Hemlock Woolly Adelgid
Adelges tsugae

The hemlock woolly adelgid, is a fluid-feeding insect that feeds on hemlock trees throughout eastern North America, including Pennsylvania. The egg sacs of these insects look like the tips of cotton swabs clinging to the undersides of hemlock branches.

Identification:

These small insects display several different forms during their life history, including winged and wingless forms. Generally, they are brownish-reddish in color, oval in shape, and about 0.8 mm in length. Crawler stage nymphs produce white cottony/waxy tufts which cover their bodies and remain in place throughout their lifetime. The white masses are 3 mm or more in diameter. The presence of these masses on the bark, foliage, and twigs of hemlock is a sure sign of hemlock woolly adelgid.

Injury:

Immature nymphs and adults damage trees by sucking sap from the twigs. The tree loses vigor and prematurely drops needles, to the point of defoliation, which may lead to death. If left uncontrolled, the adelgid can kill a tree in a single year. When not at serious risk to the tree, presence of the dirty white globular masses of woolly puffs attached to the twigs or base of needles reduces the value of ornamentals.

Biology and History:

There are four forms of this insect. Each form goes through six life stages (egg, four nymphal instars, and adult). As a cool weather species, most development of these stages occurs between October and June. As temperature rises thereafter, the first instar nymphs go into a dormant stage. Eggs are laid by adult adelgids the following February or March. Half of these eggs develop into a winged, migratory, asexual form that migrate to spruce. The other eggs develop into wingless adults that remain on the hemlock tree.