Research Plant Pathologist
former Biological Technician, North Central Forest Experiment Station, U.S. Department of Agriculture Forest Service, 1992 Folwell Avenue, St. Paul, MN 55108
Field experiments were conducted to determine whether the frequency of Ceratocystis fagacearum and Ophiostoma quercus propagule acquisition by nitidulids visiting oak wilt fungal mats is affected by the presence of O. quercus on the mats. Augmentation sprays with O. quercus were used to achieve different levels of mat colonization by that fungus. The extent of colonization by O. quercus 7 to 14 days after spraying was greatest for postmature mats with open cracks (>0.5 cm) observed on the spray date (P< 0.02). Specifically, all six subsamples assayed per mat for 16 of 18 open, O. quercus-sprayed, postmature mats yielded O. quercus. The frequency of nitidulids with O. quercus was also highest (83%) for those collected from O. quercus-treated, postmature mats that were open on the spray date. The frequency of nitidulids with viable C. fagacearum (88%), however, was also greatest for beetles from the postmature mats. Thus, O. quercus colonization did not affect vector acquisition of C. fagacearum from the mats. In addition, O. quercus vectored by nitidulids probably does not result in natural biological control of overland transmission of C. fagacearum at fresh wound surfaces on healthy oaks, as previously suggested.