The emerald ash borer, Agrilus planipennis, a small metallic beetle, native to Asia is a new pest to American soil, threatening to wipe out the entire North American population of ash trees. Scientists believe that the emerald ash borer arrived in the US in 2002 and has already wiped out over 25 million ash trees in 11 Midwestern and Northeastern states as well as two provinces in Canada. Scientists are still debating just how the emerald ash borer arrived in North America but one of the theories is that some beetles or larvae stowed away in wooden cargo crates, such as are found on commercial freighter ships and cargo planes. Big commercial shipments are typically shipped in wooden cargo crates as our different types of fruits and other foods shipped to North America from around the world.
Another possibility that could explain the beetle's arrival to the North American continent would be that it was brought here unknowingly by humans. Human activities are known to cause the spread of non indigenous insects. For example if someone visited overseas and brought home an exotic plant or if a few beetles were accidently transported out of their native country by suitcase, they could in fact reproduce, however; this scenario seems unlikely as it would take years for the emerald ash borer to grow in numbers so great to cause such an infestation as found in such a short time.
Adult emerald ash borers eat ash foliage and are harmless to well established trees however; an adult female will drill a "D" shaped hole in the bark of a healthy ash tree and lay her eggs in the bark. Once the eggs hatch the larvae feed on the inner bark of the tree, leaving behind "S" shaped tunnels, disrupting the tree's ability to transport water and other nutrients. Initially infected trees will suffer dieback, of the tree will die off. The following year the remaining under canopy will also die resulting in the entire tree dying off. Once infected, trees normally die off within two years. White ash, black ash and green ash are the only species of trees known to be effected by the emerald ash borer.
The emerald ash borer isn't the only non indigenous insect effecting native North American plant species. An insect known as a citrus pysllid is rapidly spreading a disease known as Citrus Greening throughout orange groves in Florida and is threatening to wipe out the entire US citrus industry within 10 years. Non indigenous insect infestation is a growing problem in the North America due to the large amounts of overseas shipments coming into the US on a daily basis. And with more people traveling to foreign soils than ever before it increases the chances of other non indigenous insects invading North American soil in the future.
There is currently no way to stop the emerald ash borer. Scientists are relying on public education and quarantines to control the spread of the disease. The emerald ash borer could find itself the subject of Congressional debate as the government might have to put new regulations into place on overseas shipments entering the US, to stop devastating insect infestations in the future.