Some factors affecting the rate of dark adaptation in certain insects

Abstract

Mutant fruit-flies ( Drosophila melanogaster), which are rendered blind by intense light, gradually recover visual sensitivity to a test flash during dark adaptation—80 per cent recovery being achieved in some 30 to 60 sec. Changes in the time course of recovery and a refractory period, which may be considerable, occur with increasing duration or intensity of adaptation in a similar manner to that described for the chalky eyed mutant Calliphora which differs from the normal red eyed form only in the lack of screening eye-colour pigments. The mutant Drosophila has normal red eye colouration and is not simply excessively bleached by light as the Calliphora mutant. Wildtype Drosophila recover rapidly and abruptly in a similar manner to the hive-bee, 80 per cent recovery being achieved in 10 to 20 seconds or often less. It is suggested that processes limiting the rate of dark adaptation are common to the insects cited and the differences between the mutant and wildtype data indicate that the mutants lack certain parts of a common system. The present data add support to the theory of a dual visual system in the compound eye of Drosophila and suggest the mutant form described lacks a photopic mechanism.