Anacardic acid (2-hydroxy-6-alkylbenzoic acid) produced and secreted from glandular trichomes of zonal geranium (Pelargonium x hortorum; Geraniaceae family) provides resistance to small pests (aphids and spider mites). To assess the potential bioactivity of anacardic acid against larger insect pests and to determine if an alternate mode of application (ingestion rather than the topical application) could impart resistance to pests, the effects of anacardic acid consumption on the development of Colorado potato beetle larvae were tested. Analysis of dose-response curves indicated a significant effect on weight gain and mortality. Assessment of food preference (treated versus untreated) indicated larvae avoid food containing anacardic acid and have a lower feeding rate on food containing anacardic acid. On the basis of these results, it is suggested that anacardic acid, applied as a chemical spray or through bioengineering production in crop plants, may provide a new tool in the arsenal to minimize damage to plants caused by pests.