Nine non-sprayed citrus groves located in the south of Tarragona and north of Castellón (Spain) were periodically monitored from 1992 to 1995 to determine the population dynamics of P. citri. Five male flights were detected, between April and November, and we observed significant differences in abundance between flights and years. The life cycle of P. citri is well-defined by the thermal parameters of 8.3°C as the lower developmental threshold and 562°DD (C) as the degree-days to complete a generation. Increases in female on trunk populations coincided with male flights. P. citri invaded the calyxes of newly settled fruits between May and July. By the end of this process, more than 70% of the calyxes were occupied by the insect. P. citri subsequently developed on the fruits, although in smaller percentages (20%). We observed increasing populations in the absence of natural enemies and decreasing populations of P. citri when natural enemies were present. Among the natural enemies, the coccinellidae predator, Cryptolaemus montrouzieri, stands out as well as several species of hymenopteran parasitoids.