Proboscis extension in the blowfly: directional responses to stimulation of identified chemosensitive hairs

Abstract

We studied the direction of proboscis extension elicited by stimulating each of an identified array of gustatory sensilla, the ‘largest’ hairs, on the labellum of the flyPhormia regina. Individual hairs, or pairs of hairs, were stimulated with sucrose or water and the angle of the ensuing extension of the proboscis was recorded. The direction of the response was graded and depended on the identities of the hairs stimulated. Hairs situated on the anterior region of the labellum elicited anterior extensions, mid-level hairs elicited lateral extensions and posterior hairs resulted in posterior extensions. Previous studies of the labellar hairs have been concerned with their encoding of the chemical nature of the stimulus. Our findings show that each hair also relays information about the location of the stimulus. The positional information provided by these sensilla may help the fly to orient itself with respect to a food source.