Adult population fluctuations of wildAnastrephafruit flies were determined by McPhail trap captures in 5 orchards of different fruit species at the Soconusco region in Chiapas, Mexico. The main fruit fly hosts at these orchards were orange, guava (low and highlands), sapodilla,Achras zapotaL., and chalum,Inga michelianaHarms. All plant species exhibited different fruiting phenologies. Fruit fly species composition varied among the orchards with 1 or 2 predominant species representing from 43 to 86% of theAnastrephaindividuals. The predominant species were always associated with the main fruit host in the orchard. Adult populations varied strongly between and within orchards. In all cases, peak population numbers of predominant species were recorded shortly after the period of maximum host fruit availability. Simple regression analysis between fly numbers and rainfall showed that this environmental factor cannot explain population fluctuations, whereas host fruit availability can be considered the most important environmental factor affecting adult populations in these tropical orchard habitats.