Mythimna separate's energy transformation was examined with reference to food consumption, the basis for tissue growth at various instars, assimilation rate, and respiration rate. According to experimental results based on live, dry body weight, a single Mythimna separata caterpillar's average daily consumption increased from the first to the sixth instar. More food was devoured by the male caterpillar than the female. Males' metabolic activity was shown to be higher during the I st , III rd , and VI th instar stages than they were during the II nd , IV th , and V th instar stages. Average values for tissue growth and respiration indicated that as tissue growth grew from the first to the last instar of the caterpillar, so did the average rate of respiration. The consumption of food that promotes the growth of insect pest tissue affects the metabolic rate of the larvae.