Hemlock Woolly Adelgid in Nova Scotia
Hemlock Woolly Adelgid (HWA)
The hemlock woolly adelgid (adelges tsugae) is an insect that feeds on the sap of its host, leading to a high rate of tree mortality where its population is not native and held in check by predators and species resistance.
For an up-to-date distribution map for Nova Scotia, see CFIA (2024), and for the eastern seaboard, see the USDA Forest Service (2022).
Lifecycle
The lifecycle of the HWA is unusual among insects in Nova Scotia in that it is active in the winter months and dormant in the growing season. Each year there are two generations of HWA. (1) The sistens, “settling”, generation hatches in late spring/early summer. Its nymphs quickly move to the base of hemlock needles, attach, and are dormant for the summer. They feed throughout the fall and winter, gradually developing their characteristic protective “woolly” covering. These white sacs are most visible in the late winter and early spring. By this time, a single insect can lay ~50-175 eggs. The (2) second progrediens, “advancing”, generation hatches from these in the early spring. They begin feeding immediately, and quickly reach maturity. By the late spring, eggs (~25-125 eggs per female) for the next sistens generation have been laid and begin to hatch. This two-generation lifecycle leads to very rapid population growth.
Appearance
Individual insects are tiny, growing at most to 1.5mm in length as an adult. Their presence is usually detected in the early spring, after the first generation of HWA has grown its waxy white covering over the winter.
For further information, see Inspection Canada.
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