Callus formation and bark moisture as potential physical defenses of northern red oak, Quercus rubra, against red oak borer, Enaphalodes rufulus (Coleoptera: Cerambycidae)

The red oak borer, Enaphalodes rufulus (Haldeman), is a native wood-boring beetle implicated as a major contributor to recent high levels of oak mortality in northern Arkansas. Northern red oaks, Quercus rubra L. (Fagaceae), were grouped into three classes of red oak borer infestation history based on crown condition and basal red oak borer emergence holes: class I (low infestation), class II (moderate infestation), and class III (high infestation). In 2004 and 2005, trees from each class were mechanically wounded and callus formation was measured after one year. Class I trees exhibited significantly greater callus formation than class III trees in both years. Monthly measurements in spring and summer of 2006 indicated significant differences in callus formation among classes, with class I trees healing over significantly earlier. Moisture was measured in bark samples removed 1 week and 4 weeks after initiation of three treatments: control, mechanical wounding, and artificial insertion of larvae. Moisture levels did not vary among infestation classes or treatments. This research indicates that bark moisture is likely not a defense against red oak borer, but that callus overgrowth may be a defense early in the second year of the life cycle in healthy trees.