Background. Chayote is a popular vegetable in Reunion Island. Traditionally and extensively cultivated for its leaves, it is nowadays usually intensively cultivated under treillises for the production of fruit. A high number of fruit fallen on the ground result in a significant loss in production. Farmers attribute this to three fruit fly species (Bactrocera cucurbitae, Dacus ciliatus and Dacus demmerezi) which roost in the trellises. This situation provokes major insecticide applications in the chayote trellises to combat fruit flies. The present study aimed therefore at evaluating the real incidence of fruit flies in chayote cultivation. Methods. The experiments were conducted in 2008 and 2009 and observations in trellised crops were performed in different sites on the island. In 2008, hundreds of fruit were collected at a single site to study the susceptible stage of the chayote fruit while the development of samples of 20 recently blemished fruit and 20 unblemished fruit was regularly followed in the field. In addition, 120 blemished fruit were collected in 2008 in two sites 20 fruit were weekly collected at a site in 2009 and the emergence of adult flies was measured in the Cirad laboratory over 15 days. In addition, bird nets were placed under the trellis of three fields in 2009 to collect fallen fruit and the number of blemishes and the infestation of the fruit gathered were examined. In the lab, eight chayote fruit were exposed to gravid females per fly species and dissected. Results. In situ, fruit smaller than 6 cm length appeared to be unaffected by female blemishes. Two to four weeks after blemishes under the trellis, the blemished fruit did not show any morphological difference compared to unblemished fruit. This observation was strengthened by the results of emergence tests: only one of 120 blemished fruit collected in 2008 and only five fruit collected from 219 fruit harvested in the crop in 2009 showed emergence of flies. D. ciliatus appeared to be t