Entomopathogenic nematodes are lethal endoparasites of insects. Infective juveniles actively forage and infect new hosts and are likely to encounter both uninfected and previously parasitized hosts that vary in their quality as a potential host. Although there is evidence that infective juveniles may be able to discriminate between infected and uninfected hosts, the specific chemical cues used to make these infection decisions are unknown. Changes in the volatile chemicals emitted by two model insect species (Galleria mellonella and Tenebrio molitor) at 0, 48, and 120 hours post-infection by the entomopathogenic nematode Steinernema riobrave were determined. Head space volatiles were collected by solid phase microextraction, and characterized on a Shimadzu gas chromatograph-mass spectrometer. Both qualitative and quantitative differences in a suite of compounds between infected and uninfected insects were observed. Preliminary identification of compounds was made based on mass spectra. Additional experiments will be conducted to confirm identification and evaluate the impact of these compounds on nematode infection behavior.