Plasticity in food preference and diet-induced differential weighting of chemosensory information in larval Manduca sexta

The complement of chemosensory organs required for food discrimination was examined using larvae whose food preferences were differentially affected by rearing on either the host plant, Lycopersicon esculentum, or the acceptable non-host plant, Vigna sinensis. Larvae having different types of chemosensory organs remaining after microsurgery were given a choice between leaf discs of V. sinensis and wetted filter paper discs (water). Information mediated by the lateral maxillary sensilla styloconica is necessary to detect the feeding deterrent properties of V. sinensis by larvae reared on L. esculentum. In contrast, larvae reared on V. sinensis are stimulated to eat this plant, which requires inputs from both the antennae and the maxillary palps. Although the remaining chemosensory organs also mediate food selection, their contribution to a normal level of food selection could not be demonstrated. Thus, feeding responses to V. sinensis require information from only a subset of the available chemosensory organs. This need varies with the dietary experience of the larvae. The same subset is required to mediate a diet-induced food preference when larvae are given a choice between L. esculentum and V. sinensis. These results show for the first time that the antennae and the maxillary palps can be more important in mediating food selection by M. sexta larvae than the maxillary sensilla styloconica and the epipharyngeal sensilla. The dominance of certain chemosensory organs over others in mediating food selection suggests perception of stimuli carrying weighting factors of substantially different strength. The switch in feeding response to V. sinensis from deterrent (by larvae reared on L. esculentum) to stimulatory (by larvae reared on V. sinensis) seems to be due to changes in weighting factors assigned to stimuli detected by (1) the antennae (increase) and (2) the maxillary palps (increase) and/or the lateral maxillary sensilla styloconica (decrease). The results do not support linear processing of chemosensory inputs underlying feeding responses to V. sinensis.