EXPERIENCE-DEPENDENT CHANGES IN THE NUMBER OF CHEMOSENSORY SENSILLA ON THE MOUTHPARTS AND ANTENNAE OF LOCUSTA-MIGRATORIA

The effect of diet on the number of gustatory and olfactory sensilla w as investigated in locusts. Insects fed for the final two stadia on nu tritionally adequate synthetic foods have fewer sensilla on the maxill ary palps and antennae than insects fed on the usual rearing diet of s eedling wheat. This effect was seen irrespective of the nutritional ba lance of the foods and was independent of the concentration of nutrien ts present or the size of the insect. Supplying wheat odour to locusts fed synthetic foods had no effect on the number of sensilla present o n the palps, but completely reversed the decrease in the number of olf actory sensilla of the antennae and partially reversed the decrease in the number of antennal uniporous trichoid sensilla. Locusts that were allowed to select between two nutritionally unbalanced but complement ary synthetic foods had a higher number of sensilla on the maxillary p alps than those fed individual synthetic foods, providing the two food s differed substantially in their protein:carbohydrate ratios. Insects also developed more sensilla if they were fed on two foods of identic al nutritional composition but with different added flavours (1% tanni c acid or amygdalin). Exposing Locusts to synthetic foods for a single stadium did not cause any significant decrease in sensilla number. Th e results suggest that the number of sensilla that develop in a given sensory field is influenced by the variety of chemical stimuli experie nced and the chemical complexity of the environment as provided by the presence of distinct individual sources of stimulation.