A study of mitosis in the brain cells, size of nuclei of the median neurosecretory cells of the brain, dry weight, and accumulation of glycogen and trehalose during the 4th larval stage of the black salt-marsh mosquito, A. taeniorhynchus (Wiedemann), under the conditions where pupal ecdysis is manifested as a diurnal rhythm with more than 3 peaks, showed diurnal rhythmic patterns in mitosis in brain cells, size of nuclei in the median neurosecretory cells, and amounts of available trehalose in the body. Dry weight and glycogen did not show any diurnal rhythmicity even with different quantities of food provided to 4th-stage larvae. Higher quantities of food than basic ration synchronized larval development as well as pupal ecdysis, thus only 1 major peak of mitosis in brain cells was exhibited, and trehalose diurnal rhythmicity was suppressed. A light regime did not show phase-shift of the diurnal rhythm of trehalose. Maximum amounts of trehalose with indications of diurnal rhythmicity were expressed under 12 hours light: 12 hours dark as compared with con tinuous light or continuous dark, at 32°C. It is suggested that diurnal rhythmic patterns investigated here in the larvae endure to the pupal stage with the occurrence of pupal ecdysis as a diurnal rhythm.