抄録
Silkworm (Bombyx mori) larvae showed both negative geo-orientation and positive photo-orientation at the termination of their cocoon constructions. Only a few moths were able to escape from the cocoons if the prepupae assuming ordinary "head-up" posture were inverted in the cocoons. The gravitational response was predominant when a light was present near the lower end of vertically-set cocoons. Illumination at the upper end increased the frequency of larvae assuming the final head-up posture in cocoons when the long-axes formed angles between 0-15 degrees from horizontal. The threshold value evoking the photo-orientation response was between 2-20 lux. Vitamin A-deficient and while-eye larvae of an ommochrome-deficient mutant failed to show the photo-orientation. Experiments in which larvae were coated with paint revealed that one particular posterior ocellus located on both sides functions to receive light in the photoresponse. The functional significance of the orientations in the silkworms is discussed.
