Bio-Control Project Shows Promise in Maryland

Predator Insect Populations Growing to Control Hemlock Forest Pest

ANNAPOLIS, MD (Oct. 4, 2010) – Deep in the hemlock forests of Maryland, Biff Thompson and Craig Kuhn, forest health inspectors from the Maryland Department of Agriculture (MDA) and Brad Onken, a forest entomologist from the U.S. Department of Agriculture (USDA) Forest Service are recovering Laricobus nigrinus, a tiny “lady bug” beetle.  These insects, about the size of a poppy seed, are natural predators of the Adelges tsugae, or hemlock woolly adelgid (HWA), a serious exotic, invasive pest of hemlock trees.   The beetles were released in an effort to control the spread of the destructive insect.

“We are very excited to find these beneficial insect populations growing rapidly and thriving where they were released. This is encouraging news in the effort to stop the spread of the hemlock woolly adelgid and the damage it causes to Maryland’s important hemlock trees and associated ecosystems,” said Agriculture Secretary Buddy Hance. “Together with our state, federal and academic partners we are finding innovative ways to protect the environment for generations to come and to help keep Maryland smart, green and growing.”

Without any natural controls, such as predators or disease, HWA populations often go unchecked, resulting in hemlock decline and death. The hemlock forests of Maryland are part of a unique and often fragile habitat. Hemlocks are usually found growing in riparian areas or in steep cove forests in the northern and western tier counties of Maryland. It is estimated that more than 42,000 acres of such forests exist in Maryland. Of special concern are a number of undisturbed stands of large hemlocks in Garrett County.

The hemlock woolly adelgid, a small exotic insect native to Asia, was discovered in Virginia in 1951 and has slowly spread along the east coast of the United States. The insect was found in landscape hemlocks in the Baltimore and metropolitan Washington areas of Maryland in the 1980s and has spread to natural stands across Central Maryland finding its way to Garrett County by 2001.  The hemlock woolly adelgid is most easily recognized by the white “woolly” wax they produce on young hemlock twigs. The “wool” is present all year, but is most abundant and conspicuous during the spring and fall when egg masses are present. Fully grown adults are only about the size of a period on a printed page.

“We are taking a two-pronged approach to control these pests by implementing biocontrol and suppression using insecticides. So far, the predator beetles are the best long term hope for management of the hemlock woolly adelgid, especially in remote natural stands of hemlock, said Bob Tatman, program manager of MDA’s Forest Pest Management Program.”

The Maryland Departments of Agriculture and Natural Resources have developed a Hemlock Woolly Adelgid Management and Suppression Plan. This plan sets forth management options for HWA on public lands across the State. Beginning in 1999 with funding and technical support from the USDA Forest Service, MDA evaluated predators for control of HWA, all of which are very small beetles in the same family as “lady bug” beetles familiar to gardeners. Since that time, MDA Forest Pest Management staff have been releasing biocontrol beetles to suppress the hemlock woolly adelgid.

Since 1999, MDA has released three different species (Sasajiscymnus tsugae, Laricobius nigrinus, Scymnus sinuanodulas) totaling 49,358 beetles in 27 locations in Harford, Baltimore, Frederick, Washington, Allegany and Garrett counties. Of the three species released, Laricobius nigrinus has already been established at seven of the 10 release sites.   The other three sites are the most recent release locations and population levels have not met the requirements to be considered established.  MDA will continue to release this species and monitor for establishment. Sasajiscymnus tsugae and Scymnus sinuanodulas were never recovered after release and have been dropped from consideration for bio-control releases in Maryland.

In addition to the biocontrol beetles, MDA has been implementing a suppression program using insecticide since 2004.  To date, MDA has treated 719 trunk injected trees since and more than 4,450 soil injected trees in Baltimore, Frederick, Garrett, Harford, and Washington counties.

MDA is currently undertaking its largest HWA suppression project to date with a goal of treating more than 5,000 trees in Harford, Baltimore, Frederick, Allegany and Garrett counties between spring 2010 and spring 2012.

Additional information about the hemlock woolly adelgid can be found on the following websites:

•   www.mda.state.md.us/plants-pests/forest_pest_mgmt/cooperative_forest_health_program/hwa.php

•    http://na.fs.fed.us/fhp/hwa/ 

•    www.fs.fed.us/foresthealth/technology/pdfs/FS_hwa.pdf

For further information, contact Bob Tatman, Maryland Department of Agriculture, Forest Pest Management Program at (410) 841-5922.

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