Ovipositing butterflies use a red receptor to see green

Swallowtail butterflies of the species Papilio aegeus oviposit on the leaves of Rutaceae plants in Australia. They possess receptor types with sensitivity peaks around 390 nm (violet receptor) and 610 nm (red receptor), in addition to the receptor types common in insects with sensitivity peaks at 360 nm (ultraviolet receptor), 440 nm (blue receptor) and 540 nm (green receptor). Multiple- and dual-choice experiments show that females of P. aegeus prefer to oviposit on substrata that look green to humans. A class of simple models is developed to describe this choice behaviour in terms of linear interactions between the different spectral types of photoreceptors. The green receptor has a positive influence, whereas the blue (and possibly the ultraviolet and violet) receptor and the red receptor have negative influences on the choice behaviour. Colour choice for oviposition is thus guided by a single chromatic mechanism. Caterpillars of P. aegeus grow faster on young leaves which, according to the model, should be preferred by females for oviposition. The importance of the red receptor for the discrimination between different green leaves is discussed in ecological and comparative contexts. Finally, in an evolutionary perspective, the possibility is discussed that colour vision systems like those of honeybees might have evolved as a combination of two or more such chromatic mechanisms.

Electrophysiological Properties of R7 and R8 in Dipteran Retina

Intracellular recording and dye injection have directly demonstrated the absolute and spectral sensitivities of R7 and R8 in the eye of Calliphora. R8 has major peak of sensitivity at 547 nm with less than half the bandwidth of a theoretical rhodopsin, and a subsidiary peak at 358 nm. R7 is confirmed as being an ultraviolet receptor. Both have absolute sensitivities similar to those of R 1 -6. These results are inconsistent with the scotopic (R1-6), photopic (R7 and R8) theory of fly vision.

The Nature of the Retinal Action Potential, and the Spectral Sensitivities of Ultraviolet and Green Receptor Systems of the Compound Eye of the Worker Honeybee

1. The retinal action potential consists principally of a sustained negative wave which persists for as long as the stimulus. Transitory negative on-effects and off-effects may also be present, particularly at long wave lengths (green, yellow, and red) and in the light-adapted eye. 2. Only the maintained component of the potential can be elicited under CO2 anesthesia. The transient components are reversibly eliminated from the response at about the same time as the background noise of nerve and muscle spikes. It is suggested that the sustained component arises from the receptor cells, and the other components from second and higher order neurons. 3. The compound eye does not contain a homogeneous population of receptors. A green receptor system (maximum sensitivity at about 535 mµ) determines the response of the dark-adapted eye throughout most of the spectrum; during adaptation to yellow light, however, an ultraviolet receptor system is revealed, with maximum sensitivity at about 345 mµ. The anatomical bases of these receptor systems are unknown; however, they include both retinula cells and neurons in the optic ganglion. 4. There is no change in spectral sensitivity (Purkinje shift) in the first three logarithmic units above the threshold of the retinal action potential. 5. The relatively great effectiveness of near ultraviolet light in stimulating the positive phototaxis of the bee does not depend on excitation of the ultraviolet receptor of the ocellus.