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An unexpected outbreak of a native longhorned beetle, the red oak borer (Enaphalodes rufulus (Haldeman)), occurred in upland oak forests of Arkansas, Missouri and Oklahoma ca. 1999–2005. Few management tools exist for reducing E. rufulus populations. Laboratory bioassays were conducted to determine susceptibility of all E. rufulus life stages to the fungal pathogen Beauveria bassiana Vuillemin. Egg, neonate, early-instar, pupal, and adult stages of E. rufulus were all susceptible to a natural isolate of B. bassiana collected from E. rufulus (ARSEF 7404) or a commercial B. bassiana product, BotaniGard®. In July 2003, 10 living, E. rufulus-infested northern red oak (Quercus rubra L.) boles were sprayed with a 2 L BotaniGard® B. bassiana suspension of 1.3 × 1011 viable conidia per 2 m of each bole at a forested site in the Ozark National Forest, Franklin County, Arkansas. The following spring, trees were removed and sampled for E. rufulus larvae that had survived or died during the winter. Live E. rufulus larval density in untreated Q. rubra log samples was significantly greater than in treated log samples with means of 16.4 ± 1.8 (SE) and 4.4 ± 2.0 larvae per m2 of bark for untreated and treated logs, respectively. Application of B. bassiana spray against early-instar E. rufulus would be most effective in mid-summer of odd-numbered years to target vulnerable early E. rufulus life stages and to reduce structural damage to trees caused by E. rufulus feeding. |
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