Joining forces against hemlock woolly adelgid

June 2022 | Canadian Food Inspection Agency | by Nicole Mielewczyk and Erin Appleton, Plant Health Surveillance Unit

Many would have been discouraged by the pouring rain and cold winds that settled in southern Ontario on April 21, 2022. But a dedicated team of specialists was undeterred and eager to get to work on some important research on hemlock woolly adelgid (HWA) - an aphid-like insect pest that attacks and kills hemlock trees.

The team consisted of a plant health survey biologist and student intern from the Canadian Food Inspection Agency (CFIA), as well as biologists and technicians from Natural Resource Canada’s Canadian Forest Service (CFS), and the Biodiversity Institute of Ontario (BIO) at the University of Guelph. The group assembled at the site of the HWA infestation in Wainfleet, Ontario, in the Niagara region. They were there to set up a number of trials to evaluate passive methods for detecting HWA. The pest was first detected in Wainfleet by CFIA plant health inspectors in 2019. In Ontario, HWA has also recently been detected in the nearby Town of Fort Erie and the City of Niagara Falls. Across Canada, HWA has also been detected in southwestern Nova Scotia, as well as in British Columbia.

The threat of HWA

HWA egg sacs look like cotton balls or clumps of snow, and are found on a tree’s twigs, near the base of a needle. It can spread by many pathways and has been known to wipe out whole forests of hemlock trees. The CFIA works with partners in plant health protection, like CFS and BIO, to better understand and reduce the impacts of this harmful pest. To slow the spread of HWA and protect non-infested areas in Canada, the CFIA monitors the pest and restricts the movement of plants and plant parts containing bark or foliage from hemlock and susceptible wood products, including firewood, from infested areas. Citizen scientists also have a role to play - if you spot HWA outside of British Columbia, report it to the CFIA.

Working together for better biosurveillance

The team that assembled on that cold April morning was part of a collaborative initiative that blossomed from the CFIA’s Federal Assistance Program and was established to support BIO in growing Canada's capacity for using molecular tools in plant pest biosurveillance. The initiative has led to many projects to help detect and respond to plant pests and build DNA reference libraries that add to what we know about pests.

As part of this initiative, 12-unit Lindgren Funnel traps (see photo, below) were set up roughly 600 to 900 metres around the known infested site, with one in each cardinal direction. The fluid in the traps will be collected monthly and sent to BIO for environmental DNA (eDNA) analysis. Samples will be screened for DNA of HWA and other regulated plant pests that may be otherwise challenging to detect.

Sharing tools and knowledge

While on site, each organization had the opportunity to explain their methods, offer assistance and provide updates on various projects. For example, BIO demonstrated how to use their in-field eDNA sampler on HWA-infested branch wash water and bog water. Bog water samples are analyzed to determine if the DNA of HWA and its predators (which can act as biocontrol agents) can be effectively isolated from wastewater at infested sites, while the wash water is used as a control. This provides important clues for the monitoring and management of HWA.

CFS also explained their ongoing trials for insecticide evaluation and for improving survey and detection methods. A second collaborative site visit was planned to include a demonstration of the CFS project.

The power of collaboration

This interagency initiative has advanced the study of an important plant pest by using new technologies and approaches. In addition, it provided an excellent opportunity for team building, knowledge transfer and networking. The CFIA student intern learned first-hand about the various roles and opportunities within all of the organizations, and was able to see the scientific value of collaboration. Tales of previous experiments and field days with terrible weather were shared and future collaborative initiatives were discussed. For example, it was exciting to learn that CFS is exploring another type of trap for HWA detection designed for community scientists. This type of informal information exchange often leads to the most creative and innovative ideas. For everyone involved, it was an important reminder of the shared enthusiasm and expertise that this collaborative initiative provides to advance plant health protection.

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