Frequency-dependent food selection in locusts: a geometric analysis of the role of nutrient balancing

We used a geometric modelling approach to investigate how changes in the frequency in the environment of foods with different nutritional profiles affect the regulation of macronutrient (protein and digestible carbohydrate) intake and the pattern of food consumption of fifth-instar nymphs of Locusta migratoria (L.) (Orthoptera: Acrididae). Two experiments were conducted, both with insects individually housed in arenas containing four dishes of chemically defined synthetic food. In one experiment two nutritionally imbalanced, but complementary, foods (high;protein, low carbohydrate (P) and low protein, high carbohydrate (C)) were presented at different frequencies (4P:0C, 3P:1C, 2P:2C, 1P:3C and 0P:4C). The locusts regulated their feeding among the food dishes such that they defended their intake of both protein and carbohydrate, despite differences between treatments in the relative frequency of the two food types. In a second experiment, optimal (O) and suboptimal (either P or C) synthetic foods were paired in different relative frequencies. Despite the opportunity to ingest only optimal food, the locusts included suboptimal foods in their diet to varying degrees. However, they fed preferentially upon the. optimal food when it was presented along with dishes of suboptimal food and they increased their fidelity to dishes of the optimal food as they decreased in frequency relative to dishes of suboptimal food. Patterns of consumption in both experiments were consistent with the control of food choices and intake being governed by a combination of known mechanisms, including direct metabolic feedback and learning. (C) 2001 The Association for the Study of Animal Behaviour.