The visual response from the compound eye of Oncopeltus fasciatus: Effects of temperature and sensory adaptation

Abstract

The effects of temperature (10–30°C) on response latency and amplitude were determined in the dark- and light-adapted compound eye of the milkweed bug, Oncopeltus fasciatus. Response amplitude was an inverse function of temperature under dark-adapted conditions, but was nearly independent of temperature when superimposed on a background field. Response amplitude to a test stimulus (S 2) was maximum at 15–20°C when presented 10 sec after an adapting stimulus (S 1). The optimum temperature (10°C or less) for maximum response amplitude from dark-adapted eyes was far below the temperature at which the animals were grown (19–25°C) and lower than previously reported for insect compound eyes. These results are discussed in terms of the adaptive implications for diurnal, terrestrial ectotherms. Response latency from dark-adapted eyes was an inverse exponential function of temperature with an apparent activation energy of 13·6 kcal mole −1. No change in activation energy could be attributed to light adaptation. Reductions of S 2 response latency and amplitude, during the adaptation régimes employed in this study, were different functions of temperature. Adapting stimuli, which were equally effective at reducing S 2 latency, had different effects on S 2 response amplitude. Recovery of S 2 response latency and amplitude were not related at either 20 or 10°C. Therefore, changes in S 2 response latency as a function of adaptation appeared independent of changes in S 2 response amplitude.