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A comparison of nutritional regulation in solitarious- and gregarious-phase nymphs of the desert locust Schistocerca gregaria

S. J. Simpson^*, D. Raubenheimer, S. T. Behmer, A. Whitworth and G. A. Wright

Department of Zoology and University Museum of Natural History, University of Oxford, South Parks Road, Oxford OX1 3PS, UK

View larger version (23K): [in a new window]   Fig. 1. Protein–carbohydrate intake arrays for solitarious (A) and gregarious (B) desert locust nymphs. Filled symbols represent intake points for locusts provided with a single food, whose protein and digestible carbohydrate content is indicated at the end of each dotted line (%protein:%carbohydrate). Open symbols show the mean intake points for locusts provided with a choice of either food 28:14 with food 14:28, or food 14:7 with food 14:28. Values are means ± S.E.M. (N=7–20). Intake did not differ between these latter two treatments, indicating regulation of protein–carbohydrate intake. This selected point of intake (‘intake target’, labelled IT) provides a reference for interpreting the intake array across the no-choice treatments (see Fig. 2). The data indicate cumulative intake from ecdysis (day 0) until day 3 (squares), day 5 (triangles), day 8 (inverted triangles), and across the entire stadium until adult ecdysis (circles).

View larger version (20K): [in a new window]   Fig. 2. Graphs plotting the relationship between over-eating one nutrient (protein, P, or carbohydrate, C) and under-eating the other versus food composition, relative to the selected point of intake when insects were provided with a choice of complementary foods (the intake target, IT, from Fig. 1). Data are for intake up to day 5 in the stadium. The theoretical minimum nutritional error (absolute sum of over-eating one nutrient and under-eating the other relative to the intake target) is shown as a dotted line. Note how solitarious insects (A) followed a strategy that minimised the total nutritional error, while gregarious locusts (B) tolerated over-eating the nutrient in excess relative to the intake target (hatched region).

View larger version (28K): [in a new window]   Fig. 3. Protein–carbohydrate intake array for one-generation solitary-reared desert locust nymphs. Refer to Fig. 1 for explanation. Values are means ± S.E.M. (N=9–10). ITg and ITsol indicate the self-selected protein–carbohydrate ratios for gregarious and three-generation solitarious nymphs, respectively (from Fig. 1). Data indicate cumulative intake from ecdysis (day 0) until day 3 (squares), day 5 (triangles), day 8 (inverted triangles), and across the entire stadium until adult ecdysis (circles).

View larger version (16K): [in a new window]   Fig. 4. Utilisation plots for protein growth across the entire fifth stadium versus total protein intake (A) and for lipid growth versus total digestible carbohydrate intake (B). Circles are for solitarious locusts and squares are for gregarious insects. Values are means ± S.E.M. (N=7–20). The points from left to right along each curve in the protein utilisation plot are for foods 7:35, 14:28, 21:21, 28:14 and 35:7; for the lipid utilisation plot, the order is 35:7, 28:14, 21:21, 14:28 and 7:35 (see Materials and methods). Triangular symbols indicate the points achieved by insects provided with a choice of complementary foods and, thus, able to reach their intake target. Triangles are for solitarious insects and inverted triangles for gregarious locusts.

View larger version (37K): [in a new window]   Fig. 5. Graphs showing development time (A) and percentage survivorship (B) across the fifth stadium for solitarious (open columns) and gregarious (hatched columns) locusts confined to foods containing a fixed proportion of protein (P) and digestible carbohydrate (C) (diet treatment labelled as %P:%C). Values are means + S.E.M. (N=7–20 in A, 12–20 in B).