Gaseous emissions were analyzed by gas chromatography to determine whether increased volatile hydrocarbon production from wheat,Triticum aestivumL., seedlings infested with greenbugs,Schizaphis graminum(Rondani), was associated with virulence. Ethylene production from wheat seedlings was stimulated by greenbug infestation. Ethylene production was greater from virulent combinations of wheat genotypes and green bug biotypes, compared with avirulent combinations, in most cases. A 6-h interaction period was sufficient to trigger increased ethylene production with evolution rates decreasing sharply by 1 d after removal of greenbugs. No other stress volatiles were detected from infested seedlings, although membrane damage (based on electrolyte leakage), chlorosis, and necrotic spots were evident after 4 d in a susceptible genotype. Wheat seedlings were capable of producing increased levels of volatile hydrocarbons in response to stress because exposure to 55 or −70°C produced more acetaldehyde, ethane, ethanol, methanol, and pentane than controls.