Ultraviolet-deficient greenhouse environment affects whitefly attraction and flight-behavior

The effect of a UV-deficient environment on the attraction and dispel sal b ehavior of whiteflies, Bemisia argentifolii (Bellows & Perring), and on the transmission efficiency of die whitefly-borne tomato yellow leaf curl gemi nivirus, was tested under field conditions and through controlled experimen ts. We found that the late of tomato yellow leaf cull virus-disease spread to tomato plants grown under walk-in tunnels covered with regular greenhous e plastic sheets increases sharply with time, whereas the virus infection-r ate under UV-absorbing sheets proceeds at a very slow pace. Average number of whiteflies trapped under regular plastic sheet tunnels was significantly higher than numbers trapped in UV-absorbing plastic sheet tunnels. Similar ly, the average number of whiteflies trapped on yellow-sticky traps placed on the outside walls of tunnels covered with regular plastic was higher tha n the number trapped on the outside walls of tunnels covered with UV-absorb ing plastic sheets. No differences were found in the whitefly's ability to transmit tomato yellow leaf curl virus under the two types of plastic cover s. Whitefly dispersal pattern under the two types of plastic covers was exa mined using a release-recapture experiment. In each type of walk-in tunnel we established a grid of yellow-sticky traps forming two concentric circles : an inner and an external. Under UV-absorbing tunnels, significantly highe r numbers of whiteflies were captured on the internal circle of traps than the external circle, The fraction of whiteflies that were captured on the e xternal circle was much higher under regular covers, when compared with UV- absorbing covers, suggesting that filtration of UV light hindered the abili ty of whiteflies to disperse inside these plastic tunnels. Our results indi cate that the mechanisms by which UV-deficiency protects covered crops from insect infestation and spread of viruses are that the lack of UV interfere s with insect flight orientation; and that the lack of UV radiation alters the normal behavior of the invading insects, resulting in reduced dispersal activity.