Introduction. Fruit fly attack on citrus causes economic yield losses in Nigeria. The high demand for sweet oranges in recent times necessitates the need to develop control strategies that can reduce fruit fly damage and ameliorate yield. This can be achieved by identifying the diversity, abundance and spread of major sweet orange fruit flies. Materials and methods. Surveys were conducted during the citrus fruit maturity periods of 2003 and 2006 in citrus-producing areas of Nigeria. Owners of the sampled orchards were interviewed on their cultural practices that could contribute to fruit fly abundance and spread. The fruit flies were sampled by using two types of trap; namely, the McPhail® trap with yeast hydrolysate bait and the yellow sticky trap impregnated with ammonium acetate. The traps were hung on the citrus trees at a distance of 1.8 m from the ground. The distance between trees was 25 m and the traps were replicated three times per site. Results and discussion. Fruit flies identified on citrus belonged to the genera Bactrocera, Ceratitis, Dacus and Trirhithrum. While higher fruit fly diversity was observed in Edo, Ogun and Oyo states in the rainforest ecological zone, relatively higher populations of major genera (Bactrocera and Ceratitis) were recorded in Benue and Kaduna states in the Guinea savanna ecological zone. Bactrocera species occurrence increased during the second sampling period. Some farmers’ cultural practices were implicated as factors likely to have contributed to fruit fly abundance and spread. Conclusion. Fruit fly species of economic importance to citrus in Nigeria belonged to the genera Ceratitis and Bactrocera species. These genera were observed in the majority of surveyed areas.