THE DISTRIBUTION AND ABUNDANCE OF ALIEN, HOST-ALTERNATING ANDRICUS SPP (HYMENOPTERA, CYNIPIDAE) ON QUERCUS SPP (OAK) IN IRELAND

Four alien, host-alternating cynipids (gall-wasps), Andricus quercusca licis, A. kollari, A. lignicola and A. corruptrix, are present on oak in Ireland. The first three species are much more widespread within th e island than published records and putative dates of introduction sug gest; A. corruptrix is still rare and scattered (e.g. Kerry and Dublin ). The probability of finding A. quercuscalicis at a site was increase d by the presence of Turkey oak and was influenced by geographic locat ion (higher in the east and the south). For A. kollari, the probabilit y increased with southerliness and with the presence of certain other cynipid species (Neuroterus numismalis, A. curvator and A. lignicola). For A. lignicola the probability increased with easterliness and with the presence of the other two common alien gall-formers, A. kollari a nd A. quercuscalicis. While it is impossible to separate the effects o f differences in dispersal ability from differences in the length of t ime that species have been found in Ireland, the distributional limits of the three commoner alien gall species, coupled with their frequenc y of occurrence within these distributional limits, suggest that A. qu ercuscalicis exhibits the lowest rate of spread and that A. lignicola exhibits the highest. A. kollari can be found a long way from the near est Turkey oak and has almost certainly been in Ireland for the longes t period. The species richness of oak-feeding cynipids (native and ali en) was greater in eastern Ireland, probably as a result of higher pop ulation densities of oak, and higher in sites where more species of oa k were present. Of the four kinds of oak, it was the presence of Querc us robur and Q. cerris that had the largest positive effect on cynipid species richness.