Insects Associated with Wounds on Trees that Develop Oak Wilt1

Abstract

In the 4-year period 1955-1958 inclusive it was found in five study plots in southeast Missouri that the incidence of oak wilt caused by the fungus, Ceratocystus fagacearum (Bretz) in black and scarlet oaks was significantly higher in trees that were blazed with an ax or wounded by boring auger holes in their trunks than it was in similar trees that were given a puncturetype wound or were not wounded. However, no infections developed in trees that were wounded before April 11 or after May 6. In all cases oak wilt developed the same season that the tree was wounded. It seems likely that such insects as sapbeetles, wood roaches, and carpenter ants carried the inoculum to the trees that developed oak wilt. This is concluded because one or more of these insects was caught in traps that were stapled in auger holes on trees that developed oak wilt. However, the source of the inoculum is unknown, because no oak wilt fungus mats or other recognized sources of the fungus were found in systematic surveys made within and around the five plots.