Electrophysiological responses to sucrose from a gustatory sensillum on the larval maxillary palp of the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae).

The tip of the maxillary palp in the spruce budworm and other lepidoptera larvae contains a cluster of eight basiconic sensilla. Except for a few electrophysiological recordings from the entire group of these sensilla, no information is available on the response characteristics of any individual one. Using a compound microscope at 320x magnification, with a long working-distance objective, it has been possible to view individual sensilla and to record electrical responses from three of these to some gustatory stimuli in preliminary tests. One of them, sensillum (L1), contains a sugar-sensitive neuron whose responses to a range of sucrose concentrations are reported here. The physiological characteristics of this neuron differ from those of the known sugar-sensitive neuron in the lateral styloconic sensillum on the galea of these same insects. Input of chemosensory information about the same gustatory stimulus by more than one neuron in different mouthpart sensilla is discussed in relation to the feeding habits of the spruce budworm.