Food mixing strategies in the desert locust: effects of phase, distance between foods, and food nutrient content
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abstract
Food mixing strategies were compared in the cryptically coloured, relatively sedentary 'solitarious' and the highly mobile, conspicuously coloured 'gregarious' phases of the desert locust, Schistocerca gregaria. Based on phase related differences in behaviour and nutritional regulatory responses, we predicted that solitarious nymphs, compared to gregarious nymphs, would move less between nutritionally complementary foods, particularly as the distance between the foods increased. We manipulated the nutritional composition [protein (p) and digestible carbohydrate (c) content] of two foods in an experimental arena and varied the distance between the foods using a factorial experimental design. Results indicated that in general, solitarious nymphs showed greater fidelity to individual food dishes than did gregarious insects (i.e., they concentrated their feeding mainly on one dish). However, results also demonstrated that for both phases fidelity to a particular food dish increased as the distance between the dishes increased, and that the number of switches between dishes decreased with increasing distance. In the smallest arenas, though, gregarious nymphs switched more frequently between the two food dishes than solitarious nymphs, even when the two dishes contained the same, near-optimal food (p18:c24). When challenged by having the two dishes either placed furthest apart (2 m) or more divergent in nutritional composition (p29:c13 vs. p7:c35), insects of both phases regulated protein intake more strongly than carbohydrate intake, by eating more from the dish containing higher-protein food.
