Invasions by exotic species in areas already occupied by related species may lead to extinction or niche partitioning. Bactrocera dorsalis has invaded the Comoros archipelago in 2005 where other tephritids were already present. The host ranges of fruit flies in the Comoros were studied by conducting a seven-year survey on the three islands of the archipelago with a substantial sampling effort comprising 91 plant species from 37 families. The results showed that 45 fruit species in 16 families were infested by tephritid species. Eight fruit fly species were detected in the sampled fruits, but 78% of the individuals were identified as B. dorsalis, confirming its dominance and polyphagous status. More than ten years after its invasion, B. dorsalis has replaced Ceratitis capitata as the dominant fruit fly species on several species such as mango and citrus. The coexistence between B. dorsalis and C. capitata seems possible due to the capacity of the latter to exploit different niches, i.e. higher altitudinal ranges and a few host fruit species (among which, chillies and coffee berries) constituting a refuge niche. Information about coexistence between B. dorsalis and other tephritids is useful for the management and better estimates of invasion risks and associated biosecurity measures.