Greenbug,Schizaphis graminum(Rondani), biotypes were studied by comparing biological data to total esterase activity levels measured by fluorescent microscopy. Also, total esterase activity was evaluated in relation to host plants and insecticide resistance. The intensity of fluorescence was measured from tarsi of large embryos after staining with fluorescein diacetate. Biotypes on susceptible ‘Wheatland’ sorghum produced significantly more and larger progeny than those on resistant KS 30 or PI 264453. Furthermore, there was a carryover effect of the previous host plant on progeny production. Greenbugs reared on resistant plants had a higher level of fluorescence compared with those on susceptible plants. Increased fluorescence was also found in separate insecticide-resistant colonies of greenbugs. However, no significant differences in esterase activity as measured by fluorescence were found among biotypes reared on the same cultivar.