In order to better control fruit flies (Diptera: Tephritidae) attacking Cucurbitaceae on Reunion Island (21°6 S/ 55°36 E), biological characteristics (seasonal fluctuation, relative abundance, sex ratio) of communities roosting in corn borders were investigated. The study was conducted in austral summer across a range of altitudes (750–1150 m) corresponding to the main areas of cucurbit cropping. Living adults were recorded roosting on corn planted within or around cucurbit fields. Results showed a high variability in seasonal fluctuation of populations according to local conditions. Bactrocera Cucurbitae (Coquillett) (Diptera: Tephritidae) was the least abundant species (27%) compared to Dacus ciliatus Loew (36%) and Dacus demmerezi Bezzi (37%). Relative abundance of B. Cucurbitae was lowest (< 18%) in high altitude sites (above 1000 m), where D. demmerezi was the most prevalent species (> 56%). Dacus ciliatus showed variable relative abundance (from 18 to 51%) depending on the experimental design (varying in location and in year). Sex ratio was also very variable from one species to another and from one experimental design to another.