The rate of preimaginal development ofHippodamia parenthesis(Say) was linearly related to temperatures from 14 to 30°C.H. parenthesisrequires 234.8 ± 10.0 degree days (±SE) above a lower developmental threshold (t) of 1O.8°C ± 1.1 to complete preimaginal development. Newly emerged adults from larvae reared at 18 and 22°C weighed significantly more ($\bar x$= 0.0095 and 0.0099 g, respectively) than adults reared at 14, 26, and 30°C ($\bar x$= 0.0085, 0.0087, and 0.0085 g, respectively). Total preimaginal development ofH. parenthesisreared at 22°C on pea aphids,Acyrthosiphon pisum(Harris) (Homoptera: Aphididae), averaged 22.0 d, significantly faster than the 23.4 d required on a diet of greenbugs,Shizaphis graminum(Rodani) (Homoptera: Aphididae). Immature survival was approximately 90% on both aphid diets. Adults reared onA. pisumwere significantly heavier ($\bar x$= 0.0098 g) and larger ($\bar x$= 3.15 mm wide by 5.31 mm long) than those reared on theS. graminumdiet ($\bar x$= 0.0068 g and 2.88 mm wide by 4.87 mm long).