Laboratory experiments were conducted to study the behavioral activity of grain-derived volatiles as attractants and pheromone synergists forSitophilus oryzae, an internal-feeding pest of sound grain, andTribolium 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 attractive toS. oryzae at various doses, butT. castaneum were not attracted to any dose of any of these three compounds. When oils from pressed grains were bioassayed, sesame oil was significantly repellent and oat and wheat germ oils were attractive toS. oryzae. However, rice, soybean, oat, wheat germ, and corn oils were all attractive toT. castaneum. A commercial food product composed primarily of soybean oil and wheat germ was highly attractive toT. castaneum, but elicited no response fromS. oryzae. A combination of the three grain volatiles valeraldehyde, maltol, and vanillin with the synthetic pheromone sitophinone was more attractive toS. oryzae than either the pheromone alone or the tripartite grain volatile mix. Similarly, a combination of the commercial food product with the pheromone 4,8-dimethyldecanal was more attractive toT. castaneum than either food alone or pheromone alone. Behavioral 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, whileT. castaneum utilizes damaged or deteriorated grains and responds best to oils characteristic of damaged or fungus-infested grain. Synergism of food odors and pheromones suggests that more effective traps can be devised for management of these pest insects.

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