The greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae), is a major aphid pest of small grains and sorghum, Sorghum bicolor (L.) Moench. Greenbugs extract juice and inject toxin, killing seedlings or limiting the yield of older plants. Understanding greenbug biology and how biotypes develop is important for evaluating and developing sorghum with durable resistance. Prereproductive period, fecundity, and longevity of greenbug biotypes E and I were assessed on susceptible ‘RTx430’ sorghum at four cycling temperatures of 10–23, 14–27, 18–31, and 22–35°C in an incubator. A photoperiod of 14:10 (L:D) h corresponded with daily warm and cool temperatures. Greenbug fitness was more affected by temperature than biotype. Greenbug prereproductive period, total fecundity, and longevity did not differ among temperature regimes except at the warmest regime (22–35°C), at which all parameters were greater for biotype E than biotype I. The prereproductive period of greenbug biotypes E and I combined was more than twice as long at the coolest temperature of 10–23°C as at 22–35°C. Greenbugs produced a maximum average of 3.3 more nymphs per day at warmer than cooler temperature regimes. Average total fecundity was greatest at 10–23°C, with fewest nymphs being produced at 22–35°C. Longevity of greenbug biotypes E and I combined was 6 times longer at 10–23°C than at 22–35°C. This study provides information on optimal temperatures under which to evaluate damage to sorghum being developed for resistance to different biotypes of greenbug.