Identifying the Hemlock Woolly Adelgid
Adelgids are a small family of insects closely related to aphids that feed on the plant sap of conifer trees and, in the hemlock woolly adelgid’s case, hemlock and spruce trees. The insect measures less than 1/16 inch (1.5mm) and is covered in a wool-like wax filament, giving the pest a “cottony” appearance. Females are black, oval, soft-bodied, and about 1.5 mm long. HWA is primarily found on the underside of hemlocks’ branches, nestled against the base of the needles.
The Life Cycle of the HWA
The hemlock woolly adelgid possesses an intricate two-year life cycle, encompassing four immature stages and culminating in a reproductive adult phase. Throughout late winter and early spring, as temperatures climb, adult female HWAs begin laying eggs. These clusters of eggs, housed within white filamentous wax masses, continue to be laid until June. Measuring 0.25 mm in length and 0.15 mm in width, the oblong eggs have a brownish-orange color. Depending on the warmth of the spring season, hatching starts in early April and typically concludes by the end of June.
Emerging as reddish-brown nymphs, or “crawlers,” these young insects display a delicate white fringe near their anterior. Once settled, crawlers grow to approximately 0.3 mm long, and take on a black hue with a white fringe that encircles their bodies and extends along their dorsal side. As these nymphs develop, their color deepens to a dark reddish-brown, and their size progressively increases due to active feeding habits. By late September, these mature female insects reside on trees, overwintering before repeating the reproductive process of the species.
Recognizing an Infestation
The most apparent sign of HWA infestation is the white, “cottony” egg sacs on the underside of hemlock branches that the females produce when laying eggs. These egg sacs look much like the tip of a cotton swab and typically persist even after the insects are dead. Other signs include needle loss, reduced twig growth, and dieback of branches.
Damage Caused by Hemlock Woolly Adelgid
The impact of an HWA infestation on eastern hemlock trees can be catastrophic to the tree, depending on the extent of the infestation. The adelgids use sharp, syringe-like mouthparts, or stylets, to siphon off essential plant fluids from host plants. This feeding activity takes a toll on the plant’s overall health.
A moderate population of the hemlock woolly adelgid may lead to a noticeable decline in the health and vigor of your trees. However, the consequences become more serious in a severe infestation. This could result in a premature shedding of needles, diminished growth of twigs, significant dieback, and in worst cases, the loss of the tree. This danger to the trees makes early detection and decisive action in managing these unwelcome pests important.