In recent years, the coconut whitefly, Aleurotrachelus atratus Hempel, has been recorded from various islands in the southwestern Indian Ocean. Field surveys in La Re´union, the Seychelles, the Comoros and glasshouses in Paris have allowed us to record this whitefly on 56 palm species, some of which are endemic and/or threatened species. Most of trees showed low infestation levels, except for the coconut palm that is its main host plant. Such a wide host range has facilitated the rapid geographical dissemination of this whitefly. A field study was conducted in 2006 in La Re´union, to gain a better understanding of the bioecology of A. atratus in a tropical insular ecosystem. The whitefly was found throughout the island, from sea level to 800-m altitude. Five parasitoid species (Hymenoptera: Aphelinidae) were found associated with the populations of this pest, with Eretmocerus cocois Delvare being the dominant one. A laboratory study showed that the pre-imaginal development of A. atratus is around 48 days at 25-27_C, which is relatively long compared to other whitefly species. With a sex ratio of one male per 1022 females collected in La Re´union, it appears that the whitefly reproduces by thelytoky. It represents a threat to ornamental and agricultural palms as well as to natural palm ecosystems in the absence of effective parasitoids.