response to optical cue during pre-oviposition stage and oviposition response to lightness of the water surface IDOMAL:0002329 IDOMAL:0002329 Light contrast and dark contrast may both have different causes. The apparent lightness of a body of water may be due to reflection from a pale substratum or to specular reflection from the water surface. A body of water may appear dark relative to its surroundings due to high absorbance by the water or its substratum or to a shielding from incident light. Observing that when kept in complete darkness in a roomsized cage females of Culex quinquefasciatus laid in the oviposition dishes provided (dishes which had chemical cues), whereas females of Anopheles darlingi died without ovipositing. De Zalueta (1950) postulated that visual stimuli were essential for egg laying by Andarlingi but not for Culex quinquefasiatus, for which chemical stimuli were more important. idomal_namespace