Transgenerational effects of thermal stress on reproductive physiology of fall armyworm, Spodoptera frugiperda

Temperature is one of the critical abiotic factors influencing the range, richness, activity, life history and viability of insects. The persistence trend of thermal stress on biological and reproductive traits were studied for invasive fall armyworm, Spodoptera frugiperda (J. E. Smith) by exposing early fourth instar larvae to thermal stress treatments (42° and 45 °C) for single and multiple times along with control (27 °C) and reared them till F 2 generation. Survival of larvae was minimum in 45 °C single (88%) and multiple thermal stress (92.5%). The carry over effect of thermal stress was evident up to F 2 generation for developmental attributes with prolonged developmental duration, reduced maturation success and female biased sex ratio. Reproductive parameters such as gonadosomatic index, eupyrene sperm count, fecundity and mating frequency reduced drastically as a result of thermal stress in F 0 generation and the effect persisted up to F 2 generation on fecundity and gonadosomatic index. The biochemical response due to thermal stress was investigated by analyzing metabolic reserves in the adult stage. The reduction in water content and accumulation of total sugar, glycogen, lipid and protein content was observed in adults of all three generations. A trade-off between reproduction and survival strategies was evident under thermal stress with the allocation of resources between them. Thus, our study provides a basic understanding on persistence of thermal stress across generations both at biological and biochemical level and offers insights into further studies on demography of fall armyworm under current and future climate change scenario.