Diseases vectored by whiteflies : etiology, ecology, geographical distribution and possible control measures

The whitefly-transmittcd viruses produce a wide and divergent group of diseases, most of which have not been characterized. The agents are transmitted by at least three whitefly species in the nonpersistent, semipersistent, persistent and by biological mechanisms. The viruses cause significant losses throughout the world and are responsible for some 70 important diseases in the tropical and sub tropical areas. Recent years have shown an increase in losses in wide areas north and south of the tropics, approaching areas of intensive agricultural production. The whitefly-transmitted diseases have been characterized in general on the basis of their transmission by whiteflies and the activity of the agents on host plants, such as symptoms and host range. A compilation of available data on the viruses themselves would suggest at least seven groups of viruses differing in type of virus particle, symptom type, and vector relationships. The two major groups of whitefly-transmitted viruses of worldwide importance (the geminiviruses and closteroviruscs) are differently transmitted by biotypes of Bemisia. This vector specificity impacts virus distribution and epidemiology. Transmission systems may be valuable to trace origins of viruses and their vectors.