The influence of wing length on mate preference was examined in natural populations of the Neotropical guava fruit fly, Anastrepha striata Schiner, at two locations in Costa Rica. Based on evidence that the fungi are transmitted during mating, site-specific infection by Laboulbeniales fungi on the body surface was used to assess mating history. Males and females that carried fungi on the legs and/or on the ventral part of the thorax (males), and on both sides of the notum and/or the dorsal base of the abdomen (females), had significantly longer wings than males and females without fungi. This suggests that individuals of both sexes with longer wings (i.e. larger individuals) enjoy higher mating success. Fungus infection is more frequent in the wet than in the seasonally dry forest, possibly because hosts are available year-round in the wet forest.