Spatial orientation in the bushcricket Leptophyes punctatissima (Phaneropterinae; Orthoptera): I. Phonotaxis to elevated and depressed sound sources.

Many species of acoustically interacting insects live in a complex, arboreal or semi-arboreal habitat. Thus mate finding by phonotaxis requires sound localization in the horizontal and vertical plane. Here we investigated the ability of the duetting bushcricket Leptophyes punctatissima to orient to one of three speakers, positioned at different levels in an artificial grid system, where each point in space could be reached by the male with almost equal probability. The system was designed analogous to a spherical calotte model of bismuth, where, once the male arrived at any nodal point had to decide between only three directions: either up or down and/or left and right. This design does not favour any phonotactic path of the males. All 12 males tested reached the three speaker positions (one in the horizontal plane, one elevated by 45 degrees , one depressed by 45 degrees relative to the starting position) with only little deviation from the shortest possible path. There was no significant difference with respect to the whole phonotactic time needed, the number of segments passed, or the number of stimuli received for the different speaker positions. This remarkable spatial orientation is achieved although the insects have no specialized external ear structures such as mammals, or some owls.