Differences in leafminer (Phyllonorycter, Gracillariidae, Lepidoptera) and aphid (Tuberculatus, Aphididae, Hemiptera) compositions among Quercus dentata, Q. crispula, Q. serrata and their hybridsYoshihiro Hata  Takuto Hashiba  Takashi Nakamura  Masashi Kitamura  Takahide 2 Abstract Leafminer (Phyllonorycter, Gracillariidae, Lepidoptera) and aphid (Tuberculatus, Aphididae, Hemiptera) compositions were studied in three deciduous oak species, Quercus dentata, Q. crispula and Q. serrata, and their hybrids in Tomakomai Experimental Forest of Hokkaido University, Hokkaido, northern Japan. Identification of trees in this forest was done mainly on the basis of discriminant analysis on leaf morphology with reference to trees in pure Q. dentata and Q. crispula stands and a Q. serrata stand mixed with Q. crispula. The results suggested that hybridization occurred in all combinations (i.e., Q. dentata-Q. crispula, Q. crispula-Q. serrata, and Q. serrata-Q. dentata) and the frequency of hybrids was about 10 %. The composition of Phyllonorycter and Tuberculatus species differed between Q. dentata and Q. crispula or Q. serrata, but did not differ between Q. crispula and Q. serrata. Thus, Q. dentata would differ from Q. crispula and Q. serrata in chemical properties that determine herbivore host selection, survival and performance, possibly reflecting their eco-physiological differences or phylogenetic distances. The study insects were divided into three groups; species specialized to Q. dentata (three Phyllonorycter and one Tuberculatus species), those to Q. crispula and Q. serrata (six Phyllonorycter and two Tuberculatus species), and a species collected at least from Q. dentata and Q. crispula (one Tuberculatus species). Putative hybrid trees of Q. dentata and Q. crispula harbored both Q. dentata-and Q. crispula-specific insects.