likely introduced to North America in the 19^th century. In Canada, it has been recorded feeding on every spruce species in the northern forests from Atlantic to Pacific coasts. Galls induced on spruce trees by this adelgid are sometimes called pseudocones, as they superficially resemble actual spruce cones but are much smaller (1.5 to 3 centimetres). The common name, pineapple gall adelgid, refers to the resemblance of the gall to a tiny pineapple.

Distribution and hosts

In Canada, eastern spruce gall adelgid occurs from the Atlantic to Pacific coasts but is most common in eastern forests. It is established throughout the Appalachian region of the United States from Tennessee to Maine and in localized pockets in central and western states adjacent to Canada. Eastern spruce gall adelgid has been recorded from every spruce species in Canada. However, most damage occurs on introduced Norway spruce (Picea abies) and native white spruce (P. glauca) in eastern Canada and Sitka spruce (P. sitchensis) in western Canada.

Host parts affected

Galls form from swellings at the base of needles. Shoots can continue to grow beyond the position of the gall on the shoot.

Symptoms and signs

Adelgids are tiny insects and difficult to see with the naked eye. The waxy, white flocculent material exuded by feeding stages is usually the first indication of their presence. Eastern spruce gall adelgid in North America forms small (1.5 to 3 centimetres), pineapple-shaped galls on its primary spruce hosts. These galls are the most easily observed diagnostic characteristic of this species.

Life cycle

Eastern spruce gall adelgid is unusual among adelgids because it has a one-year life cycle with no sexual stages on the primary spruce host. There are no secondary hosts or males in its introduced range. All reproduction is asexual (parthenogenesis). The adelgid overwinters as an immature fundatrix or “founding mother” attached to twigs at the base of new buds. It matures in early spring and lays eggs surrounded by waxy covering. Crawlers hatch from the eggs and settle at the base of the needles, which are already swollen because of previous feeding by their mothers. As the nymphs feed, they induce formation of the gall, which eventually contains about 12 feeding nymphs. The nymphs complete their development by late summer, leave the desiccated gall and develop wings. However, these winged adults are feeble flyers and usually remain on the same tree. Their eggs become the next generation of fundatrices to complete the life cycle.

Damage

Galls formed by eastern spruce gall adelgid are the main type of damage. When populations are very dense, the galls can be unsightly on ornamental spruces and Christmas trees and even cause some die-back. Discolouration of needles and distortion of shoots also reduce amenity values. Tree mortality is uncommon, as galls do not prevent the tree from realizing continued growth, even on infested shoots.

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.

Pruning out and destroying galls while they are still green and before adelgids emerge is an effective practice in nurseries when populations are not too high and the number of host trees affected is relatively low. The presence and density of eastern spruce gall adelgid have not been significantly reduced by biological control programs.

Insecticide applications are not warranted in forest situations. Heavy infestations in spruce seed orchards, Christmas tree plantations, and ornamental plantings may require insecticide treatment. Pesticides registered for use against eastern spruce gall 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

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.

Havel, N.P.; Foottit, R.G. 2007. Biology and evolution of Adelgidae. Annual Review of Entomology 52: 325–349. https://doi.org/10.1146/annurev.ento.52.110405.091303

Rose, A.H.; Lindquist, O.H. 1985. Insects of eastern spruces, fir and hemlock. Canadian Forestry Service, Headquarters, Science Branch. Ottawa, Ontario. Forestry Technical Report 23. 159 p.

Smith, C.C.; Newell, W.R. 1972. Eastern spruce gall aphid. Environment Canada, Canadian Forestry Service, Maritimes Forest Research Centre. Fredericton, New Brunswick. Pest Leaflets.

Cite this fact sheet

Photos

An eastern spruce gall adelgid egg mass deposited at the base of needles and protected by white, waxy flocculence.

Thérèse Arcand

A cross-section of a young gall that has been cut in half, revealing the interior chambers where immature adelgids are feeding.

Thérèse Arcand

Close-up of an eastern spruce gall adelgid adult, wings folded.

Thérèse Arcand

Close-up of an eastern spruce gall adelgid adult, wings spread.

Thérèse Arcand

A developing, pineapple-shaped gall caused by eastern spruce gall adelgid on a new white spruce shoot.

Thérèse Arcand

Eastern spruce gall adelgid egg masses deposited at the base of needles but with some of the protective silk waxy flocculence removed from one egg mass to reveal the eggs.

Thérèse Arcand

Chambers of a gall on white spruce that have opened to allow eastern spruce gall adelgid adults to emerge. Several adults are visible near the gall.

Thérèse Arcand

Old galls caused by eastern spruce gall adelgid that have started to dry and discolour.

Thérèse Arcand

New white spruce shoots bearing developing galls caused by eastern spruce gall adelgid.

Thérèse Arcand

White spruce branch bearing several old, dry galls caused by eastern spruce gall adelgid.

Thérèse Arcand

Developing gall on a Norway spruce shoot caused early in the growing season by eastern spruce gall adelgid.

Thérèse Arcand

Developing gall on a white spruce shoot caused early in the growing season by eastern spruce gall adelgid.

Thérèse Arcand

An old, dry gall caused by eastern spruce gall adelgid. Note that the twig beyond the gall has also died.

Thérèse Arcand