BEHAVIORAL-RESPONSES TO FOOD VOLATILES BY 2 SPECIES OF STORED-PRODUCTCOLEOPTERA, SITOPHILUS-ORYZAE (CURCULIONIDAE) AND TRIBOLIUM-CASTANEUM(TENEBRIONIDAE)

Laboratory experiments were conducted to study the behavioral activity of grain-derived volatiles as attractants and pheromone synergists fo r Sitophilus oryzae, an internal-feeding pest of sound grain, and Trib olium castaneum, an external-feeding pest of damaged grains and flour. Behavioral studies with two-choice pitfall bioassays determined that the fresh grain volatiles valeraldehyde, maltol, and vanillin were att ractive to S. oryzae at various doses, but T. castaneum were not attra cted to any dose of any of these three compounds. When oils from press ed grains were bioassayed, sesame oil was significantly repellent and oat and wheat germ oils were attractive to S. oryzae. However, rice, s oybean, oat, wheat germ, and com oils were all attractive to T. castan eum. A commercial food product composed primarily of soybean oil and w heat germ was highly attractive to T. castaneum, but elicited no respo nse from S. oryzae. A combination of the three grain volatiles valeral dehyde, maltol, and vanillin with the synthetic pheromone sitophinone was more attractive to S. oryzae than either the pheromone alone or th e tripartite grain volatile mix. Similarly, a combination of the comme rcial food product with the pheromone 4,8-dimethyldecanal was more att ractive to T. castaneum than either food alone or pheromone alone. Beh avioral responses to grain volatiles may reflect the ecological niche of the granivore: S. oryzae colonizes sound grain and is attracted to volatiles characteristic of fresh grain, while T. castaneum utilizes d amaged or deteriorated grains and responds best to oils characteristic of damaged or fungus-infested grain. Synergism of food odors and pher omones suggests that more effective traps can be devised for managemen t of these pest insects.