The Role of Weed Hosts and Tobacco Thrips, Frankliniella fusca, in the Epidemiology of Tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) and other closely related tospoviruses are serious threats to many agricultural, ornamental, and greenhouse crops. TSWV was first recorded in the southeastern United States during the middle to late 1980s (10,12,16,19,23), with the first collections of the western flower thrips, Frankliniella occidentalis (Pergande), following shortly thereafter. In North Carolina, TSWV was first detected in tobacco and tomato in 1988, although infections occurred at very low levels. During the following 6 to 8 years, TSWV incidence remained low and was widely scattered among fields, suggesting that endemic inoculum sources had not yet become established. By 1997, TSWV had occurred in nearly every North Carolina county, with the incidence in some individual fields reaching high levels. Since then, many flue-cured tobacco fields have experienced 30 to 50% losses, and county-wide incidence of infected plants has averaged 10 to 15% in Duplin, Onslow, and Pender counties. Although area-wide levels of infection were lower in 2000, some tomato, pepper, and tobacco fields again experienced 25 to 50% infected plants. Worldwide, this virus is transmitted by at least eight thrips species (8,26). In eastern and central North Carolina, the primary vector of TSWV is the tobacco thrips, Frankliniella fusca (Hinds), although F. occidentalis may be locally important, especially in the western Piedmont and mountainous portions of the state (12). Thrips acquire TSWV by feeding on infected plants as larvae, with a subsequent latent period of approximately 3 to 7 days before transmission of the virus to uninfected plants (36), and remain competent vectors for the remainder of their lives. Thus, only those plants that sustain virus infections and serve as suitable reproductive hosts for the vector can be considered important sources for spread of TSWV. TSWV has an extensive host range including over 600 plant species (2,3,7,8,20– 22,24,28,31). Many plants susceptible to TSWV do not support thrips reproduction and are considered a “dead end” for virus spread (11). A more complete understanding of the sources of vector reproduction and TSWV infection is warranted to determine which plant species may serve as both reproductive hosts for vectors and the primary inoculum sources for TSWV spread. The current study was conducted to systematically identify, through field collections, wild plant species supporting both vector reproduction and natural TSWV infection in North Carolina.