America's Forests
1999 Health UpdateOverview MapIntroduction
Issues and Examples of Forest Ecosystem Health Concerns
II. Invasion of Exotic Pests

Expanding global trade and travel have increased the risk of introducing new, exotic organisms. When brought into new ecosystems, exotic species have no natural enemies and, therefore, can cause extensive damage. Responsible for regulating the movement of plants and plant materials that may carry pest organisms and for detecting and eradicating new pest introductions, the USDA Animal and Plant Health Inspection Service (APHIS) implements quick eradication efforts for exotic pests that are not established, such as the Asian long-horned beetle. The USDA Forest Service works closely with APHIS and States to assist in action against exotic pests. For well-established exotic pests such as gypsy moth and white pine blister rust, the USDA Forest Service has established programs to protect and restore affected tree species.


Asian Long-Horned Beetle (ALB)—Introduced to the United States as larvae inside untreated wood shipping pallets from China, this exotic insect was first found infesting trees in New York in 1996, and more recently, in Chicago in 1998. The ALB feeds on 100 species of hardwoods, including elms, horsechestnut, and maple trees. APHIS, with the USDA Forest Service and many State and local partners, is leading an aggressive survey effort to detect and eradicate existing ALB populations. Infested trees are cut and destroyed. In 1999, more than 5,000 infested trees were found and destroyed in Illinois and New York. To help stop further introductions, APHIS issued regulations on solid wood packing material from China in 1998. APHIS, USDA Agricultural Research Service, and the USDA Forest Service are conducting a coordinated research and development program to provide knowledge and technology essential to more effective survey and control. The USDA Forest Service is also working to increase public awareness and participation in combating this pest.

Above: Asian Long-Horned Beetle
Right: Dead Tree–Boxelder killed by Asian Long-Horned Beetle; bark has fallen off, revealing larval galleries and exit holes

Hemlock Woolly Adelgid (HWA)—This exotic species is a major threat to hemlock trees in the Eastern United States. Mature eastern hemlock trees are an important part of evergreen forests from Maine to Virginia—serving as a major component along streams and helping to prevent soil erosion around water bodies. The HWA has spread at a rate of 20 miles per year to locations in many States on the east coast, expanding its range to the north and south in 1999. In response to the expansion, the USDA Forest Service has increased research on predators for biological control. A predaceous ladybug, discovered in Japan by a Connecticut researcher, has been tested and reared as a biological control-agent ladybug. This ladybug feeds exclusively on HWA. Mass releases of 125,000 adelgid-eating ladybugs were made in selected locations during 1999. Ladybug rearing and release continue, and preliminary results indicate a 47- to 87-percent reduction of HWA on the trees with the ladybugs. The USDA Forest Service continues its research, technology development, and other efforts to assess and predict impacts of HWA on hemlock health. It also continues to monitor the effectiveness and behavior of the released ladybugs and to monitor and investigate additional natural enemies in Asia.

Hemlock infested with Hemlock Woolly Adelgid

Pink Hibiscus Mealybug—This exotic insect was first reported in the Caribbean islands of Grenada, Saint Kitts, and Trinidad in the mid-1990’s. It has since spread to 25 more islands, including the U.S. Virgin Islands and Puerto Rico. This year, it was found on the U.S. mainland in southern California. This insect can attack over 200 plant species, including many urban, rural, and agroforest trees. It has the potential to seriously harm forests in the tropical and subtropical areas of the United States and its territories. Although the susceptibility of all plant species found on the Caribbean National Forest and elsewhere in Puerto Rico is not known, the extensive list of host plants reported from other locations is already cause for concern. The potential for damage to important forest species such as teak and blue mahoe would likely be very high.

APHIS has initiated a biological control program that identified an insect that feeds on the mealybug. They established a parasite rearing facility on St. Thomas and several field insectiaries. The use of the biological control has resulted in at least an 80-percent decrease in the mealybug population within 11 months in the treated area. The USDA Forest Service International Institute of Tropical Forestry and Forest Health Technology Enterprise Team are cooperating with the University of Puerto Rico in investigating insecticides that would kill the pest but not harm other beneficial insects. These insecticides would be used to eradicate the pink hibiscus mealybug on nursery stock shipped out of infested areas.

Pink hibiscus mealybug adult females (arrow)
Infested twig on hibiscus shrub  

Gypsy Moth—This exotic insect is a major threat to the hardwoods in eastern U.S. forests. Since its introduction into Massachusetts from Europe in 1869, the gypsy moth has spread to 17 States in the Northeast and the District of Columbia. Damage occurs in wild forested areas, suburban forested neighborhoods, and urban parks. Dead trees are a safety hazard and expensive to remove. The area already infested represents approximately 25 percent of the total area that is susceptible to this insect. It could infest much of the South and Midwest during the next 30 years if left unchecked.

Gypsy moth

In 1992, the USDA Forest Service and cooperators initiated a pilot test to determine whether the expansion of the infected area could be slowed. The test was a success and in 2000 the Slow-the-Spread (STS) strategy was implemented across the entire leading edge of the gypsy moth, from Wisconsin to North Carolina. The STS strategy is expected to reduce the gypsy moth spread by at least 60 percent. The strategy focuses on moth populations in a band between areas of widespread infestation and those that are not infested. In this transition zone, populations are low and discontinuous and can be detected with attractant-baited traps. With careful trapping, monitoring, and treatment, the advance of the insect can be slowed considerably.

In Western States, gypsy moth detection surveys are carried out by APHIS and the USDA Forest Service to find new infestations. Small populations periodically appear, but efforts to eradicate them have been successful and millions of dollars have been saved in suppression costs. Gypsy moths are typically introduced into the West by movement of household goods from infested areas in the East.

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