Bemisia tabaci is among the most serious pest, causing worldwide economic losses, especially as vector of geminiviruses, including Tomato yellow leaf curl virus (TYLCV). Since 1997, TYLCV, has been responsible of great losses on tomato production in Reunion island. B. tabaci infestations were not observed in Reunion before the detection of TYLCV. The Reunion population of B. tabaci was analysed with silverleafing and transmission tests, PAPD-PCR analysis and sequencing of a Portion of a mitochondrial gene (COI). Alcohol preserved individuals from Madagascar Mauritius and Mayotte were characterised by the molecular techniques. Two groups of B. tabaci were genetically distinguished in Reunion. One, similar to biotype B, supposed to have been recently introduced into Reunion along with TYLCV, the other is distinct from any other genotype analysed so far, and is supposed to be native to the Mascarenes. To examine the possibility of genetic interchange between the B and the native genotype, microsatellite markers are being developed. A begomovirus was detected in leaf samples collected in Madagascar with TAS-ELISA and a PCR test using degenerate primers expected to amplify a region of the A component of begomoviruses. An expected size product of 500 bp was amplified, cloned and sequenced. Sequence comparisons showed a relatively high percentage of nucleotide heterogeneity between the begomovirus sequences of Madagascar ranging between 94 to 98%. The highest nucleoride identity was detected with Tobacco leaf curl virus from Zimbabwe (TbLCV) (77%), suggesting that the begomovirus from Madagascar belongs to a new species. (Texte intégral)