The expression of locomotor circadian rhythm in female German cockroach, Blattella germanica (L.).

Fifteen percent of intact female German cockroaches (n = 13), Blattella germanica (L.) (Dictyoptera: Blattellidae), had weak free-running locomotor rhythmicity under 28 degrees C and constant darkness conditions. However, 86% of ovariectomized females (n = 14) showed a strong free-running rhythm under the same conditions with a circadian period of 23.60 +/- 0.15 h, similar to the male's period of 23.45 +/- 0.03 h. In addition, the locomotory activities occurred mainly during the subjective night under DD conditions as was the case in males. These results indicated that female locomotion was under the control of a circadian oscillator, which was masked by the existence of ovaries. This internal masking effect could be removed by the existence of males, but females had no effect on the locomotor pattern of another female. Since the male failed to entrain female locomotion, its role as a zeitgeber was excluded. That the locomotory pattern of the females still coincided with their reproductive cycle when exposed to male odor suggests that exposure to a male only partially removed the internal masking effects.