Flight activities of Bemisia tabaci in Southern Morocco and transmission of Tomato yellow leaf curl virus

Tomato yellow leaf curl virus and Tomato yellow leaf curl Sardinia virus (genus Begomovirus, family Geminiviridae) are infecting tomato crops in Southern Morocco in the region of Agadir with yield losses ranging between 20 and 100%. The severity of the infections has obliged the tomato growers to protect their crops from infestations of Bemisia tabaci, the vector of begomoviruses, using inseetproof screens. The aim of our study was to monitor the flight activities of B. tabaci over time at different heights and different directions (cylindrical yellow traps at 0.3 m, 1.30 m, 2.30 m, 3.30 m, 4.30 m high), and to assess their infectivity. Flight activities, recorded during 4 months in 2002 and 6 months in 2003 during the tomato growing season, were correlated with some weather factors. The ratio B. tabaci/ Trialeurodes vaporariorum was assessed on batches of tomato plants that were placed around the trapping mast and weekly changed. These plants were also used to monitor the infectivity of B. tabaci in relation to the flight activity. About 70% of the trapped whiteflies were collected from the lowest trap at 0.30 m. The number of whiteflies was decreasing with the increase of the height, the lowest yield was obtained with the two highest traps. The number of trapped whiteflies was positively correlated with temperature but negatively with wind. Relative humidity and rainfall (rare during experiments and more generally in the region of Agadir), could not be correlated to flight activities. Similar results were obtained in 2002 and 2003. In 2002, the insect monitoring was carried out with a trapping mast located beside tomato insectproof screenhouses. In 2003, the effect of the close environment on the flight activities was tested by comparing the results obtained with two masts, the one beside tomato insectproof screenhouses, and a new one about 500 m away within citrus orchards. At least 50% of the 24 susceptible tomato plants weekly exposed around the trapping mast were infected with TYLCV in 2002, indicating that among the trapped whiteflies there were always enough whiteflies that had access to virus sources, to infect a significant number of plants. As the large majority of the tomato crops are grown under insectproof screens in the region of Agadir, the availability of other potential TYLCV reservoirs has been investigated. (Texte intégral)