The emerald ash borer (Agrilus planipennis) is an invasive Asian beetle, first noticed in the U.S. in Michigan in 2002, although it had probably arrived some years earlier. It has now spread to Ohio, Indiana, Wisconsin, Illinois, New York, Pennsylvania, Maryland, Virginia, and Ontario, Canada, despite attempts to keep it contained and prevent transport of ash wood; other states are on the watch for it. The ash borer rivals Dutch elm disease in its destructive capabilities. In targeting the ash, an important hardwood for wildlife habitat, for ornamental landscaping, for lumber and firewood, the potential damage to communities, businesses and property owners is far-reaching.
Life Cycle
The ash borer beetle carries out its entire life cycle in the ash tree. The adult, half an inch long and metallic green, emerges through a D-shaped hole in late spring and feeds on ash foliage. In due time, it mates and lays eggs, and new larvae penetrate the bark. The major damage to the tree comes from the larvae burrowing and feeding on the tree’s vascular system. The larvae then overwinter in the outer part of the bark and pupate in spring.
Control
Early detection, removal and destruction of infected trees may not be cost-effective, and chemical insecticides cannot be safely used over large areas. Efforts are now underway to find eco-friendly bio-management options. Several approaches are being studied.
One possibility is use of the fungus Beauveria bassiana. This is an active ingredient in a registered bioinsecticide. The fungal spores can be sprayed onto the tree when the larvae are present. The spores can attach both to the larval cuticle, causing larval death, and to the leaves, causing fatal infection in adults. Ongoing research by the USDA and Michigan State University is evaluating the effectiveness of this approach.
Three species of parasitic wasps have been observed (by U.S. Forest Service and Michigan State University researchers) in Michigan to be natural enemies of the emerald ash borer. It appears that two of the wasp species belong to the genus Balcha and feed on the borers’ larvae, and the other belongs to the genus Pediobius, which eats the eggs. However, Pediobius alone contains 215 species worldwide; 32 are found in North America. Time and effort will be needed for careful identification and propagation.
Other entomologists, with the Agricultural Research Service, are hoping to analyze the borer’s DNA. They have traveled to South Korea, Japan, and Mongolia to search for the beetle’s origin and hope to find its natural enemies as well.
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