Identification of photoreceptor locations in the compound eye of Coccinella septempunctata Linnaeus (Coleoptera, Coccinellidae)

Abstract

Three spectral types of photoreceptor with sensitivity maxima in the 360 nm (u.v. light), 420 nm (blue light) and 520 nm (green light) were characterized in the compound eye of Coccinella septempunctata Linnaeus by intracellular electro-physiological recording. All three different spectral types of photoreceptor were found to respond to polarized light with an average polarization sensitivity (PS) value around 4.0. Referring the longitudinal direction ( Y-axis) of the compound eye as 0°, the e-vector of polarized light giving maximal sensitivity were 45° for the u.v. receptor, 75° for the blue receptor, 45 and 135° for the green receptor. These values were compared to the angles between the Y-axis of the compound eye and the microvillar directions in the rhabdomeres of eight retinula cells. It was concluded that all six peripheral retinula cells (Nos 1–6) were green receptors and that the two central retinula cells (Nos 7 and 8) were u.v. and blue receptors, respectively.