Carbohydrate-biased diets enhance marching behavior and lipid storage in juvenile locusts

Abstract Exceptional migratory capacity and voracious feeding make locusts a major threat to global food security. Although adult flight is known to be energetically demanding and fueled primarily by lipid reserves, the energetics of marching in juvenile locusts remain poorly understood. In many insects, terrestrial locomotion elevates metabolic rates by 2 to 12 times, potentially increasing the use and demand for carbohydrates and lipids. To investigate how marching interacts with dietary macronutrients, we examined fifth-instar nymphs of the Desert Locust (Schistocerca gregaria), one of the most destructive locust species across Africa and Asia. In the first experiment, nymphs marched for 5 h daily over 3 consecutive days. After each session, individuals were offered complementary pairs of artificial diets in a diet-choice treatment that allowed them to regulate protein-to-carbohydrate intake. Across marching and non-marching treatments, both groups consumed more carbohydrates than protein, indicating a carbohydrate-biased intake. However, marching individuals significantly increased carbohydrate consumption while maintaining protein intake comparable to control locusts. In the second experiment, locusts were assigned carbohydrate-biased, balanced, protein-biased, or diet-choice treatments throughout the final nymphal instar while marching daily. Consistent with the first experiment, marching locusts in the diet-choice treatment increased carbohydrate, but not protein, intake. Among the no-choice treatments, the carbohydrate-biased diet enhanced marching behavior, whereas the protein-biased diet reduced marching. Additionally, carbohydrate-rich diets increased body lipid content, while protein-rich diets increased lean mass in both marching and non-marching locusts. These findings demonstrate that carbohydrate-rich diets play a critical role in supporting marching behavior and migratory potential in locusts.