Effect of Temperature and Relative Humidity on Different Life Stages of Spirama retorta Cram. (Lepidoptera : Noctuidae)

Temperature and humidity are the two main factors that influence the rate of survival, oviposition, growth and development and the fecundity of an insect. Experiments were carried out during 1996-97 to determine the effect of temperature and relative humidity on the egg, larval, pre-pupal and pupal period of Albizia foliage feeder, Spirama retorta Cram. (Lepidoptera:Noctuidae), a devastating pest of forest nurseries and young plantations in Central India. The recorded field temperature during study/survey period was 5 to 45°C and relative humidity 20 to 80% in Central India covering the state of Madhya Pradesh, Maharashtra and Orissa. Study of the effect of temperature and humidity revealed that the best suited optimum temperature and relative humidity was between 30-35°C and 60-80% which enhanced the viability of eggs and shortened the egg, larval, pre-pupal and pupal duration. Low temperature (5 - 25°C) and humidity (20 - 60%) lessened the viability of eggs and increased the mortality and the duration of various life stages. The maximum mean viability of eggs (99.00 ± 1.00) was recorded at 30°C and 80% where as the shortest egg period was 3- 4 days observed at 35°C and 40-80% relative humidity. The shortest mean period in days was also observed for larval (11.12 ± 0.3750), prepupal (1.62 ± 0.1250) and pupal (9.67 ± 0.2870) between 30 - 35¤C and 60-80%. These finding were correlated with the field temperature and humidity and found that temperature, humidity and species of food plants (quantitative and qualitative) favored this insect to occur in an epidemic condition, in forest nurseries and young plantations during monsoon season.