Evidence for the role of retinal receptors R 7/8 in the orientation behaviour of the fly

The height orientation of flying houseflies Musca domestica has been analyzed:

1. The luminance threshold of the orientation behaviour has been determined. It corresponds to the luminance threshold needed for the optomotor response in the torque released by the receptors R 7/8 (Eckert, 1973).
2. The direction of the E-vector of the linearly polarized stimulating light has been varied at a luminance just above threshold. It was found that the ability of the fly to fixate is dependent upon this parameter.
3. The rhabdomeres R 1–6 and/or 7/8 have been stimulated selectively and the threshold of the height orientation response has been measured under the different conditions of stimulation. It has been found that the threshold of luminance, when all receptors are stimulated, is almost identical to the threshold when only the receptors R 7/8 are stimulated. If the receptors R 1–6 are stimulated specifically the response threshold is rised by 1 to 2 decades of illuminance, as compared to the specific stimulation of R 7/8.

It is concluded that the results of all experiments are in accordance with the hypothesis, that the receptors R 7/8 are necessary for the orientation behaviour.