Since 1998, Tomato yellow leaf curl virus was detected on tomato in Morocco. The virus was first detected near Casablanca and was later discovered in several regions particularly in the south near Agadir and in the north east near Berkane (DPVCTFR, personal communication). Economic losses ranged between 20 and 100%. In 1999, Tomato yellow leaf curl Sardinia virus was detected from Agadir. High populations of Bemisia tabaci, the vector of these viruses, were observed on tomato, other crops and weeds. Only biotype Q was identified in B. tabaci populations from Agadir. No sample were analysed so far from the north of the country. Since biotype B was reported from several Mediterranean countries, it was assumed that this cosmopolitan biotype could be present in Morocco. Therefore a survey of B. tabaci was undertaken in several regions to determine which are the biotypes present in Morocco and particularly in the north. Samples were collected from the north eastern Mediterranean coast (Saïdia, Berkane, Nador), from the north western region (Gharb region, Fez, Meknès) and from Agadir. Based on RAPID, cytochrome oxydase I gene sequencing and microsatellite markers biotype Q was detected in all the regions. Biotype B was only detected in the north eastern region. To our knowledge, this the first molecular detection of biotype B in Morocco. Following the severe outbreaks of tomato yellow leaf curl disease in tomato crops, several growers from Agadir developed techniques to reduce the impact of this new disease, particularly by the use of insect proof shelters. In spite of this careful physical control to prevent whiteflies to have access to the tomato plants, there are often a significant percentage of TYLCV infected plants. This suggests that TYLCV is efficiently transmitted by B. tabaci. To investigate this efficiency several experiments were carried out in a tomato farm in the region of Agadir. Natural populations of whiteflies have been trapped during a 3 month period. T