| Hemlock trees in the Great Smoky Mountains are threatened by the non-native hemlock wooly adelgid, an Asian import that sucks sap from the trees' needles. | | Non-Native Beetle
Key in Park's Battle
One non-native pitted against another in effort to save trees.
GREAT SMOKY MOUNTAINS N.P.—Non-native species have traditionally been enemy number one at national parks, often disrupting the natural balance of ecosystems and spreading disease to native species.
But, as the saying goes, desperate times call for desperate measures. Faced with a likely, rapid death of the park's hemlock trees, officials at Great Smoky Mountains National Park are counting on a non-native species—a tiny, black predator beetle—to control another non-native species. |
Resource managers recently released about 10,000 of the beetles at four sites in the park in an attempt to battle infestations of the non-native hemlock woolly adelgid, an Asian import that kills most of the hemlock trees it attacks by sucking sap from the trees' needles, causing defoliation.
Park officials discovered the hemlock woolly adelgid in May and have since found 30 infested strands of hemlock. They expect to find more infestations throughout the park, which made identifying a swift solution imperative. After consulting with other agencies and states that have dealt with the adelgid, the park decided to try the predator beetle, Pseudoscymnus tsugae.
Years of study went into that decision. The sites at which the beetle was released were chosen because enough adelgids were present to allow the beetle to find its prey quickly and feed swiftly.
One upside of using the beetle is that it is a selective predator. "Research shows this species only preys on adelgids," said park spokeswoman Nancy Gray.
The predator beetles are related to the common native ladybug beetles but are about one-tenth their size.
"No one is likely to see them since they are about the size of a pin head," said park forester Kris Johnson.
The park also tried spraying trees with soap and using injected insecticides, but those methods are not possible in remote forest, said Johnson.
At press time, the hemlock woolly adelgid was beginning its summer dormancy, so it was difficult to tell whether the beetles were effective, Johnson said.
"The [adelgids] are hard to see right now. Once they start to feed again in the fall, we'll have a sense of how much reduction there was," she said. "Next spring, when the hemlock begins to produce new groves, we'll have an even better indication."
The first signs of hemlock woolly adelgid infestation were found in the East about 50 years ago. They have killed three-quarters of the hemlocks in Shenandoah National Park in Virginia and are poised to similarly damage trees at Delaware Water Gap National Recreation Area in Pennsylvania.
The hemlock woolly adelgid is a close relative of the balsam woolly adelgid, from Europe, which has destroyed about 80 percent of Fraser firs in Great Smoky Mountains National Park.
The predator beetle has been used in other areas in attempts to control the adelgid, but its effectiveness is uncertain because the infestations in those areas were already well-established.
Learn more about the impacts of non-native species.
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