Antennal sensilla of Magicicada cassini (fisher) (Homoptera : Cicadidae): Fine structure and electrophysiological evidence for olfaction

Abstract

The antennae of Magicicada cassini (Homoptera : Cicadidae) (3–4 mm long) look similar in both sexes and consist of scape, pedicel, and a 5-segmented flagellum. The length of flagellar segment 1 varies independently in relation to head size and is slightly longer in females (0.96 mm) than in males (0.89 mm). The ventral side of flagellar segment 1 is covered with sensilla coeloconica comprising about 60 large, 10 medium-sized, and 35 small sensilla with pit diameters of 8–24, 6–10, and 2 μm, respectively. The large and the medium-sized sensilla coeloconica are multiporous single-walled sensilla with pore tubules, containing branched entangled dendrites from 3 receptor cells. The small sensilla coeloconica, situated primarily at the outer border of the sensillum field, are no-pore sensilla with inflexible sockets. They contain 2 unbranched dendrites extending to the tip of the peg, and 1 dendrite reaching to its base and wrapping around the other 2 dendrites. Small sensilla campaniformia (cap diameter 3 μm) are aligned at the outer border of the sensillum field and continue all along the flagellum. Up to 3 olfactory receptor cells were distinguished on the basis of their nerve impulse amplitudes through extracellular electrophysiological recordings from sensilla coeloconica, presumably large ones. They respond to stimulation by cyclic terpenoids with different but highly overlapping reaction spectra, and react selectively to structural variations of the molecules. No responses to CO 2, temperature or moisture were recorded.