AGE-RELATED RESPONSES FROM THE MAXILLARY SENSILLA STYLOCONICA OF CHORISTONEURA-FUMIFERANA LARVAE TO FOLIAGE EXTRACTS FROM BALSAM FIR HOSTS

An electrophysiological study of the sensilla styloconica of the galea in Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae) larvae s howed a differential response between fourth- and sixth-instars to ext racts of balsam fir foliage. Larvae raised on artificial diet were sti mulated with the water soluble fraction of needle extracts obtained fr om terminal and lateral shoots of 30- and 70-yr-old balsam fir trees. An extract-sensitive neuron was found in the lateral styloconic sensil lum of both instars. The lateral styloconica in the fourth-instar larv ae were more sensitive to extracts from terminal than from lateral sho ot foliage of both young and old trees. The lateral styloconica of six th-instar larvae were more sensitive to lateral shoot foliage of old t rees. Results are discussed with respect to their relationship to feed ing preferences and feeding rates observed in a previous behavioural s tudy.