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Abstract Mythimna separata (Walker) is a destructive grain crop pest in China and other Asian countries. However, the effects of fluctuating environmental conditions on M. separata populations remain poorly understood. Here, we investigated how fluctuating temperatures affect the development, reproduction, flight capacity and energy reserves of both migrant and resident populations of M. separata . Our experiments demonstrated that fluctuating temperatures (20–30°C) significantly accelerated development but inhibited adult reproduction and reduced triglyceride reserves in both migrant and resident populations compared with a constant temperature of 25°C, because the larval period, pupal period, lifetime fecundity, mating frequency, ovarian development and triglyceride content significantly decreased, while the preoviposition period obviously increased. A relative decreased tendency of flight capacity was observed for migrants and residents under fluctuating temperatures. We also confirmed that populations and sexes differed in their responses to temperature variations. Mythimna separata residents showed slower development, weaker flight capacity and lower triglyceride content but greater reproductive performance than the migrants under both fluctuating and constant temperatures. Furthermore, female migrants had greater flight potential and triglyceride levels than those of males at both constant temperature and fluctuating temperatures. These findings expand our knowledge of the relationships between fluctuating temperatures and armyworm development, reproduction, energy reserves and adaptive strategies in a complex ambient environment.
Lv et al. (Fri,) studied this question.