BELOWGROUND HERBIVORY IN CARDUUS NUTANS (ASTERACEAE) AND THE POTENTIAL FOR BIOLOGICAL-CONTROL

The impact of root-feeding insects attacking the 'biennial' Carduus nu tans L. in the southern part of ifs native European distribution was s tudied as part of a biological control programme against this weed for Australia. Surveys were conducted from Spain to Greece to parallel pr evious studies in central Europe and three populations of the weed wer e monitored in detail over a 2-4-year period in southern France. The d amage levels and attack patterns of each insect species were recorded The most common species damaging the roots and meristems were the weev ils Hadroplontus (= Ceutorhynchus) trimaculatus F. and Trichosirocalus horridus Panzer and the syrphid fly Cheilosia corydon Harris (= gross a Fallen). In manipulative experiments, made to assess their impact on the host plant, C. corydon reduced seed production by up to 45%, whil e the two weevils mainly altered plant architecture. The results are d iscussed in relation to previous experience of using root feeders for the biological control of G. nutans.