Cotesia kariyai first recognized a host habitat through antennal perception of volatile substances from the plant fed on by host larvae, and examined the feeding traces by antennal contact with the plant. The characteristic arrestment behavior was also elicited when the wasp found exuviae and fecal pellets of host larvae. The arrestant was confirmed to he a mixture of 2,5-dialkyltetrahydrofurans which was bioassayed using a filter paper disc. When the arrestant was applied to a small glass rod, C. kariyai responded with ovipositor stabbing. A similar composition of 2,5-dialkyltrtrahydrofurans to those in extracts of the feces and exuviae was confirmed in extracts from cuticular wax of Peudaletia separata larvae. A mixture of hydrocarbons was the major component of the cuticular wax, and results of the bioassay showed a similar oviposition stimulant activity. The same compounds from different sources acting as an arrestant and as an oviposition stimulant were identified using different materials as the substrates for the bioassay.