The disease known as "spotted wilt" was first described in Australia in 1 9 1 5 ( 16) and shown to have a viral etiology b y Samuel et al i n 1930 ( 14 1 ). Since that time, viruses similar or identical to the tomato spotted wilt virus (TSWV) have been the cause of plant diseases epidemics in tropical, subtropical, and temperate regions throughout the Northern hemisphere, Western Europe, and Asia (2, 7, 19 , 29, 30, 55, 56, 78, 80, 105 , 108, 1 5 1 , 1 53 , 170). Major economic losses are due in large part to an extremely wide host range involving more than 500 species of plants in more than 50 families that