The Balsam Woolly Adelgid

Adelges piceae - Phylloxeridae

Balsam Woolly Adelgid (wool removed)

The balsam woolly adelgid is an insect that infests Balsam and Fraser fur trees, killing a once healthy tree in only 3 to 4 years. This small, purple or bluish-black insect is native to central Europe, and its introduction to the United States in the early 1900s has caused a serious decline in fur populations throughout the Smoky Mountains. Since the BWA was noticed in Maine of 1908, if has felled billions of feet of fur timber in North America and is one of many introduced species that has negatively impacted its new environments because it has few natural predators. It appears as tiny (1 mm long) wooly dots on the bark of trees due to its covering of wax-like threads (1).

Reproduction

Adelgids reproduce by parthenogenesis, a type of asexual reproduction, forming only female eggs by mitosis without the fertilization by sperm (4). A female adlegid can lay a waxy mass of over 200 eggs in the spring and summer which develop into the only mobile life stage, the crawler. In this stage, they must find a fur to feed on for all adult life. While the insects feed with long, tube-like mouthparts, they secrete an irritating, salivary substance that illicits a defensive response from trees. This response produces more heartwood cells in the sapwood, swelling tissue and slowing nutrient, hormone, and water flow throughout the tree (2). Abnormal wood growth causes malformed stems and branches, especially damaging to the Fraser fur Christmas tree industry (3).

Dispersal

Spread of the balsam woolly aphid occurs during the egg, and newly hatched nymph or crawler stages. Experiments have shown crawlers to live over 8 days and to be capable of crawling more than 30 m. Eggs and crawlers fall or are blown down from infested crowns during the spring, summer and fall and may be carried on clothing, vehicles, tents and other equipment. They have been found in traps 90 m from infested stands and are probably capable of being carried many kilometers by wind currents. They are also carried by birds and animals. Movement of infested logs and nursery stock are other means of spread, the latter probably being the manner of most distant spread.

Control and Prevention

Control of this pest is naturally maintained by low winter temperatures and a beetle, Laricobius erichsonii(1), while costly chemical control is only used for economically important ornamentals and seed productions (4). Management techniques include clearing and burning infested trees, and lowering tree stress by maintaining a low density of trees per stand, adequate nutrient levels, and soil moisture (2).

References

(1) Balsam Wolly Adelgid - ipmwww.ncsu.edu/AG189/html/Balsam_Wolly_Adelgid.HTML

(2) Balsam Woolly Adelgid - www.ext.vt.edu/departments/entomology/factsheets/balwoade.html

(3) Christmas Tree Notes - www.ces.ncsu.edu/nreos/forest/xmas/CTN020.html

(4) Balsam Woolly Aphid - http://fhpr8.srs.fed.us/idotis/insects/bwa.htm

For more information on BWA control practices, see Christmas Tree Notes at www.ces.ncsu.edu/nreos/forest/xmas/CTN020.html