The control of antennae lift movements and its importance on the gravity reception in the walking blowfly,Calliphora erythrocephala

Abstract

1. Calliphora erythrocephala lifted its antennae during walking. On a horizontal walking plane the angleδ between the hind edge of the head and the longitudinal axis of the antennae amounts to nearly 20° in the walking fly and to 7° in the resting fly. The mobility of the joint between scapus and pedicellus is much higher than the mobility of the head-scapus-joint. 2. Immobilization or amputation of the antennae diminish the ability of the free walking fly for gravity reception (Figs. 2–4). A condition for gravity reception by the antennae is the mobility of the scapus-pedieellus-joint. The joint between head and scapus is unimportant in gravity reception (Fig. 5). The bristles inserted dorsally at the scapus (ScBo in Gewecke, 1967b) are involved in gravity reception. Elimination of these bristles causes an extension of the distribution of the walking directions if the mean walking direction of each single intact fly differs less than 10° from the negative geotactic basic direction (Table 2). 3. While fixed walking flies are rotated around their transversal axes, the positionδw of the antennae (δw = the angle between the hind edge of the head and the length axis of the antennae) depends on the inclination of the flies (Fig. 7). These angles vary between 12 and 20° in animals with immobilized head and between 15 and 24° in flies whose abdomens have been additionally immobilized. The position of the antennae loaded by a weight on the funicle is independent on the inclination of the flies during the rotation around their transversal axes.δloaded is great as the walking position of the unloaded antennae in flies walking horizontally. Cutting the bristles of the scapus which overtop the pedicellus (ScBo in Gewecke, 1967b) causes an increase of the amplitude of the lift-movement for all inclinations. But after this operation the position of the antennae is independent on the inclination of the fly's length axis (Fig. 9). There is also no correlation between the amplitude of the antennae lift-movement and the inclination if the fixed walking flies can only move their antennae in the joint between head and scapus (Fig. 10). This joint is therefore unimportant for the mechanism of gravity reception in fixed walking flies. 4. The lift-movements of the antennae are a condition for the mechanism of gravity reception in which antennal sense organs are involved. The scapus bristles are involved in this mechanism by limiting and determing the extent of the lift-movement. On contrast to the known principles of gravity reception in insects, an active movement of a part of the body (the antennae) is a condition for gravity reception in flies.