A dermal light sense influencing skeletal structure in locusts

Abstract

Evidence is presented for a long-term metabolic dermal light reaction in two species of adult locusts, Schistocerca gregaria and Locusta migratoria. Chitin lamellogenesis in the hind tibial endocuticle, normally coupled to a circadian clock, can be uncoupled in a graded manner by constant light at constant temperature during cuticle deposition. The lower the light intensity, the slower is the uncoupling (e.g. 6 days at 0·1 ft-c.; 1 day at 75 ft-c.). Uncoupling by constant light still occurs after ablation of both compound eyes and all three ocelli. Locusts can detect light with some agency other than the eyes. The site of light reception is not the living food-plant. Uncoupling by light can still occur in endocuticle growing in a cylinder of hind tibia which has been implanted loose in the haemocoel, but it does not occur in an effectively painted leg. This would appear to eliminate the involvement of the central nervous system or endocrine system. The response appears to be local, probably in each epidermal cell, and as such is probably a dermal light sense, sensu stricto. An equal energy action spectrum analysis shows that the dermal light sense in Schistocerca has a threshold between 0·1 and 0·5 ft-c. at the peak of its action spectrum, which lies between 435 and 520 mμ.