The separation of nulliparous from parous Culex annulirostris using ovarian tracheation proved quick and reliable. Determination of physiological age, based on the number of ovariolar dilalations, proved slow but workable although some reservations remain regarding its validity. Abdominal pigmentation (similar to that seen in biting midges of the genus Culicoides), ovary color and consistency. body and wing wear, integumental color, presence of a meconium and presence of parasitic mites were generally of greater use than ovary size as indicators of parity. The physiological age of blood-seeking Cx. annulirostris, collected at Kowanyama (1540 specimens) and Charleville (1553) between 1974 and 1976, was determined by ovarian tracheation and ovariolar dilatation methods. Despite different climates, the seasonal age structures were similar at both localities, At Kowanyama and Charleville, 18.2% and 12,4%, respectively. were old enough to be capable of transmitting Murray Valley encephalitis virus. Gonactive pars and nullipars were collected throughout the year at both localities despite low winter temperatures at Charleville. The moderate longevity of Cx. annulirostris at Kowanyama (mean daily survival rate ± 1 standard deviation 72.1 + 10.1%) and Charleville (73.8 ± 11.7p) suggests that abundance may be a key factor contributing to the high vector potential of this species.