The four mosquito species of insular Newfoundland were studied in terms of their seasonal succession and reproductive capacities . Fecundity was positively correlated with wing length in all species. The mean number of ovarioles per female was greatest in Aedes canadensis (173+48), followed by Ae. punctor (138+29), Ae. abserratus (121+27) and Ae. communis (107+36). Season-long sampling of the adult population levels and physiological age-grading suggested that no more than about 25% of adults (10% in Ae. abserratus) return for a second blood-meal and that <5% return for a third. The epidemiological significance of this to the transmission of California encephalitis viruses is discussed.