INTERACTIONS BETWEEN HOST PLANTS, ENDOPHYTIC FUNGI, AND A PHYTOPHAGOUS INSECT IN AN OAK (QUERCUS-GRISEA X QUERCUS-GAMBELII) HYBRID ZONE

We examined interactions between host plants, endophytic fungi, and le af-mining moths (Phyllonorycter sp.) in an oak (Quercus grisea x Q. ga mbelii) hybrid zone. The community of endophytic fungi and two common endophyte species examined responded to host plant hybridization. Tota l fungal frequency (TFF) and frequency of Gnomonia cerastis were lowes t on hosts resembling Q. grisea, and increased linearly towards those resembling Q. gambelii. In contrast, Coccochorella quercicola was most frequently isolated from Q. grisea-like hosts and decreased in freque ncy across hybrids towards Q. gambelii. Frequency of G. cerastis and T FF covaried with Phyllonorycter density across the hybrid zone, but di rect effects of endophytes on Phyllonorycter density were not detected . Associations between endophytes and unexplained mortality of Phyllon orycter varied according to endophyte species and stage of Phyllonoryc ter development. In the sap-feeding stage, unexplained mortality was n egatively associated with TFF and frequencies of Hormonema sp. and Pre ussia funiculata; whereas, in the tissue-feeding stage, unexplained Ph yllonorycter mortality was positively associated with G. cerastis freq uency. Three-way interactions between plant hybridization, endophytic fungi, and the insect herbivore were not significant.