Electron microscopy of the contact chemoreceptors of the stable fly, Stomoxys calcitrans (Diptera: Muscidae).

Abstract

The contact chemoreceptors of the stable fly, Stomoxys calcitrans L., are situated on the tarsi and labellum. In all the types of contact chemoreceptors observed, the distal nerve fibers were enclosed within a cuticular sheath which extends from the vicinity of the neurons to the setal base. One distal fiber, postulated as a mechanosensory fiber, terminates at the base of the seta, while the remaining distal fibers enter the thick-walled lumen and pass distad to the papilla. All tarsal and labellar contact chemoreceptors examined show a pore in the papilla at the site of action, beneath which the distal nerve fibers seem to terminate unmodified. It appears, therefore, that the nerve fibers may be exposed to direct contact with chemical stimuli. The number of neurons associated with 2 types of tarsal contact chemoreceptors of Stomoxys is 5. Labellar contact chemoreceptors in the ventral rows and on the inner surface are innervated by 5, and 4 or 5 neurons, respectively. At the base of every tarsal and labellar contact chemoreceptor seta and tactile hair is a membrane surrounding the cuticular sheath which may function as a support for the cuticular sheath or aid in the detection of movements of the sensillum, or both.