Community Notebook

Battle for the Hemlocks:
Adelgid vs. Beetle

There is a creeping menace on the eastern seaboard and it’s not the sighting of Al Qaeda submarines off Martha’s Vineyard. It’s the hemlock wooly adelgid, and people are scared.

“I’ve talked to a lot of desperate people out there who want to save their trees,” Jason Denham, Senior Forester with the Department of Environmental Conservation’s Division of Lands of Forest’s Albany office told me in late February. “We get calls fairly frequently; either [people] have something wrong with their trees and they don’t know what it is, or they’ve heard of the hemlock wooly adelgid and they have it on their trees and they want to know what they can do. Private landowners, non-governmental organizations, historical societies that have property, state parks—a lot of different people and a lot of different entities are obviously, with good reason, very concerned about their hemlock resource.”

What’s so frightening about an aphid-like insect only two millimeters long? It’s killing the Eastern (also known as Canadian) hemlocks in its path, from North Carolina to Maine. Some scientists believe without an aggressive approach to protect the hemlock—“a very hearty tree, they’re not fussy, they’re shade tolerant and they’ll grow in just about any type of soil,” according to Michael Kudish, professor of Forestry at Paul Smith College and author of The Catskill Forest—that the hemlock might suffer massive die-offs. According to Brad Roller, manager of the display gardens at the Institute for Ecosystem Studies in Millbrook and part of ad hoc adelgid group at the Institute, “The Forest Service and the USDA are literally writing off the southern ranges of the Canadian hemlocks just because it’s too late, they’re not going to recover.”

The hemlock wooly adelgid, an Asian native, was discovered in the US in 1924. With no natural predators here, the adelgid has been feasting and multiplying ever since.

The adelgid itself is not visible to the naked eye, but the white woolly secretion that protects the adelgid and its eggs is visible and indicates infestation. Adelgids feed on hemlocks from the base of the needles, causing the needles to dry up and drop from the tree within a few months. Once a tree becomes heavily infested, major limbs usually die within two years, and tress often die within four years. Because individual adelgids are so small, the first indication of infestation is usually the discovery of the white, cottony egg sacs. In addition to protecting the eggs, the fibrous sacs help transport adelgids by sticking to bird feathers or mammal fur. Wind also carries the sacs between trees, spreading infestations further.
While the spraying of insecticidal soaps and horticultural oils provides effective control of ornamental hemlocks, this form of pest abatement is virtually impossible in the forest, as each branch must be thoroughly coated manually. (The scientists I spoke to referred to the US adelgid population in the unknown billions.) Therefore, researchers have looked for natural predators of the adelgid in Japan and China in an attempt to find a biologic control.

Enter Dr. Mark McClure, chief scientist of the Connecticut Agricultural Research Station. Dr. McClure may have found just the pest he was looking for in Japan in 1992, when he discovered the previously unknown beetle Pseudoscymnus tsugae. The most common and effective insect predator in Japan, according to Dr. McClure, P. tsugae has evolved as a specialized predatory-prey system in Japan and is the most promising biological control candidate for the adelgid. “It’s one of the most effective natural enemies that’s available,” said Dr. McClure, adding that P. tsugae “possesses many of the qualities of a good biological control agent.”

Preliminary laboratory and field testing of McClure’s beetle seems to bear out his assessment of its promise. P. tsugae is extremely host specific, meaning that, given a choice, it prefers to eat adelgids more than anything else; they are non-native, so they are not in direct competition with native species for food or habitat (no native species were eating the adelgids anyway); and according to the DEC’s Denham, scientists are reasonably confident that it will, at the very least, do no harm.

Since 1997, 650,000 beetles have been released at 100 sites on the East Coast with adelgid infestations. (The beetle releases are part of an experimental program run by the USDA and the US Forest Service, and all the scientists were at pains to state that P. tsugae is not available to the public.) Denham, who is the interim head of New York’s beetle release program, explained that the beetles are reared in a New Jersey “beneficial insect” lab, and then distributed evenly among the 10 states in the release program. (Connecticut rears and releases its own beetles.) The beetles come in a bucket, what Denham referred to as something akin to a Kentucky Fried Chicken bucket, and are brought to an infested tree, and then freed to feast on the adelgid.

In New York, where the adelgid has not yet penetrated the northern portion of the state, 20,000 beetles have been released since 1997 in the Hudson Valley, at seven sites in Putnam, Greene, Columbia, and Ulster counties. While the DEC is still in the process of scouting sites, Denham is planning two more releases of P. tsugae this spring in the Hudson Valley.

But what of biological controls gone awry? What happens when a species is introduced to a non-native environment and there are unforeseen consequences, as in the well-known case of bufo marinus? The bufo, also known as the cane toad, was intentionally introduced into Australia in the 1930s to combat the cane beetle. The toad proceeded to eat the beetles and then multiply in great numbers, plaguing Australia ever since, to the point that it has muscled many native species out of their natural habitats and is now itself being considered for biological control.

While Brad Roller of IES is quick to praise Dr. McClure and his methodology evaluating P. tsugae as a suitable biological control, Roller is less sanguine about the consequences of introducing a non-native species into the environment. “Even though the science was good at seeing how host-specific these beetles are, the long-term ramifications of biological controls…” Roller paused, “there’s nightmares to be told out there. And let’s just hope, years from now, this doesn’t become a problem.”

Scientists are guardedly optimistic about the fate of the hemlock, and the Hudson Valley’s trees are better off than in most areas. “For our area the prognosis is relatively good,” Roller said, “we have a healthier stand.” But for now, the Eastern hemlock’s best chance is a Japanese bug that comes in something strikingly similar to a KFC bucket.

—Brian K. Mahoney