Live Oaks, New Hosts for Odontocynips Nebulosa Kieffer (Hymenoptera: Cynipidae) in North America
A study of root-feeding insects as potential vectors of the oak wilt fungus Ceratocystis figaceurum (T. W. Bretz) J. Hunt in live oaks, revealed root galls induced by the cynipid gall wasp Odontocynips nebulosa Kieffer. The incidence of the wasp on roots of four oak species and natural live oak hybrids at 14 root excavation sites in 7 counties throughout the Hill Country of central Texas was surveyed. The study was limited to sites within and adjacent to oak wilt infection centers of the live oak-Ashe juniper ecotype where oak wilt infected live oaks were being uprooted and rogued for disease suppression by the Texas Oak Wilt Suppression Project. This is the first report of this root-galling wasp on live oaks, Q. fusiformis Small and Quercus virginiana Miller X Quercus fusiformis natural hybrids, in North America. The incidence of root-galling by the wasp occurred at relatively low levels among trees examined at excavation sites in each county, indicating a sporadic distribution throughout the region. However, examinations of root-colonization and gall induction by O. nebulosa in uprooted live oaks showed relatively high levels of root infestations in some trees, including trees exhibiting symptoms of oak wilt disease. This pattern suggests high population densities in small localized areas. Examinations of individual gall clusters formed by the wasp on live oak roots revealed new details of gall morphology and developmental stages of the insect within galls. The significance of this wasp as a potential vector of the oak wilt fungus is discussed.