Abstract

Gustatory responses to several sugars and l-amino acids in two age groups of Choristoneura fumiferana (Clem.) larvae were studied using electrophysiological methods. Sensitivity to the stimuli was assessed by stimulating the medial and lateral styloconic sensilla of the galea. Of the twelve common sugars tested on the lateral sensillum, fourth instars responded to melibiose, sucrose and raffinose. Sixth instars exhibited an order of sensitivity that was in accordance with earlier behavioural work on feeding responses; sucrose $>$ fructose $>$ m-inositol. A neuron in the lateral stylconic sensillum was found to be sensitive to all l-amino acids except l-proline. The latter was detected by a neuron on the medial sensillum. Sixth instar larvae were significantly more responsive to the l-amino acids than the younger instars. However, there was no correlation between the neurophysiological input measured in this study and behavioural output from a previous experiment with sixth instars. L-proline and l-valine proved to be the most stimulating, and dose-response curves for these two amino acids were plotted. Maximal responses for l-proline and l-valine were 50 mM/l and 1 mM/l, respectively. The threshold of the response for both compounds was lower than 0.001 mM/l.