Magnetic Orientation and Its Relation To Photic Orientation in Tenebrio Molitor L. (Coleoptera, Tenebrionidae)

Abstract

1. T. molitor is able to orient in a stimulus field without directional cues as provided by familiar stimuli like gravity and light. 2. The directional cue for such an orientation is provided by the earth's magnetic field because: a. rotation of the magnetic field causes rotation of the orientation direction; b. compensation of the field or its horizontal component results in a ran- dom distribution of the direction choices. 3. The magneto-menotaxis which the animals shows in a stimulus field with the earth's magnetic field as the only directional cue is traced back to the photic orienta- tion in the anisotropic light field the animals had been kept in during the pretesting period. If in the pretesting light field the dark direction1 shows an angular displace- ment in time, then the magneto-menotactic direction choice shows the same dis- placement. 4. Information storage about the spatial relations between the light and magnetic field seems to be a prerequisite for the transposition of photic into magnetic orienta- tion. The information stored seems to remain available for a fairly long period of time. 5. Experimental evidence indicates that T. molitor is able not only to determine the axial position of the horizontal component of the magnetic field (WILTSCHKO, 1972), but also its direction (North-South).