Changes in taste receptor cell sensitivity in a polyphagous caterpillar reflect carbohydrate but not protein imbalance.

Caterpillars of the polyphagous arctiid, Grammia geneura, have a single cell in the medial galeal sensillum that responds to some sugars and to some amino acids. After conditioning on artificial diet containing unbalanced amounts of carbohydrate and protein, the responses of this cell alter. After protein-biased food it increases slightly, but after carbohydrate-biased food it decreases. Responses to both sucrose and amino acids change in the same direction and the changes would not provide the information necessary to redress a shortage of protein. The lateral galeal sensillum contains one cell that responds to fructose and another responding to some amino acids. The responses of each of these cells in the lateral sensillum are not consistently affected by conditioning diets. After conditioning for 20 h on a protein- or carbohydrate-biased diet, the insects started to feed without delay if offered carbohydrate-biased diet, but only after a pause if given protein-biased diet. This occurred irrespective of the conditioning diet. The duration of the first feeding bout was also longer on carbohydrate-biased diet and the longest bouts followed protein-biased conditioning.