CEREBRAL EXTRAOCULAR PHOTORECEPTORS IN BEETLES

Cell clusters containing rhabdomeric structures and screening pigments are located in the optic lobes of pupae and adult beetles of Tenebrio molitor and Hylotrupes bajulus. Due to their resemblance with the com pound eyes, the cell clusters were called cerebral extraocular photore ceptors (CEPs) and can readily be detected macroscopically as black sp ots spread between the lamina and medulla. CEPs of T. molitor responde d to bright light with a transient depolarisation followed by a sustai ned plateau. In contrast, CEPs of H. bajulus responded to bright light either with small depolarisations or did not respond to the range of light intensities presented. CEP cells labelled with Lucifer yellow ha d axons projecting toward the medullar region. The maximum spectral se nsitivity of CEPs was broadly tuned to the green region (lambda(max) a t 524 nm). The role of CEPs in insects is still a matter of wide specu lation, due to the lack of consistent systematic behavioral studies ab out insects carrying photoreactive CEPs. Here we suggest that the scat tered distribution of CEPs in the optic lobes could allow a temporal F ooling of information about the surrounding illumination, thereby entr aining some rhythmic photobehavioural responses. (C) 1997 Elsevier Sci ence Inc.