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Hemlock Woolly Adelgid

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hemiptera
Superfamily: Phylloxeroidea
Family: Adelgidae
Genus: Adelges
Species: A. tsugae

Hemlock Woolly Adelgid    Elongate Hemlock Scale  Circular Scale   Hemlock Borer

The Hemlock Woolly Adelgid along with the Elongate Hemlock Scale, the Hemlock Borer and the Circular Hemlock Scale are causing destruction to hemlock and spruce trees throughout the eastern United States.  Of the hemlock trees found in the Blue Ridge Parkway and the Shenandoah National Park, 80% have died due to the infestation of the Hemlock Woolly Adelgid.  This article will give detailed information about each of these insects that are destroying Eastern Hemlock trees, Carolina Hemlock trees and spruce trees.

Hemlock Woolly Adelgid

Picture of Hemlock Woolly Adelgid   

Hemlock Woolly Adelgid Tree Destruction, Smokey Mountains    

The Hemlock Wooly Adelgid is a fluid feeding insect that feeds on hemlock trees, particularly the Eastern Hemlock and the Carolina Hemlock tree.  They are found throughout eastern North America from north eastern Georgia to south eastern Maine and west to eastern Tennessee.Hemlock Wooly Adelgid picture
Hemlock Wooly Adelgid were introduced into America in 1924 in the northwest and in 1950 in the northeast.
The Eastern hemlock tree is the state tree of Pennsylvania and is known as the "redwood of the east" because it is the largest and most common tree found in the Smoky Mountains.  Carolina Hemlock trees are also found throughout the southern Smoky Mountains.  Both are very susceptible to damage.  Drought and fungi often weakens the hemlock trees and cause them to become more susceptible to the insect damage. 

The adult Hemlock Woolly Adelgid produces two generations per year.  All are females that reproduce asexually.
In the spring, adults lay from 100 to 300 eggs in egg sacs beneath branches.  Crawlers emerge from April to May. They are spread to other hemlock tress by the wind, birds and mammals.  After hatching, crawlers settle at the end of the hemlock needles where they mature into wingless and winged female adults.  The winged species migrate to spruce trees to feed and lay eggs while the wingless species remain on the hemlock trees and lay more eggs. 

The Hemlock Woolly Adelgid sucks fluid from the hemlock needles.  During feeding, they also inject toxins into the tree that causes needle drop and branch die back.  Affected trees have a grayish green appearance as apposed to the natural shiny dark green color. 

Adults are less than 1/16 inches long.  They are dark reddish brown to purplish black.  As it matures, it produces a covering of wool-like wax filament used to cover themselves and the eggs, protecting themselves from drying out and also from predators.

Because of the abundance of dying Hemlock trees, the Smoky Mountain National Park Forestry released predatory beetles into the park in 2002.  Predatory beetles feed exclusively on adelgids.  The results thus far have been found favorable, but it will take several years for the beetles to increase enough to control all of the infestation.Hemlock Woolly Adelgid Tree Damage
On May 22, 2008, the Hemlock Wooly Adelgid was found in Battleboro, Vermont. They are believed to have been traveled by birds, because the outbreaks were located near birdfeeders and bird baths. An alert warning was issued for infected trees in nurseries and in yards.

Elongate Hemlock Scale and Circular Scale

The Elongate Hemlock Scale and the Circular Scale are both native to Japan.  They are currently found in the District of Columbia and in nine other states from Virginia to southern New England and west to Ohio.  These insects attack the lower parts of the Hemlock tree needles by sucking out their fluids.  They feed on fourteen various species of spruce and fir trees, which are all more susceptible than hemlocks.

Adult female Elongate Hemlock Scales are more common than the Circular Scale, but both tend to feed together on the undersides of the needles.  They are identified by their names: one is elongated and the other is circular.
Adults are soft bodied, legless and wingless.  They are enclosed in a cover that is light yellow to brown.  Adult males have light brown bodies, legs and wings and are enclosed in a white cover.
Crawlers hatch from translucent eggs from under the females cover.  Females molt through three stages before becoming adults, while males molt through five stages.  During the first stage, crawlers have lemon color bodies and secrete its cover as it continues to grow.  During the second stage, they are soft bodied and enclosed in an amber colored cover.  Females grow into adults during the third stage, while the male spins a cocoon and pupates before emerging as an adult.  The adults produce two generations per year in southern states and one generation per year in the northeast.  As crawlers they are able to disperse by wind and birds, increasing their ability to establish new infestations.

Damage from the Elongate Hemlock Scale and the Circular Scale cause foliage to turn yellow and drop.
The trees limbs also dieback and infestations usually begin at the base of the tree and move upwards.

Hemlock Borer

The Hemlock Borer develops on trees that are already stressed and weakened by the Hemlock Wooly Adelgid.
The principle host of the Hemlock Borer is the eastern hemlock tree; however they also attack the Carolina Hemlock, a southern Appalachian species of tree, the Eastern White Pine, the Taramak, the Balsam Fir tree, the Red Spruce tree, the White Spruce tree and the Black Spruce tree. 

The adult Hemlock Borer is a flattened black beetle with a metallic sheen.  They have three to four yellowish spots on each wing cover.  The Larva are translucent white and gradually turn black as they pupate.
Eggs are white and oval.  Adults usually live only two weeks. The majority of the damage is done by the larva stage of the Hemlock Borer.  Larvae that emerge from their eggs in June overwinter in pre-pupal chambers in the outer bark of the tree and pupate the following spring.  Those that emerge from their eggs as late as August overwinter on the inner bark, mature during the summer and overwinter again before emerging to pupate in the spring.

Damage caused by the Hemlock Borer is in the form of small holes in the bark showing the emergence of the adult beetles.  Extensive larva galleries can be found underneath the bark of the tree.  During heavy infestations, woodpeckers will chip away at the bark of the tree searching for larva.

Credits:
Our thanks to Lani Powell for pictures, research and writing which made this
Hemlock Woolly Adelgid information page possible.

Pest Control Supplies    General Pest Control Information    Animals and Pests

Elongate Hemlock Scale  Circular Scale   Hemlock Borer  Hemlock Woolly Adelgid