EFFECTS OF PUCCINIA-CARDUORUM ON MUSK THISTLE HERBIVORES

Puccinia carduorum Jacky, a rust fungus recently introduced into the U nited States for biological control of mush: thistle (Carduus thoermer i Weinmann), may interact with three established thistle herbivores, T richosirocalus horridus (Panzer) (Coleoptera: Curculionidae), Rhinocyl lus conicus Froelich (Coleoptera: Curculionidae), and Cassida rubigino sa Muller (Coleoptera: Chrysomelidae). Tests were conducted to determi ne the effects of P. carduorum on feeding, oviposition, longevity, egg production, egg hatch, and larval development of the three insects. W hen offered both rust-infected and healthy musk thistle leaves, adults of C. rubiginosa and T. horridus consumed significantly more healthy than infected foliage. On infected leaves, feeding and oviposition wer e confined largely to pustule-free areas. The amount of rust-infected and healthy foliage consumed by C. rubiginosa larvae was not significa ntly different, but feeding on the infected leaves was again confined to rust-free leaf areas. Rust infection did not reduce oviposition by the three insects, and R. conicus oviposited only on healthy portions of the bracts. There were no significant differences in longevity, egg production, percentage of egg hatch, and larval development for any o f the three insects fed continuously with both healthy and rust-infect ed leaves. Thus, effects of P. carduorum on the herbivores were slight , and among the interactions that were found, none is expected to be d etrimental to biological control. (C) 1996 Academic Press,Inc.