Spermidine alleviates heat shock and promotes the growth of Bombyx mori

Silkworms have limited ability to regulate their body temperature upon exposure to varying atmospheric temperatures. Environmental changes, such as global warming, adversely affect silkworm viability. Spermidine, a polyamine, protects various organisms against heat stress. This study aimed to evaluate the effect of spermidine on the thermotolerance of Bombyx mori larvae. 5th instar Bombyx mori larvae were divided into the control and spermidine groups and reared at 28 ± 1 °C and 80%-85% relative humidity. To induce heat stress, the larvae were exposed to various temperatures 32 °C, 36 °C, and 40 °C for 1 h on day 5 and subsequently allowed to recover at 28 ± 1 °C. Growth characteristics were evaluated by examining larval viability and quantifying proteins and carbohydrates. The thermotolerance of the spermidine group was higher than that of the control group at 40 °C heat stress conditions. The spermidine feeding increased the protein content and reduced the carbohydrate content significantly under heat stress condition. For the first time, this study demonstrated that spermidine alleviated thermal stress by enhancing the nutritional indices and antioxidant potential of the Bombyx mori larvae. A significant increase in economic properties was observed in spermidine fed groups. Thus, foliar feeding of spermidine to B. mori larvae markedly improved silkworm thermotolerance.