Fourteen clerodane-type diterpenoids isolated from plants in the genera Baccharis, Teucrium, and Salvia were assayed for antifeedant activity against Tenebrio molitor larvae in order to establish structure-activity relationships. Among the compounds tested, furanoditerpenes with alpha, beta-unsaturated-gamma-lactone moieties, or C-4-epoxy substitution with C-5-methylacetoxy or C-12-acyloxy functionalities, exhibited maximal antifeedant and repellent activities.