Researchers are looking to western hemlock trees on the Miller Peninsula to collect data that could help save hemlock trees on the East Coast from dying at alarming rates.

Elizabeth Sussky, Ryan Crandall and Joseph Elkinton are all part of a biological control experiment funded by the U.S. Forest Service importing natural enemies of an invasive insect from the area that feeds and predates on hemlock trees.

Hemlock trees on the East and West Coast are predated on by small insects called hemlock woolly adelgid. This invasive insect originates from Asia and lives and feeds on hemlock trees with the ability to reproduce 100 fold per insect every time females lay eggs. Left unchecked, these insects could drive hemlocks to extinction on the East Coast.

“We’re talking about an insect that’s killing trees by the millions across the forests of the eastern United States,” Elkinton said.

Elkinton is a professor for the Department of Environmental Conservation at the University of Massachusetts – Amherst and has been conducting similar experiments at the Seattle Arboretum for the past three years.

According to Elkinton, eastern hemlock trees with heavy infestations of the invasive insect are dying all across the East Coast. Eastern hemlock have been dying over the span of 20 years while western hemlock found with infestations of the same species of insect — particularly on the Miller Peninsula — are thriving.

The team is collecting 680 samples of western hemlock with heavy infestations of the invasive insect found on the Miller Peninsula so they can bring them to the Seattle Arboretum where they will conduct experiments and collect data.

Elkinton explained the idea of the experiment is to try to find data that answers the question, “What is it that’s regulating the densities of the adelgid?” particularly in the western hemlock.

Sussky is a University of Massachusetts – Amherst graduate whom Elkinton said pioneered this experiment in his lab for her master’s thesis. She will work part-time for the U.S. Forest Service and lives on the Miller Peninsula where she has been collecting samples of western hemlock.

“It’s so much fun to reconnect with this and it’s a great time because my job is seasonal, I have a lot of gratitude for being in his lab four years ago,” Sussky said.

Crandall is a graduate student at the University of Massachusetts – Amherst who also will use this experiment for his master’s thesis. He also has been working under Elkinton as a research technician.

“It’s a big undertaking, most people like us would be unwilling to do this kind of thing, because it’s too difficult,” Elkinton said.

Theories

The team believes one possibility of the thriving western hemlock could be due to a natural predator that solely feeds on the invasive insect, a specialized beetle called Laricobius nigrinus native to the Pacific Northwest.

“The Forest Service is already spending millions of dollars to import these beetles, but without ever doing this kind of research there’s no “does the beetle actually regulate these densities?’” Elkinton explained.

This predator is a specialized beetle that only predates on the hemlock woolly adelgid, acting as a biological control agent for the hemlock. These beetles could be contributing to the success of western hemlock.

“The beetle is specialized on the adelgid, it’s not going to become very common,” Elkinton assured. “If it succeeds in knocking down the adelgid, it itself will decline to a lower density.”

Elkinton explained pesticides cannot be used on the invasive insects killing the hemlocks because it would be too expensive.

“We are convinced these predators are regulating the densities of the adelgid out here, our data suggests that,” Elkinton said.

“It is the only thing that could save the hemlocks in the eastern United States, there’s nothing else that can do it.”

The experiment

After the team collects enough samples of infested western hemlock, they will take the samples to the Seattle Arboretum where they will inoculate 20 eastern and western hemlock trees when the invasive insect eggs are ready to hatch. They will tie mesh bags around some of the eastern and western hemlock branches — excluding predators — and put them side by side with branches that are not covered with the mesh bags and can compare the results.

Before the team inoculates the hemlock trees, they will count how many insects they put on each tree, estimating it will be in the tens of thousands. When the hemlock woolly adelgid eggs hatch, they are estimating there will be about 5 million crawlers to infest the trees.

“That’s what we hope to answer and will help the Forest Service decide which of these natural enemies they want to focus on in terms of introducing them to the East Coast,” Elkinton said.

The team will then collect data and follow the populations over time.

Hemlock trees are a keystone species, Sussky explained, meaning its abundance has a big impact on other species in an environment.

“The hemlock is an important tree ecologically in the eastern U.S.,” Elkinton said.

He explained that hemlock trees grow along stream valleys and are a good provider of shade. When hemlock trees die, they are replaced with other trees that do not provide the same amount of shade and the result is stream temperatures go up, trout leave the stream and various things happen to the stream ecology.

“I never thought I would see this happen when I moved to Massachusetts back in 1980, none of these species were present,” Elkinton said of the invasive insects. “It could drive the hemlock to extinction.”

Hope

Crandall said he has personally seen the effects of these insects on hemlock trees in his backyard in Massachusetts.

“I had a line of hemlock trees in my backyard growing up and they’ve been hit pretty hard,” Crandall said. “We cut a few down this year for the first time which is really sad, I hate to lose those.”

He is hoping this experiment can help stop more hemlock trees from dying. “If we could find something that could help the eastern hemlock here that could be amazing,” he said.

“One of the things I love about the work we do is most ecologists study problems and we fix problems,” Elkinton said.

The team will continue its research throughout the next couple of weeks, collect data and determine the next steps for the experiment. Elkinton said they could have good answers in the next year.