Abstract Larval critical weight, which is the threshold weight for a final-instar larva to initiate pupation, is not dependent on temperature. Three constant temperatures (25°, 20° and 15°C) were tested and had no singificant effect on the critical weight of final-instar larvae of Cnephasia jactatana. Latent feeding period, however, was prolonged from 3 days at 25°C temperature to about 9 days at 15°C. Larval maximal weight increased from 21.3 and 23.8% of the critical weight at 25°C, and 53.4 and 55.8% of the critical weight at 15°C for males and females, respectively. Since drop in weight from larval maximal weight to pupal weight and to adult weight were not affected by temperature, lowering the rearing temperature led to higher pupal and adult weights, probably due to an overall increase in feeding and assimilation during the latent feeding period. Females reared at 15°C were heavier and significantly more fecund than those reared at 20° or 25°C. Increasing the latent feeding period by using a low temperature is therefore important in improving reproductive performance and the overall quality of adult insects.