Seasonality, abundance, species richness and specificity of the phytophagous guild of insects on oak (Quercus) canopies

1. A study was made by knockdown sampling and branch clipping of the arthropod fauna of two native oaks (Quercus petraea and Q. robur) and of two introduced species (Q. cerris and Q. ilex) in woods near Oxford, U.K., and of two native species (Q. ilex and Q. pubescens) in southern France. Sampling was undertaken for five years in England and four years in France. All the phytophagous species except Acarina and Cecidomyidae from the Oxford samples were identified to species.2. In England a marked seasonal pattern was observed in all years: chewing insects peaked in May, followed sequentially by sucking species, leaf miners and gall formers. The May peak on the native trees is much larger in terms of individuals, and especially in biomass, than on the introduced species. This peak is well known to provide an important food source for several species of woodland bird. 3. Most phytophages were much less abundant on the introduced oaks than on the native species. This is probably due more to the features of the leaves, than to the introduced status per se. 4. The species richness of the fauna was estimated by three methods on the basis of the total projected number of species (Smax), and its specificity to oak by reference to the known host range as recorded in the standard reference works. 5. The species richness of Heteroptera and Coleoptera on the deciduous oaks in their natural habitats (Q. petraea and Q. robur in England, Q. pubescens in France) are similar. 6. The fauna of the evergreen Q. ilex has a similar species richness both in France, where it is native, and in England, where it is introduced and where its phytophage guild is smaller than that of the deciduous species. In England the extent of oak specificity on Q. ilex is less than that of the deciduous species. 7. In England the phytophage fauna of the deciduous and introduced Q. cerris has a species richness considerably greater than that found on Q. ilex, but somewhat less than that of the deciduous and native oaks. However, the specificity of this fauna to oaks was not significantly different to that of the fauna on the native oaks.