A faunal survey was conducted to find possible biological control agents forParlhenium hysterophorusL. (Asteraceae),a serious annual weed in many parts of the world, particularly Queensland, Australia, and India. Between 1977 and 1991, most of the plant's native range in North America was surveyed from bases at Monterrey and Cuernavaca, Mexico, and Temple, TX. Two hundred and sixty-two phytophagous arthropod species were collected onP. hysterophorusby various methods including hand picking, dissection, rearing, and sweeping; 144 of these species were found to feed on the plant at some stage of their life cycle. The orders represented most abundantly were Coleoptera (33.2%), Homoptera (22.9%), Lepidoptera (20.2%), and Hemiptera (18.3%). Two fungal pathogens, Puccinia abrupta Dietel and Holway varietypartheniicola(Jackson)Parmelee andPuccinia melampodiiDïeteland Holway, were also observed. An index of similarity was used to make pairwise comparisons between the phytophagous arthropod communities on different plant taxa. These comparisons showed that the fauna ofP. hysterophorusis most similar to that of ragweeds (Ambrosiaspp.). Six insect species that were shown to be stenophagous were shipped to Australia for further testing and possible field release. One of the fungal pathogens underwent host-range testing in the United Kingdom and was released in Australia