Lari's Established and Beginning to Save Hemlocks (NC)

High Country Press
December 6, 2007
By Sam Calhoun

Entomologists, or bug doctors, have used biocontrols for 100 years to control invasive pests across the world. According to Dr. Richard McDonald—entomologist, sole proprietor of Symbiont Pest Management, regular contributor to the High Country Press’s series on the hemlock wooly adelgid and former biocontrol administrator of the North Carolina Department of Agriculture—the history of biocontrols shows that if entomologists introduce an insect in an area to control invasive pests and then find it in increasing numbers for three consecutive years, then the biocontrol is established.

Biocontrol is established in Banner Elk, marking an important step in the fight to control the hemlock wooly adelgid (HWA)—a tiny insect that is killing trees thousands of times its size as it sweeps down the East Coast from Maine to Florida.

But forget three consecutive years—or three generations. McDonald, working hand in hand with Virginia Tech, Blue Ridge Research, Conservation and Development and the North Carolina State Division of Forestry, now has evidence of a fourth generation of the Laricobius nigrinus predatory beetle at Hemlock Hill in Banner Elk, a test site for biocontrol of the HWA.

McDonald first released predatory beetles at Hemlock Hill in 2003, hoping to bracket the two annual generations of the HWA with three kinds of predatory beetles. The Scymnus sinanodulus beetle and the Sasajiscymnus tsugae beetle feed on the HWA in the late spring, summer and early fall, and the Laricobius nigrinus beetle—or Lari, for short—feeds on the HWA in the winter. All three beetles have entered their fourth generation at Hemlock Hill and signs of life are returning to the HWA-infested hemlocks in the area.

“No release trees have died, and I see a lot of regrowth,” said McDonald. “Trees that survived to this point will survive. I think all these trees will be fine.”

That survival is a welcome prognosis for an infestation that has looked dire for the past few years. History of Lari Beetles at Hemlock Hill

Hemlock Hill became a test site for the establishment of predatory beetles on New Year’s Day 2003 when McDonald released 150 Lari beetles—30 beetles per tree on five trees—along the creek by Hemlock Hill, and released 150 Lari beetles—again, 30 beetles per tree on five trees—in the middle of the forest at Hemlock Hill.

McDonald has recorded increasing populations of Lari on Hemlock Hill for the last four years, and Lari has spread over nearly a square half-mile area. Not only is Lari on new trees well away from the initial release trees, but Lari is also still on the initial release trees. As the HWA numbers are decreasing on the initial release trees, however, fewer Lari are being found on those trees—a sign, said McDonald, that Lari is feeding and migrating to more infested trees and the experiment is working. How Lari Works

Annually, Lari first appears—or emerges from its ovisac—in October, after the Scymnus sinanodulus beetle and the Sasajiscymnus tsugae beetle finish their fair-weather annual work schedule and die. In October, Lari begins a three-month feeding cycle, with each Lari beetle eating 3 to 6 HWAs every day. In December, Lari begins to lay eggs. Each Lari can lay 400 to 600 larvae. Each of those 400 to 600 larvae must eat 250 HWA eggs by March to fully develop—a massive blow to the HWA summer generation.

The HWA has two annual generations—one in the summer and one in the winter. Lari feeds on the adult HWA of the winter generation from October to March and Lari’s larvae feeds on the eggs of the HWA summer generation from December to March.

“Our goal of achieving bracketing—having a natural enemy attacking every life stage—of the HWA is being realized,” said McDonald.

When Lari larvae begin to feed, they also help the cause by indirect mortality, said McDonald. Lari larvae bore carelessly through HWA ovisacs to get their fill, often loosening the HWA ovisacs’ grip on the hemlock branches and dropping them on the ground. McDonald estimates that Lari larvae eat 50 percent of HWA ovisacs on each branch and knock 47 percent of the HWA ovisacs to the ground.

When Lari larvae kill an entire branch’s infestation of HWA, they move to another branch to continue feeding.

On March 31—at the tail end of Lari’s life cycle—McDonald cut open 340 HWA ovisacs from various locations on Hemlock Hill. Of the 340, one-third contained Lari larvae. Each HWA ovisac contains between 75 and 100 HWA eggs. Because each Lari larva needs to eat roughly 250 HWA eggs to fully develop, McDonald theorizes that each Lari larva needs to eat up to 3 ovisacs of eggs. Consequently, finding Lari larvae in 30 percent of the ovisacs sampled means that the Lari larvae are feeding on two to three times that number or 60 to 90 percent of the HWA ovisacs. This finding, said McDonald, is encouraging and proves that Lari is established on Hemlock Hill and completing the job it is supposed to do.

“[Hemlock Hill] is one of the top 5, if not top 3, release sites for Lari on the East Coast,” said McDonald. What’s Next?

Individuals can also help fight the HWA.

McDonald said that local residents need to help the National Forest Service make sure that no one brings Western Hemlocks back from the American West. Western Hemlocks carry a different strain of the HWA that the three predatory beetles cannot keep in check.

McDonald is also trying to organize benefit concerts in and around the High Country—called Rock for the Hemlock—to provide money for collecting beetles from the West Coast and dispensing on the East Coast.

Homeowners, McDonald said, can plant new hemlocks under the dying hemlocks in buffer zones around creeks and streams on their own land. Hemlocks provide crucial shade for the High Country’s headwaters, creeks and streams, keeping the water temperature below 70 degrees in the dead of summer and allowing trout and fish to survive. If the hemlocks die, there is nothing to fill the void and creeks and streams and aquatic life will die off.

“If that happens, within five years we can have buffers around every watershed,” said McDonald. “It would take 30 years [if this was left to nature.]

“It’s time for us now—knowing what we know—to put the pedal to the metal.” Said McDonald.

NOTICE: In accordance with Title 17 U.S.C. Section 107, this material is distributed without profit to those who have expressed a prior interest in receiving this information for research and educational purposes.

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