Lysiphlebus testaceipes(Cresson) did not demonstrate a preference for biotype C greenbug,Schizaphis graminum(Rondani), susceptible or resistant sorghum entries in either release-capture or olfactometer tests. However, the mummy-green bug ratio for susceptible ‘Chilocco’ oats was significantly lower than for susceptible ‘Triumph’ wheat or ‘BOK-8’ sorghum in free choice tests. In olfactometer tests the percent response of the parasitoid to resistant CI-1580 oats was significantly greater than the response to susceptible Chilocco oats. No other differences between response to green bug resistant and susceptible plant entries were significant. With regard to the host plant response ofL. testaceipes, greenbug resistance was not detrimental and, in the case of oats, the response of the parasitoid may be enhanced.