EFFECTS OF TOTAL LIGHT DEPRIVATION ON VISUALLY GUIDED ORIENTATION OF THE FIELD CRICKET GRYLLUS-BIMACULATUS

Visually guided orientation is studied during ontogeny in field crickets (Gryllus bimaculatus) bred into complete darkness from egg stage. It is compared to control animals bred in normal 12L/12D light cycle conditions. Control animals are strongly scototactic: whatever their age, 85% of them step towards low reflecting targets. On the contrary, for the experimental group (visually deprived), only 20% of the first larval instar crickets orientate towards vertical black stripes on a white background. A frame by frame analysis of video recordings allows to measure more accurate parameters of the orientation trails. Results show that experimental animals, already at the fifth larval instar, are able to orientate towards the targets as many as the control ones, nevertheless, they still present strong, permanent impairments of exploratory behaviour and visual fixation.