Keep an eye out for Hemlock Woolly Adelgid: An Invasive Forest Pest!

Hemlock Wooly Adelgid (HWA) is an aphid like pest that attacks and kills Eastern Hemlock (Tsuga canadensis) trees. This small invasive insect is native to Eastern Asia and was first observed in Southwestern NS in 2017. HWA is now expanding northward through the province!

Hemlock Woolly Adelgid feeds at the base of Hemlock needles and uses its long mouthparts to reach the tree’s nutrient stores. HWA has a complicated life cycle. In North America, there are two generations and three forms (sisterns, progrediens, and sexuparae). The first-generation hatches in late spring and is called sisterns. Sisterns are all wingless females that reproduce asexually and live for about nine months (lives through the summer and overwinters). The second generation emerges in early spring and lives for about 3 months. The second generation is comprised of two different forms, progrediens and sexuparae. Progrediens are all wingless female adults that reproduced asexually. Sexuparae are winged adults that consist of females and males. Sexuparae adults are not an important stage of the HWA lifecycle in North America. Due to the absence of the secondary host spruce species (Picea torano), these winged adults die before they can reproduce. Therefore, in North America HWA reproduces exclusively asexually. Each generation can produce over 150 eggs. Once this species has become established in a habitat, its population grows rapidly.

How to identify:
A key identifying feature is the presence of small "woolly" sacs at the base of hemlock needles on the underside of young twigs. HWA most noticeable in early spring/late winter when the white balls of “wool” are the largest. Some infestations may occur at the tops of hemlock trees and are not visible on the lower branches. Therefore, it is important to check fallen branches under hemlocks trees for infestation.
Sisterns adults are 1.4 mm long, progrediens adults are 0.9 mm long, and sexuparae adults are 1.1 mm long. Sisterns and progrediens adults are black, wingless, have heavy wax coats, and lay clusters of oblong amber eggs (0.3–0.4 mm long) in white woolly ovisacs. Newly hatched HWA are called first nymphal instars (also called crawlers), and this is the mobile stage. During this stage, they are less than 0.44 mm long and brownish orange in colour.

Eastern hemlock trees infested with HWA will exhibit premature dieback, needle loss, foliage thinning, and tree death in 4-15 years. Hemlock crowns which are normally a shiny dark green colour will appear thinner and greyish green in colour when infested.

Eastern Hemlock is a foundational tree in Nova Scotian forests, especially on riverbanks and lakeshores. Wide-scale Hemlock death causes changes in forest nutrient cycling, and deprives birds, moose, and deer of winter shelter and food. If adjacent to water, Hemlock death increases erosion rates, and decreases the shade available to aquatic organisms.

HWA is unable to successfully spread from area to area due to the absence of an effective winged adult stage. Therefore, relies on other means to disperse such as wind, animals, and humans.

What can you do?
Help reduce the spread of HWA by following Play Clean Go and Buy Local Burn Local. When going for a hike or other outdoor adventures make sure to clean your gear, clothing, and pets before and after to avoid unintentionally spreading HWA. These are small insects that can easily go undetected. It is advised to use a lint roller, when possible, to reduce the chance of spread. In addition, when going camping buy your wood locally instead of bringing it with you to reduce the spread of HWA. Make sure to not bring this wood back home with you as well.

Early detection of HWA is critical to protecting Nova Scotia’s forests and environment. Be vigilant, keep an eye out for small "woolly" sacs at the base of Hemlock tree needles! These could be HWA egg sacks. In addition to reporting sighting on iNaturalist it is important to report sightings to CFIA at the following link: You can also report sighting to NSISC at our website:

Limbu, S., Keena, M. A., & Whitmore, M. C. (2018). Hemlock woolly adelgid (Hemiptera: Adelgidae): a non-native pest of hemlocks in eastern North America. Journal of Integrated Pest Management, 9(1), 27.
Canadian Food Inspection Agency (2021). Adelges tsugae (Hemlock Woolly Adelgid) - Fact Sheet.

Publicado el marzo 31, 2023 08:27 TARDE por hgrimshaws hgrimshaws


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