The tachinidLixophaga diatraeae(Townsend) senses the larviposition host (sugarcane borer,Diatraea saccharalis)frass by tarsi rather than by antennae. Methanol extraction of the host larvae frass, followed by column and thin-layer chromatography, indicated activity in the polar nonvolatile components. Similar extraction of sugarcane stalk produced an equally active larviposition stimulant having the same chromatographic properties as the frass extract. The active fractions of both frass and sugarcane did not contain sterols, reactive unsaturation, or protein. Qualitative tests showed the presence of phenols, alcohols, and carbohydrates. The tachinid was equally active to a dichloromethane extract of paraffin wax and standard hydrocarbons alone and in combination.