Extensive field observations were undertaken to study the population dynamics of the larvae ofCatopsilia crocale in the Madurai Kamaraj University campus during the years 1980–81 and 1981–82. Though oligophagous,C. crocale adopted ‘monophagic strategy’ for oviposition and larval feeding. Seasonal changes in the nitrogen content of the foodCassia alata leaf influenced the pupal/adult weight and oviposition. Commencement of rain triggered the reproductive activity and continued precipitation facilitated maximum egg deposition. Of total egg production in a year, about 80% was oviposited during northeast monsoon (September–December) and the rest during the south-west monsoon (May–August). Egg, I instar, V instar and pupa suffered more mortality than the other life stages. Of the total number of eggs laid, about 1·01% emerged as adult and 98·99% died during the process of larval and pupal development.