The antennal movement apparatus in the small tortoiseshell (Aglais urticae L., Insecta, Lepidoptera)

Abstract

1. The club-shaped antenna ofAglais urticae L. consists of 34–37 segments (scape, pedicel, and flagellar segments; Fig. 1) covered by hairs and scales (Fig. 4a). Only the scape and the pedicel can be moved by muscles (Fig. 6). 2. The head-scape joint may be compared to a ball-and-socket joint. The scape can be moved in various directions by four muscles of the head (Fig. 6a). The scape-pedicel joint functions like a hinge joint, about which axis G3-G4 the pedicel together with the flagellum can be turned upwards by one muscle and downwards by two muscles of the scape (Figs. 6b and 7). This axis, when the antenna is in resting position, makes an angle of ca. 40° (pointing forwards) with the longitudinal body axis when projected into the horizontal plane (Fig. 14). 3. The pedicel-flagellum joint, as all the successive joints, is of almost radial symmetry (Fig. 2). The flagellar segments can only be moved passively by a relatively small amount. 4. Aglais has in its pedicel a highly developed Johnston's organ (Figs. 8–10), the sense cells of which can probably perceive passive movements of the flagellum in relation to the pedicel. The active movements of the antenna can be controlled by Bohm's bristles on the scape and the pedicel (Figs. 3–7). 5. The Johnston's organ, the Bohm's bristles and the antennal muscles are supplied by nerves which arise in the deutocerebrum (Figs. 11 and 12). 6. During flight the antennae are stretched forward almost horizontally (Fig. 1). The adjustment of this antennal flight position is discussed (Figs. 13 and 14).