Since 1999, Tomato Yellow leaf curl virus and Tomato yellow leaf curl Sardinia virus (genus Begomovirus, family Gemoniviridae) are severely infecting tomato crops in Southern Morocco in the region of Agadir. Economic losses ranged between 20 and 100%. High populations of Bemisia tabaci, the vector of these viruses, were observed on tomato, other crops and weeds. In spite of careful physical and chemical protection of the crops against the whiteflies, TYLCV remains a problem in tomato production suggesting that the TYLCV inoculum pressure is high. Thus, flight activities and infectivity of natural populations of B. tabaci were monitored during the tomato growing season in 2002 and 2003.