Effects of naturally varying temperatures on growth and development and nutritional indicators of Mythimna separata (Walker) (Lepidoptera: Noctuidae)

Mythimna separata is a major migratory agricultural pest in China, with its number of generations varying significantly along latitudinal gradients, posing a serious threat to grain production and security. To address the current lack of fundamental temperature-response data for predicting outbreaks in third-generation occurrence areas, this study systematically investigated the developmental characteristics of this pest under naturally fluctuating temperature conditions. Three complete generations were observed during the April-October 2021 study period, with each generation’s developmental progression showing a significant correlation with temperature variations. The second generation developed fastest during the high-temperature period in July, completing its life cycle in only 48.2 d. When the temperature reached approximately 25 °C, the developmental duration shortened significantly, but the larval survival rate decreased. Fifth-instar larvae exhibited the strongest environmental adaptability, with starvation tolerance lasting up to 281.4 h. This study provides guidelines for predicting M. separata occurrence in third-generation breeding areas under natural conditions.