Adelges piceae

Adelges piceae (Ratzeburg)

Healthy fir	Dead firs I	Dead firs II	Dead firs III
Adelgid eggs	Adelgid (crawler)	Leaf infestion	Trunk infestation	Infestation (close view)

Balsam woolly adelgid
The balsam woolly adelgid was introduced to New England in 1908 (Kotinsky, 1916) and the western states in 1928 (Annand, 1928) on nursery stock from Europe. The pest attacks all North American true fir species (Abies), with the possible exception of the divergent bristlecone fir (A. bracteata). Abnormal tissue development occurs due to salivary secretions during feeding, which change the balance of plant growth hormones and inhibitors (Balch et al., 1964). It is believed that a combination of factors associated with salivary secretions kills the plant tissue (Hay, 1978). The pest can damage and even kill western fir species and balsam firs (A. balsamea) in eastern forests (Mitchell & Buffam, 2001).

The greatest mortality, however, is in the southern Appalachians where it kills mature specimens of Fraser fir (A. fraseri). Fraser fir is restricted to mountaintop environments in the southern Appalachians, where the species forms a unique forest type with red spruce (Picea rubens). Mortality is variable among mountaintops, with fewer than ten mature trees surviving on some mountains, although many immature trees also persist. However, the reproductive potential of this species could be in jeopardy. Smith & Nicholas (2000) studied Fraser fir size and age class distributions and found lower densities of young firs in stands severely impacted by adelgids. They attributed the lower tree densities to low numbers of reproducing adult trees, competition, and other environmental factors.

The adelgid was first noticed on a northern population of Fraser fir in 1957, and it subsequently spread to all populations (Johnson, 1980). Infested trees usually die within seven years (Johnson, 1980). A study on Mt. Guyot, Tennessee, in the Great Smoky Mountains National Park revealed that Fraser fir declined from 80% to 2.5% of living crown trees in the time period of 1967-1985 (Alsop & Laughlin, 1991). This demise resulted in a dramatic change in forest composition and dynamics on former Fraser fir sites. With the forest canopy removed, the understory changed from primarily blueberry (Vaccinium) and fir saplings to dense blackberry (Rubus), blueberry, and Viburnum populations. Increases occurred in the proportion of red spruce (P. rubens) and yellow birch (Betula alleghaniensis) in the forest canopy. The spruce-fir moss spider, Microhexura montivaga, and a narrowly endemic lichen, Gymnoderma lineare, that inhabit this unique habitat have now been listed as a federally endangered species. Changes in avian species and populations also have been observed in other studies (Rabenold et al., 1998).

Control of the adelgids with insecticides has not been successful or practical, particularly in Fraser fir populations residing in the Great Smoky Mountains National Park. Biological controls have been attempted (Schooley et al., 1984; Humble, 1994), but none has demonstrated satisfactory levels of success to date. It is hoped that biological controls that are being studied for the hemlock woolly adelgid also will be successful with the balsam woolly adelgid. A planting of genotypes from different mountaintops was established in the Great Smoky Mountains National Park during the early 1990s to conserve the genetic resources of this fir species (S.E. Schlarbaum, personal communication, September 2002).

Sources
Alsop, F. J., III, and T. F. Laughlin. 1991. Changes in the spruce-fir avifauna of Mt. Guyot, Tennessee, 1967-1985. J. Tenn. Acad. Sci. 66: 207-209.

Annand, P. N. 1928. A contribution toward a monograph of the Adelginae (Phylloxeridae) of North America. Stanford Univ. Press, Palo Alto, Calif. 146 pages.

Balch, R. E., J. Clark and J. M. Bonga. 1964. Hormonal action in production of tumors and compression wood by an aphid. Nature 202: 721-722.

Hay, R. L. 1978. Fraser fir in the Great Smoky Mountains National Park: Its demise by the balsam woolly aphid (Adelges piceae Artz.). Department of Forestry, Wildlife, and Fisheries, The University of Tennessee, Knoxville. 125 pages.

Humble, L. M. 1994. Recovery of additional exotic predators of balsam woolly adelgid, Adelges piceae (Ratzeburg) (Homoptera: Adelgidae), in British Columbia. Can. Entomol. 126: 1101-1103.

Johnson, K. D. 1980. Fraser fir and woolly balsam adelgid: a summary of information. Southern Appalachian Research/Resource Management Cooperative, Western Carolina University, Cullowhee, North Carolina. 62 pages.

Kotinsky, J. 1916. The European fir trunk louse, Chermes (Dreyjusia) piceae (Ratz.). Ent. Proc. Soc. Washington 18: 14-16.

Mitchell, R. G. and P. E. Buffam. 2001. Patterns of long-term balsam woolly adelgid infestations and effects in Oregon and Washington. West. J. Appl. For. 16: 121-126.

Rabenold, K. N., P. T. Fauth, B. W. Goodner, J. A. Sadowski, and P. G. Parker. 1998. Response of avian communities to disturbance by an exotic insect in spruce-fir forests of the southern Appalachians. Conservat. Biol. 12: 177-189.

Schlarbaum, S. E. Department of Forestry, Wildlife, and Fisheries, University of Tennessee, Knoxville, TN. September 2002.

Schooley, H. O., Harris, J. W. E., and Pendrel, B. 1984. Adelges piceae (Ratz.), Balsam Woolly Adelgid (Homoptera: Adelgidae). In J. S. Kelleher and M. A. Hulme (eds.). Biological Control Programmes against Insects and Weeds in Canada 1969-1980, Commonwealth Agricultural Bureaux, England, 1984.

Smith, G. F., and N. S. Nicholas. 2000. Size- and age-class distributions of Fraser fir following balsam woolly adelgid infestation. Can. J. For. Res. 30: 948-957.