Development ofPlatynota flavedanaClemens andP. idaeusalis(Walker) on a meridic diet was observed at constant temperatures in the laboratory. Lower developmental threshold values for egg, larval, and pupal stages ofP. flavedanawere 10.6, 8.6, and 9.0°C, respectively. Lower developmental threshold values of 9.7, 7.0, and 8.5°C were estimated for egg, larval, and pupal stages ofP. idaeusalis, respectively. Averages of 101.5 DD10.6, 379.6 DD8.6, and 126.0 DD9.0were required for development of egg, larval, and pupal stages ofP. flavedana, respectively.P. idaeusalisrequired 104.7 DD9.7442.7 DD7.0, and 132.2 DD8.5to complete development in the egg, larval, and pupal stages, respectively. Differences in rate of development were observed between food sources for both species.