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The Argentine root-boring weevil Heilipodus ventralis(Hustache) is a candidate for biological control of the perennial snakeweeds Gutierrezia sarothrae(Pursh) Britton and Rusby and G. microcephala(DeCandolle) A. Gray, poisonous native weeds of rangelands of the southwestern United States. In Argentina, the weevil occurs in semiarid regions from Tucumán south to Chubut, which are climatically similar to broad areas of the southwestern United States. Laboratory-reared females lived ca. 112 days and laid ca. 117 eggs. The eggs hatched in ca. 15 days. The larvae had eight instars; they required ca. 151 days and pupae ca. 27 days to develop. Adult weevils emerged from the taproots in early summer, fed on the leaves and terminals, and oviposited mostly in the crown near the soil line. The feeding of one or more pairs of caged adults killed medium-sized plants. The larvae tunneled downward to the taproot where they pupated. They overwintered in the taproots of these perennial host plants and pupated in the spring. A generation required 1 year but some individuals probably required two growing seasons. At Peninsula Valdés, Chubut, H. ventralispreferred Gutierrezia solbrigiiCabrera to Grindelia chiloensis(Corn.) Cabrera by a ratio of 1.9 to 1.0. In the field there, crowns of large Gu. solbrigii(average 60 cm canopy diameter) contained an average 5.0 larvae per plant, those of small plants (23 cm diameter) contained 1.1 larvae, and plants smaller than 10 cm rarely contained larvae. No insect parasitoids or predators were found attacking any stage. H. ventralisprobably evolved on xerophytic, temperate Astereae, from ancestors of the genus Heilipusthat fed on species of ancient, hygrophytic, tropical plant families.