Ontogenese de certains aspects de l'orientation du grillon des bois Nemobius sylvestris (Bosc), dans son milieu naturel

Abstract

The ontogeny of the orientation of the wood-cricket, Nemobius sylvestris, was studied experimentally in a variety of biotopes. 1. 1) At a forest border, the insects of any age, when escaping, orientate towards 2. the outline of nearby trees. When these terrestrial cues are masked, each 3. newly hatched cricket exhibits an individual astronomical orientation which 4. progressively becomes common to the whole of the local population. 5. 2) Along a forest path, more crickets escape towards the trees at the sides 6. of the path as ontogeny progresses. They continually learn astronomical cues 7. which are the opposite to each other depending on whether the crickets live on 8. one edge of the path or the other. 9. 3) At a border of a sloping forest, the insects, during orientation, become 10. able to use gravity if visual (terrestrial and astronomical) cues are hidden. 11. 4) Within a dense forest a common direction of orientation was not observed. In each experimental situation, the straightness of the routes taken by crickets improves with age. These results demonstrate that, depending on the variety of the constraints within each living area, various local individual solutions to the problem of orientation develop during ontogeny.