Associative learning by locusts: pairing of visual cues with consumption of protein and carbohydrate

We investigated whether fifth instar African migratory locusts, Locusta migratoria, could learn to associate visual cues with the macronutrient content of synthetic foods. During a 48-h training period, the insects had ad libitum access to two synthetic foods which were identical in all respects except that one lacked protein and the other lacked digestible carbohydrate. One food was placed at the end of a transparent Perspex cylinder which had been tinted green, and the other at the end of a yellow-tinted cylinder which was similar in all other respects. To obtain a balanced diet, the insects were thus forced to ingest the two macronutrients in visually different environments. Following this training period, they were then made selectively deficient in either protein or carbohydrate, before being tested for their tendency to enter, and the depth of entry into, yellow-or green-tinted cylinders that did not contain food. Locusts entered significantly more frequently the colour of cylinder that had previously been paired with the deficient nutrient (henceforth termed the 'training colour'). This was true irrespective of whether the nutrient was protein or carbohydrate, and whether the training colour was green or yellow. There was no effect of training on the average depth of entry into the cylinders. However, protein-deprived locusts penetrated significantly more deeply than carbohydrate-deprived locusts into both green and yellow cylinders, irrespective of the training colour. A separate experiment demonstrated that naive locusts entered more frequently into the yellow than the green side-arm, but there was no influence of colour on the depth of entry by naive locusts. (C) 1997 The Association for the Study of Animal Behaviour.