The balsam woolly adelgid (''Adelges piceae'') is small wingless

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

that infests and kills

fir Firs are evergreen coniferous trees belonging to the genus ''Abies'' () in the family Pinaceae. There are approximately 48–65 extant species, found on mountains throughout much of North and Central America, Eurasia, and North Africa. The genu ...

s. In their native Europe they are a minor parasite on

silver fir Silver fir is a common name for several trees and may refer to: *''Abies alba'', native to Europe *''Abies amabilis'', native to western North America *''Abies pindrow ''Abies pindrow'', the pindrow fir, West Himalayan fir, or silver fir, is ...

and Sicilian fir, but they have become a threat especially to

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''), sometimes spelled Frasier fir, is an endangered species of fir native to the Appalachian Mountains of the southeastern United States. They are endemic to only seven montane regions in the Appalachian Mountains ...

after they were introduced to the United States around the beginning of the 20th century. Because this species is not native to North America, 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 A ...

s within the bark of trees larger than about four centimeters in diameter at breast height. As it feeds, it releases toxins contained within its saliva. These toxins reduce the conductance of

sapwood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin that ...

being built, which causes water stress and kills the trees.

Impact

The

Great Smoky Mountains National Park Great Smoky Mountains National Park is a List of national parks of the United States, national park of the United States in the southeastern United States, southeast, with parts in North Carolina and Tennessee. The park straddles the ridgeline o ...

, straddling

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

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. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

in the

Southeastern United States The Southeastern United States, also known as the American Southeast or simply the Southeast, is a geographical List of regions in the United States, region of the United States located in the eastern portion of the Southern United States and t ...

, contains about 75% of all southern spruce-fir ecosystems. These ecosystems covered vast portions of the Southeast during the Last Glacial Period, when the climate was cool and moist. Since the retreat of the

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

s, this ecosystem has been confined to the higher elevations in the mountains of the Southeast. The spruce-fir forest has evolved as an

ecological island An ecological island is a term used in New Zealand, and increasingly in Australia, to refer to an area of land (not necessarily an actual island) isolated by natural or artificial means from the surrounding land, where a natural micro-habitat exists ...

, away from any other ecosystems of its type. This has presented valuable research and a unique habitat. These forests have a very dense

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

and a moist

understory In forestry and ecology, understory (American English), or understorey (English in the Commonwealth of Nations, Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the Canopy (biology), forest ca ...

. 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 of ...

species.

Red spruce ''Picea rubens'', commonly known as red spruce, is a species of spruce native to eastern North America, ranging from eastern Quebec and Nova Scotia, west to the Adirondack Mountains and south through New England along the Appalachians to wester ...

, the spruce component of the spruce fir ecosystem, has also been suffering declines.The spruce-fir moss spider, which lives on moss mats below the forest canopy, is considered endangered because of the decline of the Fraser fir. Although the fir population in the Great Smoky Mountains National Park was decimated by woolly adelgids in the 1960s through 1980s, there has been some recovery since then. The number of adult firs has increased over 30 years, with

Kuwohi Kuwohi (, also known as Clingmans Dome, its former official name) is a mountain in the Great Smoky Mountains of Tennessee and North Carolina in the Southeastern United States. At an topographical summit, elevation of , it is the highest mountai ...

having three times as many adult trees as of 2020 as in the 1980s. The balsam woolly adelgid also has a significant impact on

Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...

forests. Specifically,

grand fir ''Abies grandis'' (grand fir, giant fir, lowland white fir, great silver fir, western white fir, Vancouver fir, or Oregon fir) is a fir native to northwestern North America, occurring at altitudes of sea level to . It is a major constituent of t ...

and

subalpine fir ''Abies lasiocarpa'', the subalpine fir or Rocky Mountain fir, is a western North American fir tree. Description ''Abies lasiocarpa'' is a medium-sized evergreen conifer with a very narrow conic crown, growing to tall, exceptionally , with a t ...

Washington Washington most commonly refers to: * George Washington (1732–1799), the first president of the United States * Washington (state), a state in the Pacific Northwest of the United States * Washington, D.C., the capital of the United States ** A ...

and

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

can serve as hosts. Extensive mortality by 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

{{Authority control 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