Red Oak Borer, Enaphalodes rufulus (Coleoptera: Cerambycidae), in the Ozark Mountains of Arkansas, U.S.A.: An Unexpected and Remarkable Forest Disturbance

A complex interaction of multiple factors has resulted in an oak decline event in oak-hickory forests of the Ozark Mountains of Arkansas and Missouri, U.S.A. The most striking feature of this situation is an unprecedented population explosion of red oak borer, a species of cerambycid beetle, Enaphalodes rufulus (Haldeman), which appears to be causing extensive mortality to mature red oaks (Quercus, subgenus Erythrobalanus). The insect is a native species, historically a minor pest of oaks, found throughout the eastern United States. Beetles normally reproduce in living oaks, as larvae initially feed in phloem tissue and subsequently bore into xylem where pupation occurs. The life cycle is two years in length and synchronous adult emergence occurs in odd-numbered years. Data from previous research indicate average attack densities of less than four per tree with a high of 71 on a single tree. Historical emergence densities are similarly low and the highest reported was 15 adults from one tree. Our research is concerned with understanding factors contributing to this outbreak; developing sampling methods for red oak borer; assessing oak mortality; and evaluating site and stand conditions associated with the current outbreak. Results of our initial sampling reveal dramatically higher average attack densities of 244 per m2 and emergence densities of 18 per m2 of bark surface area. We confirm a three-week period of adult emergence and activity during mid-June to early July. We also report on possible management responses by federal and state agencies to this remarkable epidemic and oak mortality crisis.