Within the genus Anastrepha, we find species that are key pests in fruit and vegetable crops and of quarantine importance for fruit importing countries. The knowledge of population fluctuation of these pests, in certain areas is a starting point for designing control strategies. The population fluctuation of fruit flies was evaluated in four localities of the Vinces canton, province of Los Ríos (La Americana, Santa Martha, Primavera and Pavana), using McPhail traps with hydrolyzed protein as bait. Three traps per site located on fruit fly host plants were checked weekly, in order to determine the fly.trap-1.day-1 (MTD) index and its correlation with climatic variables. The results show that the population peak is concentrated in December, with a MTD of 5.94, with a temperature of 27.40 °C and 78% relative humidity. A moderate positive correlation was found between the number of captured insects and the temperature expressed in °C, with a correlative value r2 = 0.61 and a negative correlation with relative humidity (r2 =-0.64). The most abundant species was Anastrepha fraterculus (Wiedemann) with 3,111 specimens, of which 1,055 were found in La Americana, the location with the highest infestation.