by Ellen Goff

Stowaway bugs kill millions of trees. They pass through our nation's borders on ships and aircraft — unseen, silent and unnoticed. They settle in and begin to multiply, waiting for the day they'll be discovered.

The saga of stowaway foreign insects has repeated itself many times over for more than a century with similarly disastrous consequences. Despite rigorous inspection efforts, alien species have arrived camouflaged among vegetation, enclosed in packing materials or buried in soil used as ballast in cargo ships.

The Emerald Ash Borer (EAB), discovered in 2002 outside of Detroit, is the newest invader. Hidden away within wooden crates and pallets from Asia, EAB infestations spread through the region with the movement of nursery stock, hardwood lumber and firewood. Currently, there are outbreaks in Michigan, Ohio, Indiana, Illinois, Pennsylvania, Maryland and West Virginia.

According to the United States Department of Agriculture Forest Service, EAB is the worst tree-killing pest introduced into North America since the chestnut blight. This latest plague is responsible for the death and decline of more than 25 million trees.

One of the most frightening aspects of this scourge is that it attacks healthy, vigorous trees as well as stressed ones. The beetle lays its eggs on the tree's bark and when they hatch, the larvae tunnel into the tree to feed on vascular tissue. As the insects interrupt the flow of nutrients to the tree's crown and branches, dieback occurs. This process can continue for several years without detection, since the larvae exit holes are found high on the trunk and upper branches.

Efforts to contain the pest in affected areas and prevent its further spread are ongoing. Illinois, Indiana, Ohio and the lower peninsula of Michigan are under federal quarantine to restrict the movement of host materials. Eradication of infested and dying trees has cost millions in state funds so far, and much more will be needed before the disaster is under control. "We believe that the EAB is a risk to all the ash in North America," says Sharon Lucik, spokesperson for the USDA. "EAB is spread typically by people transporting ash logs, firewood or nursery stock that might be infested. Campers might travel hundreds of miles, bringing the infected wood with them and unknowingly infest an area far from where they originated."

While the EAB hasn't infected North Carolina, there is a native moth in Charlotte that acts like a foreign invader. The fall cankerworm is a naturally occurring pest whose numbers are normally kept in check by birds, disease and other insects. However, due to mild winters and the city's large concentration of mature willow oaks, more adult cankerworms survive through their November to February procreation period, resulting in a population explosion over the past 20 years. An annual tree banding campaign has helped protect many trees throughout city neighborhoods. But residents are bracing for another tough year of battling these bugs, especially under current drought conditions.

If you live in an infested area, be sure to visit angieslist.com to find a local landscape tree professional who can eliminate the pests.

Ellen Goff is a master gardener and environmental advocate. Aside from writing about and photographing plants, Ellen tends to a 3-acre landscape she shares with her husband, cat and border collie on the shores of Lake Wylie, S.C.