Aedes triseriatus oviposition in standard, horizontally open (open top) ovitraps was compared with that in vertically open (open-sided) ovitraps during 1989 in a deciduous woodland in southern Illinois. This comparison was to determine whether female oviposition preference changed as a result of seasonal photoperiod changes. Results show that Ae. triseriatus females prefer horizontally open ovitraps regardless of whether they are depositing eggs which hatch shortly after deposition or whether the eggs diapause because of shortened late summer/early fall photoperiods.