Hemlock Wooly Adelgid - Tsuga canadensis

ID: 

The hemlock woolly adelgid (HWA) is a small insect that threatens the health and survival of eastern hemlock trees (mainly Tsuga canadensis). These are very small insects that develop a distinctive shelter of white wool-like hairs as they mature, making them look like very small cotton balls attached to the undersides of hemlock needles. They have piercing sucking mouthparts that are used to consume starch and sugars from the vascular system. There are two generations per year. Sistens are the overwinter generation, which lasts from mid summer to early spring. The Progredien generation lasts from April to June. These insects are asexual, but can produce sexually productive, winged females in the Progredien generation. These winged adults die, as they require a specific japanese spruce to start maturation, in North American populations. 

Signs and Symptoms: 

Insects feed on the starch in the sap of trees, robbing the tree of energy. Their feeding causes needles to dry up, turn a grayish color, and fall off. In addition, because they kill the apical buds, HWA prevents the tree from producing new growth. Because infestations are so severe, HWA can kill a tree within 4 to 10 years.  In addition, infestation can weaken trees making them highly susceptible to other problems.

Spread and Impacts: 

Native to Asia, HWA had been spotted in Kentucky in 2006, and has spread to new counties in the eastern part of the state. They have been in the United States since 1951 in Richmond, Virginia and infest both eastern hemlock and Carolina hemlock. In some areas with infestation, HWA can take out over 80% of the trees. Infested hemlocks can be dangerous, as HWA sucks vital nutrients from the tree causing it to become brittle. 

Control: 

There are both chemical and biological control methods practiced to control HWA in infested areas. Use of pesticide has been found to be effective on this insect by soap and soil injections. As well, biological control through the introduction of a Pacific Northwestern Species of Laricobius beetle that is specialized to be a threat to reduce numbers as they eat the ovisacs on the hemlocks.