Hitchhiking Bugs

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Published on: Mar. 2, 2007

Last revision: Nov. 30, 2010

ash borer arrived, ash trees in the Midwest were battling native pests. It is common to see ash trees with symptoms of ash yellows (a disease) or ash decline, a condition caused by a variety of diseases or other stresses. Native wood-boring insects frequently attack ash trees stressed by injury, transplanting, soil compaction or poor tree location. All of these problems can result in branch dieback, sparse leaves and gradual decline of tree health over several years.

Because of these ongoing problems, it’s not easy to know if a tree has been attacked by the emerald ash borer. One of the most distinctive clues to look for is a 1/8-inch diameter, D-shaped hole in the bark that the adult emerald ash borer creates when it exits a tree.

Pathways for Invaders

Once an invasive insect species gains a foothold in North America, it can move by many pathways across the continent. Emerald ash borers traveled in firewood from Detroit to recreation sites throughout Michigan and nearby states. They hitchhiked in logs transported to sawmills and in nursery stock shipped from Michigan to Maryland.

Asian longhorned beetles, another non-native wood borer, traveled in firewood from infested trees cut down in Brooklyn to uninfested forests on Long Island.

Gypsy moths, which defoliate oaks, temporarily established themselves in northwestern Arkansas in the early 1990s, possibly after hitchhiking from the northeastern U.S. as egg masses attached to recreational vehicles. Aggressive action by state and federal authorities eradicated the gypsy moth population in Arkansas, but the infested area of the northeastern U.S. continues expanding westward and will eventually reach Missouri.

Asian longhorned beetle populations have been nearly eradicated in Chicago, and eradication efforts continue against populations in New York, New Jersey and Ontario. However, eradicating the emerald ash borer is very unlikely because of its wide distribution and the lack of effective means to detect and control it.

Insects are not the only forest pests that can be transported in firewood and other plant parts. Tree diseases such as oak wilt and Dutch elm disease can easily hitchhike, too, and are even more difficult to detect.

Protecting Our Forest Resources

New national and international regulations specify treatments for solid wood packing materials that will reduce the threat of hitchhiking pests in international trade. Incoming cargo is examined for potential pests at U.S. ports by federal inspectors, although only a small fraction can be inspected because of the huge volume.

Working together, the Missouri Departments of

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