Abundance Patterns and Species Richness of the Parasitoids and Inquilines of the Alien Gall-Former Andricus quercuscalicis (Hymenoptera: Cynipidae)

Abstract

1) Four parasitoid species attack the gall-maker in the agamic galls of the invading cynipid Andricus quercuscalicis and further two parasitoid species attack inquiline larvae developing in the parenchymatic wall of the gall. The abundance of the parasitoids and inquilines are correlated with: 1) gall morphology; 2) the geographical location within Europe where the samples were collected; and 3) the abundance of other members of the species complex. 2) The invading gall wasp has been present for different periods of time at different sites, and this is likely to affect the geographic distribution of attack by parasitoid and inquiline species. One of the parasitoid species was restricted to the native range in south-eastern Europe (Aulogymnus trilineatus), while another species (Cecidostiba hilaris), a parasitoid of the inquilines, was present throughout continental Europe but is not yet recorded from the British Isles. Species richness of the parasitoid complex associated with the galls of A. quercuscalicis declined with increasing distance away from the native range. Within the native range, however, species richness was negatively correlated with the total number of cynipid species (alternative hosts for the parasitoid species) recorded at the same sample site. 3) The size of mature knopper galls declined westwards and northwards away from the native range of the gall wasp. Inquiline abundance was higher in larger galls, and so was the occurrence of one of the parasitoid species, Megastigmus stigmatizans. The occurrence of two other parasitoid species was negatively correlated with gall size while one species, Mesopolobus jucundus, was not affected by gall size. 4) Neither the abundance of inquilines nor of parasitoids attacking the inquilines show any significant geographical trend associated with the invasion history of the gall-maker. Attack rates by C. hilaris, the dominant parasitoid species in continental Europe, showed a slight positive density dependence to the number of inquilines per gall, while those by M. jucundus, the dominant parasitoid of inquiline in Britain, showed no such trend.