H.A. Cordo

Occurrence of snakeweeds (Gutierrezia: Compositae) and their natural enemies in Argentina: Implications for biological control in the United States

Abstract Snakeweeds, Gutierrezia spp. (Compositae), are native plants that are serious weeds in rangelands of the southwestern United States and northern Mexico. Although the genus apparently originated in North America, 7 species occur in Argentina and 5 in Chile. In Argentina, we found 79 species of insects, 1 mite, and 1 plant pathogen on the 3 species of Gutierrezia most similar to the North American snakeweeds; 33 of these species were observed feeding or had a high probability of feeding on Gutierrezia . Of these, 17 species of insects appear to have narrow host ranges and are possible candidates for biological control of snakeweeds in the southwestern United States. The insects that caused the most obvious damage were 5 species of root borers: the sesiid moth Carmenta haematica (Ureta); the weevil Heilipodus ventralis (Hustache); and 3 buprestids, Dactylozodes alternans Chevrolat, D. okea Gory, and Agrilus leucostictus Klug. Other insects that may have biological control potential were two species that fed on flowers and seed heads, a pyralid moth ( Homoeosoma n. sp.) and a tephritid fly ( Trupanea patagonica (Brethes)); a leaf beetle ( Stolas ingrata (Boh.)); and 2 species of stem-gall formers, an unidentified gelechiid moth and a tephritid fly, Strobelia baccharidis Rondani. The factors that may limit control, the ecosystem effects of controlling these native plants, and the approaches that can be taken are discussed.