Determination of Thermal Constant and Development Threshold of Pink Borer, Sesamia inferens

Effect of constant temperatures viz., 18±1, 21±1, 24±1, 27±1, 30±1 and 33±1°C was studied on the egg, larval and pupal development of Sesamia inferens. Development rate of egg, larva and pupa gradually increased with increase in temperature, while total developmental period decreased. Mean developmental period of the pest decreased from 116.6 days at 18±1°C to 31.8 at 33±1°C. The lowest and the highest temperatures at which no development took place were found to be 9±1ºC and 39±1°C, respectively. Regression equations between development rate and temperature were found to be Y= 0.021X-0.290 (R²=0.94) for egg; Y= 0.002X-0.020 (R²=0.92) for small larva (1^st-3^rd instar); Y=0.005X-0.056 (R²=0.76) for large larva (4^th-5^th instar) and Y=0.006X-0.076 (R²=0.89) for pupa, respectively. Thermal constant for egg, small larva, large larva and pupa was determined as 47.6, 500.0, 200.0 and 166.7degree days (DD), respectively with corresponding development threshold being 13.8, 10.0,11.2 and 12.7°C. Thermal constant to complete a generation was found to be 874.3 DD.