Dectes texanus Leconte and Ataxia hubbardi Fisher are both indigenous to the High Plains of the USA where they share various host plants in the family Compositae. In particular, both species exploit wild and cultivated forms of sunflower, Helanthus annuus, although not to the same extent. The larval stages also occupy the same niche within the host plant, (the central pith core of the stalk) where they experience intense competition, both within and between species. Larvae are highly aggressive toward other cerambycids, with typically only one gaining control of the base of the stalk, the optimal overwintering site. We present some preliminary field and laboratory observations that delineate some important differences in the biology, ecology and behavior of these two species and the nature of competitive interactions between them. The apparently inferior competitor, D. texanus, has emerged as the more important pest species in both soybean and sunflower production, although it is now quite rare in wild sunflowers where A. hubbardii predominates.