Taste cell responses in the polyphagous arctiid, Grammia geneura: towards a general pattern for caterpillars

The caterpillars of Graminia geneura are polyphagous as individuals. Electr ophysiological responses of its medial and lateral galeal styloconic sensil la to 21 amino acids, 6 carbohydrates, 10 chemically diverse plant secondar y compounds and two inorganic salts were examined. In the medial sensillum, a single cell responded to 8 amino acids, 3 carbohydrates, and the iridoid , catalpol, which is present in a favored hostplant. In the lateral sensill um, one cell responded to amino acids and another to fructose. Two cells in each sensillum responded to secondary compounds and it is suggested that t he same cells are stimulated by inorganic salts. There was no evidence of a separate salt-sensitive cell. Phenylalanine stimulated a deterrent cell in the medial sensillum and was behaviorally deterrent. Some essential amino acids did not stimulate any cells and it is suggested that a small number o f amino acids (sometimes non-essential) may serve as indicators of nutrient quality. Sugars probably serve as the primary phagostimulants because they are in relatively high concentrations in plants. It is proposed that taste receptor cells should be categorized primarily by their behavioral effects as phagostimulatory or deterrent, rather than their specific ranges of res ponsiveness. This would emphasize the basic similarities across taxa. (C) 2 001 Elsevier Science Ltd. All rights reserved.