Abstract
In an artificial light cycle of LD 12:12, adult Rhodnius prolixus Stål, displayed a strictly nocturnal pattern of locomotory activity. Occlusion of the ocelli with black varnish did not affect the pattern; occlusion of the eyes or eyes and ocelli did not prevent entrainment to the LD cycle, but did affect the phase angle difference between the onset activity and the light to dark transition. It is concluded that this modified activity rhythm was synchronized via extracephalic photoreceptors.