Ocelli, dark adaptation and landing reaction in a flesh fly (Calliphoridae)

Abstract

Previous researches have shown that in flies the landing reaction threshold is lower at lower light intensities. Since it is commonly observed that flies do not fly in darkness it has been hypothesized that the lowering of the landing reaction threshold may be due at least partly to a decrease in general activity mediated by the cervical ocelli (which are known to have a dynamogenic effect on other kinds of behaviour.

The experiments done to test this hypothesis have shown: 1) the landing reaction threshold is lower at low light intensities; 2) the adaptation process to light is slower than the adaptation to “darkness”; 3) the enhanced sensitivity to movement due to increasing darkness is not affected by the light falling on the ocelli; 4) the sensitivity to movement is affected not only by the illumination of the ommatidia stimulated by the moving stimuli but also by illuminating the ommatidia not directly stimulated by the moving stimuli.