Sap beetle species (Coleoptera: Nitidulidae) visiting fresh wounds on healthy oaks during spring in Minnesota

Many species of sap beetles have been implicated as vectors of the oak wilt pathogen, (Ceratocystis fagacearum), but the species responsible for most aboveground transmission of the fungus is unknown. The abundance of adult sap beetle species inhabiting <7-day-old, artificially made wounds on healthy oaks during Apr.-June of 2 years in Minnesota, and the frequencies with which viable propagules of the fungi were present on each, were determined. Sap beetles were most abundant on wounds created in May, and 1-3-day-old wounds yielded higher numbers of insects than 4-6-day-old wounds. Of the beetles collected, >95% were Colopterus truncatus and Carpophilus sayi. C. fagacearum was isolated from 75% of 594 adults assayed for the fungus. The average number of viable propagules for pooled data of individuals of each species ranged from <100 to 18,000. Frequencies of fungus isolation differed by days after wounding, study location, and sap beetle species. These results, when coupled with previous findings on predominant species associated with oak wilt fungi mats, support the hypothesis that Co. truncatus and Ca. sayi are the principal sap beetle species transmitting C. fagacearum from diseased to healthy oaks in Minnesota.