By East Kootenay Invasive Species Council

The Balsam wooly adelgid (BWA) is a small, sap-sucking wingless insect native to Europe that feeds on true Firs. BWA damage trees by feeding. As they drink sap through their straw-like mouthparts, they inject saliva which is toxic to the tree. The saliva causes swelling around the feeding area, which compresses the wood and kills terminal buds. This swelling, called tree gout, will hinder growth, cause needles to yellow and drop, plus may kill the crown of a tree. It also reduces wood quality. By killing needles and preventing new growth, adelgid feeding can kill a tree within a few years.

How to Identify:

Adult Balsam wooly adelgids resemble aphids. They are around one mm across and grey, with a white waxy sheen.

These insects have between two to four generations per year. Female adelgids lay up to 200 brown eggs under white woolly tufts of wax along tree trunks and branches. In a heavily infested tree, the trunk may be covered with these tufts. The eggs hatch into an immature ‘crawler’ which disperses throughout the tree and to new host trees. These crawlers are about one-third the size of an adult Balsam wooly adelgid, with an amber coloured oval body.

Impacts:

Tree Mortality: Causes significant tree death, especially in Fraser fir, balsam fir, and other fir species.

Forest Composition Changes: Alters forest structure, reducing fir populations and increasing other species like red spruce and yellow birch.

Loss of Habitat: Threatens unique habitats for species like the spruce-fir moss spider and certain lichen.

Disrupted Ecosystem Dynamics: Affects understory vegetation, leading to changes in plant species composition.

Wildlife Displacement: Impacts bird populations and other wildlife dependent on fir forests.

Altered Successional Pathways: In the West, BWA disrupts forest regeneration and changes the natural succession of species in certain environments (e.g., alpine meadows, avalanche chutes).

Hydrological Effects: Loss of fir trees can affect water retention, snowmelt, and stream flow characteristics.

Increased Fire Risk: Dead trees contribute to higher fuel loads, increasing fire danger.

Reduced Reproduction: Surviving trees suffer from crown dieback, diminished seed production, and increased susceptibility to other pests.

Deteriorated Water Quality: Loss of tree canopy along streams impacts water quality and fish populations downstream.

Increased Pest Vulnerability: Surviving trees are more vulnerable to secondary pests like bark beetles.

Learn more.

East Kootenay Invasive Species Council images

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