Evidence for the functional involvement of carotenoids in the photoperiodic reaction of spider mites.

Abstract

PHOTOPERIODISM in insects and mites depends on the presence of light-absorbing pigments, which are probably located in the central nervous system; photoperiodic responses are mediated by the direct action of light on these nervous elements1. Until now, pigments involved in photoperiodic processes such as diapause and polymorphism have not been identified. Different groups of pigments have been named by various authors as possible candidates for this function. A biologically active role based mainly on action spectra studies and the absorption characteristics of isolated pigments has been suggested for pterins2, carotenoids3, a combination of carotenoproteins, flavoproteins and haemoproteins4 and bile pigments5. Carotenoids, pterins and flavins have also been proposed as possible photoreceptor pigments in studies on the spectral sensitivity of circadian rhythms6. According to Lees1, however, the usefulness of action spectra in identifying the light acceptor is limited, as spectra for photoperiodic action cannot at present be matched against absorption curves. A different approach was used by Zimmerman and Goldsmith7, who reared Drosophila on a carotenoid-free diet and showed that in one generation the sensitivity of the visual receptors was lowered by 3 log units because of lack of rhodopsin. At the same time the photosensitivity of the rhythm of pupal eclosion in the cultures was not affected, from which it was concluded that the pigment involved in mediating light effects on the circadian rhythm in Drosophila is not a carotenoid derivative. We demonstrate here that carotenoids are functionally involved in the photoperiodic induction of diapause in the spider mite Tetranychus urticae using a method involving pigment mutants.