Tuesday, November 20, 2012

Oak killer

The goldspotted oak borer, Agrilus auroguttatus, is a woodboring beetle best known for destroying stands of oak trees in San Diego County, California, in the United States. This pest is native to southeastern Arizona, although a related species occurs in southern Mexico and northern Guatemala. Little is known about the life history of the insect, whether it is introduced or moving into the area as part of a natural range expansion, nor do we know anything about its current distribution. What is even more puzzling is the fact that it has never been known to cause the kind of oak destruction as it was observed in California. As of 2010, Agrilus auroguttatus has killed an estimated 21,500 trees covering 1,893 square miles in San Diego County but some estimates put the numbers at 80,000 trees.

So far the problem was restricted to San Diegio County but now the species was found 65 km north in Riverside County which is very alarming for local authorities. Larvae extracted from under the bark of a recently-killed California black oak were subjected to DNA analysis at the University of California Riverside and confirmed to be Agrilus auroguttatus

As for the one discovered in Riverside County it is believed to have made the jump from San Diego through the movement of infested firewood. It is my hope that this was an isolated find and the early discovery helps to stop it from spreading further North. Its close relatives, the emerald ash (Agrilus planipennis) and bronze birch borer (Agrilus anxius) have caused more than enough havoc among North American trees. This species now poses a major threat to susceptible oak species throughout California, southern Oregon, and beyond. Currently there are no effective tools for protecting trees once infestation occurs.

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