The Spectral Sensitivity and the Components of the Visual System in the Stemmata of Silkworm Larvae, Bombyx mori L. (Lepidoptera : Bombycidae)

Abstract

The electroretinograms (ERGs) of the stemmata of silkworm larvae were recorded with the active electrode on the proximally blocked ocellar nerve and the reference electrode in the abdomen. From the responses to various intensities of monochromatic lights of wavelength 340 to 638 mμ, response-log relative intensity curves were obtained. These curves are not parallel among different wavelengths. These curves were used to construct the spectral sensitivity curve by deducing the relative number of quanta required to evoke a constant response. The spectral sensitivity curves showed one peak in the near ultraviolet and another hump or peak in the blue-green or green region of the spectrum. The latter peak was more prominent at lower intensities than at higher ones. Monochromatic light adaptation selectively influenced the relative spectral sensitivity and the form of the ERGs, suggesting that two receptor systems (UV and G) exist in the silkworm stemmata, which differ in spectral sensitivity and which may mediate true color vision. As a clue to find the spectral sensitivities of the individual receptor systems, color specific difference in the latency of the ERGs was utiliized. Two hypothetical spectral sensitivity curves thus obtained considerably overlapped and that of the G-receptor system showed a peak at about 540 mμ. However, no exact position of the maximum sensitivity of the UV-receptor system could be illustrated.