Volatile compounds and odors in grain sorghum infested with common storage insects

Lesser grain borer (Rhyzopertha dominica), red flour beetle (Tribolium castaneum), rice weevil (Sitophilus oryzae), saw-toothed grain beetle (Oryzaephilus surinamensis), and rusty grain beetle (Cryptolestes ferrugineus) were placed in sorghum (1 kg, 14% mc) for 5, 7, and 10 weeks at 27 degrees C. Infested samples were analyzed for insect numbers, frass, odor, and volatiles. Volatiles from whole grain at 60 degrees C were collected on Tenax absorbent, thermally desorbed, and analyzed by gas chromatography using infrared and mass detectors for component identification. Odor was assessed by sensory panels at the Federal Grain Inspection Service and in flour beetle caused some off-odor. The other three insects caused little or no objectionable odor, even though infestation was heavy. High concentrations of 2-pentanol and the known aggregation pheromones, dominicalure 1 and 2, were consistently present in samples infested with lesser grain borer. These compounds were only a partial cause of the odor from lesser grain borer. Several metabolites from lesser grain borer not previously reported were tentatively identified. The presence and absence of some previously reported insect pheromones and metabolites are discussed.