Monoterpenoids are found in essential oils from numerous plant families. Octopamine is a biogenic monoamine found within various invertebrates, including insects. Octopamine exerts its physiological effects through the activation of G-protein-coupled receptors (GPCRs). GPCRs are an under-utilized receptor target in the agrochemical industry. Here we report the expression of an octopamine receptor from the brain of the American cockroach (Periplaneta americana) inSaccharomyces cerevisiae, creating a ligand-independent histidine-auxotrophic assay. The majority of monoterpenoids acted as an inverse agonist in this system. Three QSAR models show that electronic properties are most important for monoterpenoid interaction with this octopamine receptor in this yeast assay.