Abstract

Electrophysiological responses from various chemosensilla on the maxillae of second instar spruce budworm larvae were obtained using sucrose and 1-amino acids as stimuli. Complementary tests stimulating the L1 on the maxillary palp and the lateral styloconic sensilla (LST) on the galea of fourth instars were also performed. The results from both second and fourth instars were then compared with earlier electrophysiological work done on older sixth instars. Sensitivity of responses from the sugar-sensitive cell of the L1 and the LST to sucrose for second, fourth and sixth instars revealed that the mean firing frequency of this cell remains unchanged in the L1 sensillum during larval development. However, for the LST an age-related sensitivity to sucrose was noted with increases in larval age. The LST and the L2 sensilla of second instars were stimulated with thirteen amino acids; however, only three (l-leucine, l-aspartic acid and l-valine) evoked a response in the former sensillum. No responses were obtained from the L2 sensillum to any of the amino acids, confirming that this sensillum does not possess an amino-acid sensitive cell, but instead has a water-sensitive cell, which is inhibited by higher concentrations of KCl. Further analysis of responses from the 1-proline-sensitive cell of the medial styloconic sensillum (MST) revealed that the second instar larvae are less sensitive to stimulations with 1-proline than are fourth and sixth instars. These results are discussed in relation to the changes in feeding preferences of larvae as they age