Heliothis armigera Hubner is a serious pest of sorghum earhead. Studies to determine the rate of multiplication of its population were conducted at 26 ± 1°C temperature and 75% relative humidity. Under a given set of conditions and food supply its population on sorghum earhead increased with an infinitesimal and finite rate. The population multiplied 285·06 times between two successive generations and one generation was completed within 46·71 days. The population on reaching the stable age-distribution comprised approximately 99% of immature stages.