[Effect of the photoperiod of the site of oviposition of Aedes mariae (Diptera,Culicidae)].

The overwintering biology of Aedes (Ochlerotatus) mariae (one of the sibling species of the mariae complex) was studied in populations from the Tyrrhenian coast of Central Italy (Sperlonga and Formia). Ae. mariae has in this zone several generations per year and its larvae are commonly found from March to October exclusively in rock pools along the coast. Field and laboratory observations show in these populations an embryonic winter diapause induced by short-day photoperiods (9-12 hours). The photoperiod acts primarily on the parental females during their preimaginal life. The expression of diapause is influenced by temperatures and photoperiods experienced by the embryos. Full embryonic diapause is observed when the eggs are incubated at relatively low temperatures (less than 16 degrees C) and at short photoperiods. Short-day photoperiods also induce a remarkable change in the oviposition behavior of Ae. mariae. Laboratory observations show that the adult females readily oviposit on water surfaces when originating from larvae reared at long-day photoperiod while they are very reclutant to oviposit in the same situation when reared at short day photoperiod. Choice experiments involving four alternative oviposition sites (see Plate 1) demonstrate a preference for outside free water in long-day mosquitoes and for inside moist surfaces in short-day mosquitoes. The behavioral difference persists in successive gonotrophic cycles and it is not apparently affected by the photoperiod acting on the adult females. The above evidence together with recovery of overwintering eggs in holes and crevices of rock pools suggest that the shift in oviposition site shown in the laboratory reflects a similar shift occurring in nature. Such photoperiodically induced change in oviposition behavior seems to have an important adaptive significance in providing more constant microclimates to the diapausing eggs and in protecting them from the mechanical action of winter storms.