The bionomics ofPhrydiuchus tauWarner associated with the rangeland weed Mediterranean sage,Salvia aethiopisL. (Lamiaceae), in Idaho was evaluated. The phenology ofP. tauwas closely synchronized with that of Mediterranean sage. Adults emerged from pupation in Mayor June and fed on the rapidly growing foliage of the plant rosettes until mid-June. Estivation occurred throughout the summer when plants were dormant, and adults emerged in the autumn to feed and reproduce. Oviposition occurred from November to April with eggs oviposited singly or in groups of two to four externally in the leaf axils, on the petioles, or on the leaf or crown surfaces. Larvae developed through three instars inside the crown or leaf axil. Pupation occurred in earthen cells between May and June. Larvae often completely destroyed the crown and associated meristematic tissues, resulting in the growth of new shoots and prolonging the longevity of the plant. Larvae were found in plants ranging in size from 1.6 to 43.1 mm crown diameter. Up to 35 larvae were recovered from a Single crown. Smaller-crowned plants were attacked less frequently than larger-crowned plants.