Orientation of the cricket Nemobius sylvestris (BOSC) towards forest-trees. Daily variations and ontogenetic development
Résumé
One-year-old nymphs of the wood cricket Nemobius sylvestris released in an open ground, for instance in the middle of a forest path, orientate their escape towards the outlines of the nearby tree trunks. This orientation reaction fluctuates during daytime, being lowest around 15.00 hours. Furthermore the majority of the insects returned to the trees located on the same side of the path where they were captured. During ontogenesis, this orientation behaviour can be divided into several characteristic stages. At first, 0 to 2 week-old nymphs are able to orientate towards black targets but not towards trees. Three-week-old nymphs can orientate towards the trees, but the preferential escape direction towards the dwelling area only appears at 6 weeks. It is suggested that with successive associations signal-reinforcement occurs during ontogenesis, firstly with tree-trunks, secondly with an astronomical direction.