Interspecific competition between Rhinocyllus conicus and Urophora soistitialis L on nodding thistle in Canterbury

Nodding thistle receptacle weevil Rhinocyllus conicus and gallfly Urophora solstitialis attack the capitula of nodding thistle Carduus nutans L Between 31 October and 15 December 2003 the phenology of both R conicus and U solstitialis was studied at a dryland site in Canterbury Adult R conicus were more numerous than U solstitialis on capitula throughout the experiment Larvae of R conicus were first found on 11 November (15 of capitula infested) and peaked on 2 December with 53 of capitula infested Only 3 of capitula were infested by U solstitialis Adult R conicus or U solstitialis emerged from 79 of the selected primary and secondary capitula The majority of infested capitula (81) contained only R conicus 2 contained only U solstitialis while 17 contained both insect species Parasitism of R conicus by the braconid parasitoid Microctonus aethiopoides was low and occurred when most weevil eggs had been laid