European Hornet Damage to Ash and Birch Trees

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SCRIVEN.G.T., EL. REEVES and R.F. LUCK.1986. Beetle from Australia threatens Eucalyptus. California Agriculture 40(7&8): 4-6. Since the eucalyptus longhorn borer was discovered in October 1984 infesting eucalyptus trees near El Toro, California, it has been spreading rapidly in the southern part of the state. Eucalyptus has been planted in California since the 1860s but has been free of major pests until the arrival of the borer, Phoracantha semipunctata, a cerambycid beetle. The borer is the first such pest to reach the United States from Australia, the native home of eucalyptus. One of the more common broadleaf trees in urban California, eucalyptus is potentially threatened by the beetle in landscape and woodlot plantings, especially when subjected to periodic moisture stress. Such stress, even for brief periods, increases vulnerability to attack. The beetle is a strong flyer and has been known to attack isolated trees nine miles from the nearest infested tree. Our preliminary observations suggest that eucalyptus species vary in susceptibility to attack under comparable drought conditions. Massive beetle attacks quickly kill Eucalyptus globulus and E. viminalis when their gum defenses decline. In contrast, the gum defenses of E. blakelyi continue to cause high mortality of larvae entering the bark. We are currently evaluating other species of Eucalyptus.