Beetles Battle the Hemlock Woolly Adelgid

Hemlock Woolly Adelgid on hemlock branch.  Photo courtesy Robert L. Anderson, USDA Forest Service, Bugwood.org.

Hemlock Woolly Adelgid on hemlock branch.
Photo courtesy Robert L. Anderson, USDA Forest Service, Bugwood.org.

Dubbed the “Redwood of the East”, eastern hemlock is a long-lived and slowing growing giant that can reportedly live up to 800 years-old and reach heights of more than 150 feet. The species is considered to be the most shade tolerant tree in the Eastern US and is an ecologically important component of Southern Appalachian forests. The dense shade cast by the evergreen tree’s canopy creates critical wildlife habitat, stabilizes stream banks, and keeps mountain forests and streams cool.

Many forest and aquatic species depend on the presence of hemlocks, whose numbers have declined significantly in the past 10 years due to the introduction and spread of the hemlock woolly adelgid (HWA). In fact, by 2010 all NC counties within the historic range of hemlocks were infested. This tiny aphid-like insect has wreaked havoc on both eastern and Carolina hemlocks by literally sucking the trees dry and injecting saliva that distorts plant growth. Under high infestation rates, HWA can cause tree death in as little as four to seven years.

Close-up of HWA. Photo courtesy of Michael Montgomery, USDA Forest Service, Bugwood.org

Close-up of HWA. Photo courtesy of Michael Montgomery, USDA Forest Service, Bugwood.org

In 2014 the Hemlock Restoration Initiative, a cooperative effort launched by the NC Dept of Agriculture & Consumer Services to restore the long-term health of NC hemlocks, provided $75,000 in grant funds to WNC Communities, which in turn funded several projects to address treatment and restoration options for North Carolina’s hemlock trees.

One of the award recipients, the Blue Ridge Resource Conservation and Development Council (Blue Ridge RC&D), provides educational workshops on biological control of HWA for individuals and organizations like SAHC who steward lands impacted by HWA.  The goal of the workshops is to provide information on the benefits and use of predator beetles for HWA control. Specifically, Blue Ridge RC&D’s project intends to train workshop participants on methods for collecting and releasing predator beetles such as Laricobius nigrinus (also known as Lari beetles) that feed on HWA. The program hopes this will facilitate the spread of predatory beetles. HWA is native to Asia and the Pacific Northwest, where it also feeds on hemlocks. However, HWA is not considered to be a pest in the western US because natural enemies like Lari beetles keep HWA populations under control.

A Laricobius larva eats hemlock woolly adelgid eggs. Right: An adult Laricobius beetle. Photo by US National Park Service.

A Laricobius larva eats hemlock woolly adelgid eggs. Right: An adult Laricobius beetle. Photo by US National Park Service.

Lari beetles are effective winter predators and feed exclusively on adelgids from October to May. Each Lari larva can consume 200 to 250 adelgid eggs or crawlers before they pupate in June. In fact, research shows that the beetles can eat more than 90 percent of HWA in areas where the beetles have been released. Once established, Lari beetles can advance up to 2 miles per year.

Lari beetles have been released throughout Western North Carolina on private, federal and state lands. Recently, the NC Wildlife Resources Commission (WRC) released 50 Lari beetles on the Sandy Mush Game Lands located in Madison and Buncombe counties. SAHC is working with the WRC on a future release of Lari beetles on an SAHC-owned tract that bridges the gap between non-contiguous sections of the state-owned Sandy Mush Game Land. This property is home to numerous Canada hemlocks. Our hope is to facilitate the establishment of Lari beetles  on this property so they can be collected and redistributed to other areas affected by HWA.

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Categories: Volunteer & Stewardship Activities | Tags: , , , , , , , | 1 Comment

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One thought on “Beetles Battle the Hemlock Woolly Adelgid

  1. We own acreage near the NC border on the Tenn side South of Chilhowee Lake. For the last 5+years, we have been spraying our hemlocks that are less than 30ft with a dilute solution of 1 liter Lemon Joy Dishwashing liquid (Sams Club Size) to about 25 gallons of water. We have had good success in keeping a limited number of the hemlocks alive and very healthy with annual soakings. We hope we are not contaminating the ground water with this soapy solution but applying it from an ATV mounted pressure sprayer is a pleasant lemon scented experience. The trees we didn’t spray continued to die or get weak. We just hiked the property last weekend and see no signs of HWA on any hemlocks and all of the living hemlocks have grown stronger over the Summer. We attribute this to the last two winter cold spells. Hopefully we can keep our hemlock grottos alive going forward. Would like to get on the list for Lari beetles.

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