The selection of nutritionally balanced foods by Locusta migratoria: the interaction between food nutrients and added flavours

To investigate the ability of insects to discriminate between nutritionally balanced and unbalanced foods, fifth-instar nymphs of Locusta migratoria L. (Orthoptera: Acrididae) were given one of thirteen pairings of artificial foods differing only in their concentration of protein and carbohydrate. One food, containing a previously estimated optimum balance of these nutrients, was common to each pairing. The relative intake of this 'target' food increased on the more extreme pairings, i.e. the insects demonstrated increasingly strong preference for the balanced food when it was paired with unbalanced alternative foods. When distinctive non-nutritional flavours (tannic acid and amygdalin) were added to one or both of the foods, the insects' intake of the unbalanced foods increased, particularly on high-protein foods. It is suggested that learned associations were not involved in the observed patterns of selection and that the added flavours disrupted the chemosensory responses to nutrients used by the insects to differentiate foods in this context.