The intluence of wing length on mate preference was exanúned in natural populations of the Neotropical guaya fruit tly, 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. At both.sites, males and females that carrled fungi on the legs andlor on the ventral part of the thorax (males), and on both sides of the notum andlor 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-roimd in the wet forest.Se estudió poblaciones naturales de la mosca frutera Anastrepha striata Schiner, en dos lugares de Costa Rica. Los hongos Laboulbeniales se transmiten en éstas durante la cópula. Hembras y machos con hongos en las patas y/o parte ventral del tórax (machos), y en ambos lados del noto y/o base dorsal del abdomen (hembras), teRÍan alas significativamente más largas que los individuos no parasitados. Esto sugiere que los individuos más grandes logran más apareamientos.