DissertationAccessibility to safe, nutritious and healthy fruits and vegetables is essential for maintaining an active life and critical for the survival of all people. The demand for high quality fruits and vegetables has been growing considerably in developing countries for the past few years. Such higher demand has created a new lucrative trade opportunity for fruits and vegetables. In addition to increased liberal trade arrangements and people movement between countries, the international trade of fruit and vegetables has resulted into introduction of exotic plant pests of quarantine importance including fruit flies (Diptera: Tephritidae) in partner countries. Apart from the devastating damages caused by indigenous fruit flies, exotic fruit flies have also been causing tremendous loss in fruits and vegetables including cucurbit crops. Previous studies indicated that cucurbit infesters vary in their diversity, infestation rates and distribution with geographical location and season. Presence of fruit flies in Morogoro region was initially reported by Mwatawala et al. (2006). However, the ecological structure (diversity, species composition and abundance) as well as host preference of cucurbit infesters in Tanzania remained largely unknown. A thoroughly understanding of ecological structures and host preference of fruit flies is a prerequisite if sustainable management programmes is to be formulated and deployed. Therefore, this study assessed the diversity and host preferences as well as spatial and temporal abundance of fruit flies infesting cucurbit crops in the Morogoro region. Experiments were laid out in a full factorial design. Factors were seasons, agroecological zones, tapping weeks and fly species. Trapping of fruit flies was conducted from March to November 2020 in ten established cucurbit fields focusing on cucurbit infesting flies. Tephri traps were baited with one of three different baits: Cue-Lure (CL), BioLure (BL) and Zingerone (ZN) to attract members of the genus Dacus and Zeugodacus. On other hand, a minimum of 10 fruits were also randomly collected from each plot during the peak of fruiting season followed the methodology described by Copeland et al. (2002). Fruits were transported to the rearing facility in the horticulture unit at Sokoine University of Agriculture (SUA) Morogoro. Emerged adults were removed and handled following methods described by White and Elson Harris (1994). In total, 21 673 fruit fly specimens were collected and 22 146 flies emerged from reared fruits. The trapped specimens belonged to 19 species from three genera (Dacus, Zeugodacus and Bactrocera). Of the total specimens collected, Zeugodacus cucurbitae was the most dominant species and accounted for 83.4% of the total specimens collected. All of the remaining species constituted the remaining 16.6% of the total specimens. Results also showed significant differences in infestation rates among Zeugodacus cucurbitae (Coquillet), Dacus vertebratus Bezzi and Dacus ciliatus L. (P<0.05). The effects of host, altitude, season and fruit fly interactions on infestation rates were also significant (P<0.05). Cucurbita maxima was the most preferred host by Z. cucurbitae at all altitudes, C. lanatus was preferred host for D. vertebratus and C. maxima was the preferred host for D. ciliatus L. Incidence of Z. cucurbitae showed significant association with host crops (P<0.05). On other hand incidence of D. vertebratus showed significant association between host and altitude (P<0.05). Likewise, D. ciliatus incidence showed significant association between host, altitude and season (0.05). The results from this study suggests that among the fruit fly species, Zeugodacus cucurbitae, D. bivittatus, D. punctatifrons, D. vertebratus, D. ciliatus, D. telfaireae and B. dorsalis represented the most devastating group of cucurbit infesters. Therefore, we recommend that, any management program should focus to suppress their population by considering the agroecological zones, crop phenology and growing season.Belgian Directorate General for Development Co-operation (DGDC),Sokoine University of Agriculture (SUA),Eduardo Mandlane University (EMU),Royal Museum for Central Africa (RMCA)-Belgium.