Adult and larval population fluctuation of the South American fruit flyAnastrepha fraterculus(Wiedemann) (Diptera: Tephritidae) has been determined and related to host availability. A peak in the adult population on each host occurred five weeks after the peak in larval population. The average number of larvae per fruit is between 1–5 in large hosts (guava, peach and loquat) and it is smaller than one for small fruit (surinam cherry).