Effects of short- and long-term thermal stress on developmental stages and adults vis-à-vis reproductive physiology of Spodoptera litura

Abstract Temperature is a critical environmental factor influencing insect development, physiology, and distribution. Global warming is predicted to increase the frequency and severity of extreme heat events, influencing insects differently across life stages. This study investigates the effects of short- and long-term thermal stress on the tobacco cutworm, Spodoptera litura , a polyphagous pest damaging over 389 plant species. We exposed eggs, larvae, pupae, and adults to elevated temperatures of 42°C and 46°C for four hours and one hour, respectively, in single and repeated occasions for two, four, two and two days for egg, larva, pupa and adults, respectively. Our results demonstrate significant variation in biological and reproductive fitness parameters across treatments. Notably, thermal stress skewed the sex ratio towards females. We also observed impacts on offspring survival and potential negative carry-over effects. Overall, the effects of heat stress were dependent on temperature, exposure duration, and life stage, with adults exhibiting the highest tolerance. These findings suggest that S. litura possesses a degree of heat tolerance that may enable it to survive summer heat waves, but its offspring and other life stages could be more vulnerable under future climate scenarios.