The plant bug Stethoconus praefectus (Distant), a member of the subfamily Deraeocorinae and tribe Hyaliodini, is reported in North America for the first time based on specimens collected on avocado, Persea americana L. (Lauraceae), in South Florida. This predatory mirid, observed feeding on avocado lace bug, Pseudacysta perseae (Heidemann), is only the second lace bug specialist established in the Western Hemisphere. The adult is diagnosed and redescribed; photographs of the adult female, SEM photomicrographs of selected structures, and illustrations of male genitalia are given to help distinguish this species. Preliminary observations on feeding habits and prey consumption of avocado lace bugs are provided.