Insects associated with butternut and butternut canker in Minnesota and Wisconsin

Abstract

Butternut, Juglans cinerea, is being killed throughout its native range in North America by the fungus Sirococcus clavigignenti-juglandacearum. In addition to rain splashed spores, it is thought that the fungus may have spread over long distances to infect widely scattered butternut by insect vectors. During surveys in 1995 and 1996 we found several insect species in close association with diseased butternut trees, and spores of S. clavigignenti-juglandacearum were isolated in pure culture from the bodies of some of these insects. Potential insect vectors were species in the coleopteran genera Eubulus (Curculionidae), Laemophlaeus (Laemophloeidae), and Glischrochilus (Nitidulidae). Because several insect species become contaminated with fungal spores, further study is needed to determine if any of these insects might transmit the fungus to healthy trees and thereby infect them.