Introduction. Host preference of Zeugodacus cucurbitae in three vegetables was determined under choice and no-choice experiments. Materials and methods. The experiments were conducted in both semi-natural (under cage) and natural (no cage) field conditions. The trials were run for three seasons between March 2013 and July 2014 in Morogoro Region, Tanzania. In each season, two sets of plots of watermelon Citrullus lanatus, cucumber Cucumis sativus and pumpkin Cucurbita sp., were established in mono and mixed cropping systems. A set of plots was placed under individual cages and another set of plots was left open. Colonies of Z. cucurbitae were regularly established from wild cucurbits and the emerging adults were maintained on artificial diets. The adults were released into cages once in a cropping season, at a sex ratio ratio of 1:1. A total of 60 and 180 adults were released into choice (4 × 4 m) and no choice (4 × 12 m) plots respectively. Open fields were infested naturally. Released adults were between 21 and 30 days old post emergence. Flies were released between six and eight weeks after sowing the vegetables. Fruits were harvested a week after release of flies into cages. Trials were also conducted to determine the dominant cucurbit infester in cucumber. Infestation rates and incidences were determined and used to indicate preference of Z. cucurbitae among the three vegetables. Results and discussion. Highest infestation rate of Z. cucurbitae was recorded in watermelon while lowest in pumpkin. Infestation rates were significantly high in fruits grown under no choice compared to choice plots. More flies emerged from fruits grown in no choice plots. However, infestation rates were not significantly different among fruits from natural and semi-natural conditions. Other cucurbit infesters, Dacus bivittatus, D. frontalis, D. vertebratus and D. ciliatus emerged from fruits grown in open (no cage) field plots. Further results show that Z. cucurbitae dominated Dacus bivittatus and D. frontalis in cucumber. Conclusion. Watermelon is the most preferred host of the dominant cucurbit infester Z. cucurbitae.