Development and emergence patterns of the tobacco cutworm Spodoptera litura (Lepidoptera: Noctuidae)

Study of lifecycle patterns and rhythms is important to understand the ecology and evolution of insects. The tobacco cutworm Spodoptera litura (Lepidoptera: Noctuidae), is a serious polyphagous pest in Asia, Oceania and the Indian subcontinent. The laboratory investigations of development patterns and circadian rhythms described in this paper have shown that the development duration from egg to pupae is 21.5 ± 0.7 d in which the pupation peak took place in the 21st day after eggs being laid. The development duration from egg to adult is 33.0 ± 0.8 d and 35.0 ± 0.7 d for female and male moths, respectively. Adult emergence showed a circadian rhythm in both sexes where adults start to emerge in the afternoon and increased quickly and peaked at dusk and then declined gradually in a few hours into the night. The present study suggests that S. litura is a protogynous species. Protogyny may be a mechanism that has evolved to reduce inbreeding because early emerged females are less likely to mate with their brothers. In S. litura, eggs are laid in clusters with a cluster contain 50-300 eggs, from which inbreeding risks are increased due to offspring live together with high population density. Therefore, females emerge earlier than males should be extremely important in S. litura, and inbreeding avoidance should be the main forth behind the evolution of protogyny in this insect. Keywords— The tobacco cutworm; Spodoptera litura; Emergence; Larval development; Circadian rhythms