Dealing with the Adelgids: Nova Scotia HWA Working Group Calls in Expert on Invasive Insect

As the Hemlock Woolly Adelgid threatens the integrity of Maritime forests, government departments, research organizations and stakeholders alike are preparing their defence. And in their search for expertise in combating this invasive insect, they’ve looked no farther than New York State.

Dr Mark Whitmore, a forest entomologist with Cornell University, has been studying the Hemlock Woolly Adelgid (HWA) forty years now, throughout its conquest of the eastern United States. With its infestation of Nova Scotia’s five southern counties confirmed this summer, he visited the province’s newly formed HWA Working Group the week of December 11 to share his experience, and to help formulate a local response.

When asked how many hemlocks have already fallen to HWA in the United States, he replied, “I have no idea, but countless trees…billions. You just need to look throughout Pennsylvania and south to Georgia; the devastation is mind-boggling.”

HWA is a millimetre sized insect native to Asia where it depends wholly on hemlocks to sustain itself, as well as in the Pacific northwest where it’s adapted to North America’s Western hemlock. In both regions these adelgids are held in check by predatory insects, while on the eastern seaboard its devastation goes entirely unchallenged by native predators. There offspring are so small as to be carried off by the wind, spreading like dandelions across ecosystems unprepared for their insatiable appetites.

The Trees

“Ecologically, [the Eastern hemlock is] what we call a foundation species,” said Dr Whitmore, “basically responsible for forming the habitat on which myriad other species depend.”

In much of the eastern United States where hemlock is the most common conifer, and in Nova Scotia where it’s invariably the oldest, Dr Whitmore said they’re especially important to wildlife. Rivers and watersheds dominated by hemlocks, for example, are shaded from the sun year-round by their evergreen foliage, ensuring aquatic temperatures cool enough for the spawning of Brook trout. And during winter, this tree intercepts enough snowfall to maintain shallow walkways in its understory, an important service for species such as deer.

“Foundation species are generally so common that they’re taken for granted,” he said. “If you take them out of the system, the system collapses.”

The Controls

Dr Whitmore described the thoughtful application of insecticides as an affordable and benign measure against HWA. Hemlocks treated with his preferred remedy are safe from the pest 5-7 years, but there are of course too many trees and too many adelgids for this to be a long-term fix.

Instead, he and his colleagues have used insecticides to preserve outstanding hemlock forests and to temper the spread of this insect wherever possible, giving them time to implement a more permanent solution.

“Our whole strategy is to use insecticides to preserve valuable hemlock resources across the landscape, be them scenic, genetic or ecological. The long term plan, in my mind, is the implementation of biological controls, which could take years.”

The reason HWA co-exists sustainably with the Western hemlocks of BC is because of the aforementioned predators specialized to eating adelgids. With extensive lab work, Dr Whitmore and his colleagues have demonstrated that two of these predators – a beetle and fly – would rather starve than change their diet.

“They only eat adelgids,” he said with scientific certainty, “and as far as I’m concerned, that’s a good thing.”

With no demonstrated harm to the ecosystems of the eastern seaboard, these two predators have been introduced so they might devour HWA, creating what’s called a biological control. They are the beetle known as Little Larry (Laricobius nigrinus) and a species of Silver fly (Leucopis argenticollis), both slowly establishing themselves in selected states.

Once these predators have achieved a population size sufficient to control HWA, it’s Dr Whitmore’s expectation the ecosystems in question will find balance. Because this will take time, however, every year counts, especially in the early stages of an infestation such as in Nova Scotia.

Unfortunately there are no insecticides registered and available for use against HWA in Canada, and while Little Larry and the Silver fly are native to BC, neither have yet been brought to Nova Scotia. It’s Dr Whitmore’s opinion that these obstacles should be overcome quickly, and that the Maritimes should follow the example of eastern states.

“Assume the worst and hope that you’re wrong,” he said. “I’m working on the assumption that all Eastern hemlocks will disappear, because I don’t want them to. I’m going to fight as hard as I can to keep them on the landscape. If it were me, that’s what I’d do here, because I’ve seen important stands deteriorate while waiting for biological controls.”

Hit the Ground Running

The Nova Scotia HWA Working Group consists of the Canadian Food Inspection Agency, Canadian Forest Service, Parks Canada, Mersey Tobeatic Research Institute, Nova Scotia’s Department of Natural Resources and researchers from various universities.

In the evening of Tuesday, December 12, working group members sat down with Nova Scotian woodlot owners to field their questions concerning HWA. During this meeting, government representatives said there was talk of testing registered Canadian pesticides for their effectiveness against HWA, as well as other studies aimed at introducing the aforementioned biological controls to Nova Scotia.

“The working group is discussing biological pest control seriously,” said Ron Neville of the Canadian Food Inspection Agency. “It may be what we need to have happen here.”

Zack Metcalfe is a freelance journalist, author, and writer active across the Maritimes. This article was originally published with Rural Delivery Magazine.

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