Odor of fermented yellow chapote (Sargentia greggiiS. Wats.) fruit was 3.6 times more attractive than yeast hydrolysate to hungry, laboratory-strain Mexican fruit flies,Anasttepha ludens(Loew), over short distances (<0.3 m) in laboratory experiments. Starvation for periods of 1–3 d increased responsiveness to chapote odor over the no-starvation level. Age had little effect on responses of flies between 1 and 30 dafter eclosion. However, newly emerged flies did not respond. Chapote odor attracted flies at all times during the 14-h photophase, but responses, especially of males, declined late in the photophase. Response levelsincreased with odor concentration throughout the range of test concentrations. Gamma irradiation reduced responses of females by 25% but did not affect responsesof males. Females were 1.7 times more responsive than males to chapote odor. Male-produced pheromone did not attract virgin females that were 0–7 d old (sexually immature) but attracted virgin females that were 8–37 d old (sexually mature). Odor of fermented chapote and maleproduced pheromone are maximally attractive to different segments of the adult population.