Balsam woolly adelgids (''Adelges piceae'') are small wingless

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

s that infest and kill firs, especially

balsam fir ''Abies balsamea'' or balsam fir is a North American fir, native to most of eastern and central Canada (Newfoundland west to central Alberta) and the northeastern United States (Minnesota east to Maine, and south in the Appalachian Mountains to ...

and

Fraser fir The Fraser fir (''Abies fraseri'') is a species of fir native to the Appalachian Mountains of the Southeastern United States. ''Abies fraseri'' is closely related to ''Abies balsamea'' (balsam fir), of which it has occasionally been treated a ...

. They are an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...

from

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

introduced to the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

around 1900. Because this species is not native to the United States, the Fraser fir has not evolved any type of defense against it.

Reproduction

These insects typically lay about one hundred eggs and have three generations per year. The adelgid attacks the tree by feeding in

fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure ...

s within the bark of trees larger than about four centimeters in diameter at breast height. As it feeds, it releases

toxin A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849 ...

s contained within its

saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can ...

. These toxins reduce the conductance of sapwood being built, which causes water stress and kills the trees.

Impact

The

Great Smoky Mountains National Park Great Smoky Mountains National Park is an American national park in the southeastern United States, with parts in North Carolina and Tennessee. The park straddles the ridgeline of the Great Smoky Mountains, part of the Blue Ridge Mountains, w ...

, straddling North Carolina and

Tennessee Tennessee ( , ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. Tennessee is the List of U.S. states and territories by area, 36th-largest by ...

in the

Southeastern United States The Southeastern United States, also referred to as the American Southeast or simply the Southeast, is a geographical List of regions in the United States, region of the United States. It is located broadly on the eastern portion of the south ...

, contains about 75% of all southern spruce-fir ecosystems. These ecosystems covered vast portions of the Southeast during the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

, when the climate was cool and moist. Since the retreat of the

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

s, this ecosystem has been confined to the higher elevations in the mountains of the Southeast. The spruce-fir forest has evolved as an island, away from any other ecosystems of its type. This has presented valuable research and a unique habitat. These forests have a very dense canopy and a moist

understory In forestry and ecology, understory (American English), or understorey (Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the forest canopy without penetrating it to any great extent, but abo ...

. Since the invasion of the balsam woolly adelgid, discovered in 1957, Fraser fir mortality rates have been 90–99%. Although some areas are being regenerated by young firs, there is much change in understory composition, including invasion by both woody and

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...

species. Red Spruce, the spruce component of the spruce fir ecosystem, has also been suffering declines. Some researchers attribute these declines to damage from wind, which is usually blocked by the firs. Balsam woolly adelgids destroyed about 95% of the Fraser firs in the Great Smoky Mountains National Park, creating "ghost forests". The number of adult firs relative to young firs has increased over 30 years, with Clingmans Dome having three times as many adult trees as of 2020 as in the 1980s. One concern is that

acid rain Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists between 6.5 and 8.5, but ac ...

and the deterioration of the

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the l ...

, among other

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...

s, are contributing to a weak immune system for the Fraser firs and making them more susceptible to the balsam woolly adelgids. The

Spruce-fir moss spider The spruce-fir moss spider (''Microhexura montivaga'') is an endangered species of spider found at high elevations in the southern Appalachian Mountains. First identified in 1923, it inhabits moss that grows on rocks underneath the forest canopy. ...

, which lives on moss mats below the forest canopy, is considered endangered due to the decline of the Fraser fir. The Balsam woolly adelgid also has a significant impact on Pacific Northwest forests. Specifically, grand fir,

silver fir Silver fir is a common name for several trees and may refer to: *''Abies alba ''Abies alba'', the European silver fir or silver fir, is a fir native to the mountains of Europe, from the Pyrenees north to Normandy, east to the Alps and the Car ...

and subalpine fir in

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

and

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

all can serve as a host. Extensive mortality due to this pest in the Cascade Mountain range was recorded during the 1950s and 1960s. Land area affected by the adelgid in the Pacific Northwest has increased from 83,325 acres (337 km²) in 2004 to 108,128 acres (438 km²) in 2005.United States Forest Service. (2005). Forest Health Conditions Report. Availabl
online
(Accessed September 11, 2006).

References

{{Taxonbar, from=Q1382443 Adelgidae Insect pests of temperate forests Hemiptera of Europe Insects of the United States Insects described in 1844 Taxa named by Julius Theodor Christian Ratzeburg