A number of observations on the population dynamics ofAnastrepha obliquaassociated with a mango plantation in Orotina, Costa Rica were carried out. (a) After eleven months sampling with McPhail traps, 54.63% of adults captured wereA. serpentina41.73%A. obliqua3.56%A. striataand 0.08%A. balloui.The period of maximum abundance of these species coincides with the fruiting season of the respective host plants,A. serpentinacoincided with the fruiting of several Sapotaceae,A. obliquawith some Anacardiaceae andA. striatawith some Myrtaceae. However all adults from infested mangoes wereA. obliqua.(b) The phenology of adult emergence ofA. obliquafrom the ground was observed in 1986. Most emerge just after the first rains; this coincides with the fruiting season, and emergence continues many weeks after the crop is over. (c) To determine the dispersal ofA. obliqua633 young adults were marked and released in the mango plot. Only one marked adult was recaptured five weeks later. Adults showed a tendency to disperse from the original plot.