Spectral sensitivity in insect photoreceptors at a range of temperatures

The function of the visual receptors of blowflies (Calliphora erythrocephala) was studied using intracellular recording techniques where by the eye was kept at various temperatures below room temperature. Cooling was found to reduce the response amplitude, decrease the time course, and increase the latency. The Q10 as calculated from different recordings and from various temperature steps was found to be dependent both on the temperature range and the stimulation intensity, although more on the latter. From different kinds of spectral sensitivities of the receptor cells those with a double peak (UV and green) were studied with regard to the effect of the temperature change. We found a difference in the relative sensitivity change of the two peaks if the temperature was lowered. The sensitivity in UV remained enhanced in relation to green after cooling. This finding can be considered as supporting the sensitizing pigment theory, according to which the double peaked spectral sensitivity is explained by assuming a photostable pigment transferring the energy to the photopigment. This support is valid if the UV sensitivity at room temperature is assumed to be higher, and is limited by the reduced energy transfer to the photopigment caused by the increased mobility of the sensitizing pigment.