The effects of temperature on developmental rate (stage specific and total), survival, fecundity, longevity, sex ratio, and nymphal size of Siphoninus phillyreae (Haliday) were studied in environmental chambers at constant temperatures. Temperature had significant effects on developmental rate, survival, fecundity, female longevity, and size of female nymphs, but no effect on male longevity, sex ratio, and size of male nymphs. Lower developmental thresholds for each preimaginal stage and total development were approximately 10 degrees C. Upper developmental thresholds for eggs and first instars were approximately 30 degrees and 25 degrees C, respectively. There was no survival of eggs at 10 degrees C or crawlers at 32.2 degrees C. Net reproductive rates were 31, 49, and 8 viable females per female at 20, 25, and 30 degrees C, respectively Optimal temperature for development, survival, and reproduction, within the range examined, was 25 degrees C. Sex ratio was 1:1 at all three temperatures tested (20, 25, and 30 degrees C). Size of female third and fourth instars only were significantly affected by temperature.