Effects of Host-tree Traits on the Species Composition and Density of Galling Insects on two Oak Species, Quercus crispula and Quercus serrata (Fagaceae)

Abstract

To clarify the factors that determine the community structure of galling insects, we examined the effects of host-tree traits such as phenology and leaf quality on the species composition and densities of galling insects on sympatric oak species, Quercus crispula and Quercus serrata. Host-tree traits differed between species. In total, we recorded 23 sorts of gall: 18 from Q. crispula, 15 from Q. serrata, and 10 from both. Species composition and gall densities varied with tree species. There were no significant correlations between bud-burst phenology and the gall density on individual trees in either species for cynipids, but there were significant correlations for cecidomyiids. Synchronization of insect life history with bud-burst phenology is likely to be more critical for cecidomyiids than for cynipids, probably due to the shorter life span of cecidomyiid adults. There were no significant correlations between gall density and water content, total nitrogen concentration, or tannin astringency for any insect. These results suggest that the difference in bud-burst phenology between tree species and the difference in the response to bud-burst phenology among galling insects can cause the observed difference between tree species in the community structure of galling insects.