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

We used a geometric modelling approach to investigate how changes in the fr equency in the environment of foods with different nutritional profiles aff ect the regulation of macronutrient (protein and digestible carbohydrate) i ntake and the pattern of food consumption of fifth-instar nymphs of Locusta migratoria (L.) (Orthoptera: Acrididae). Two experiments were conducted, b oth with insects individually housed in arenas containing four dishes of ch emically defined synthetic food. In one experiment two nutritionally imbala nced, 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 am ong the food dishes such that they defended their intake of both protein an d carbohydrate, despite differences between treatments in the relative freq uency of the two food types. In a second experiment, optimal (O) and subopt imal (either P or C) synthetic foods were paired in different relative freq uencies. Despite the opportunity to ingest only optimal food, the locusts i ncluded suboptimal foods in their diet to varying degrees. However, they fe d preferentially upon the. optimal food when it was presented along with di shes of suboptimal food and they increased their fidelity to dishes of the optimal food as they decreased in frequency relative to dishes of suboptima l food. Patterns of consumption in both experiments were consistent with th e control of food choices and intake being governed by a combination of kno wn mechanisms, including direct metabolic feedback and learning. (C) 2001 T he Association for the Study of Animal Behaviour.