Mechanosensory pegs constitute stridulatory files in grasshoppers.

Stridulatory files on the inner face of hindleg femora were shown to consist of mechanosensory pegs in males and females of Syrbula montezuma (Saussure) and in males of Chorthippus biguttulus (L.). Females of Chorthippus had stiff protuberances on their stridulatory files, with an innervated tubercle instead of pegs. Pegs and tubercles of adult grasshoppers were shown to develop from innervated tubercular hairs present from the first instar onward in Chorthippus. In adults of Chorthippus, two sensory cells innervated each peg of males and each tubercle of females. Central projections of these afferents from the stridulatory files were very similar to those of the neighboring tactile hairs on the femur. The afferents from pegs in Syrbula responded to deflection and pressure introduced via the widened cuticular cap. In both species, selective stimulation of femoral cuticular receptors elicited antagonistic reflex responses in a coxal retractor muscle: pegs inhibited and neighboring hairs raised the efferent tonic discharges. Apparently, in these two distantly related grasshopper species, stridulatory files function as both sound-producing and proprioceptive organs.