Entomologia Experimentalis etApplicata 78: 19-29, 1996. 19 9 1996 KluwerAcademic Publishers. Printedin Belgium. Variation in thrips species composition in field crops and implications for tomato spotted wilt epidemiology in North Carolina Craig S. Eckel 1, Kijong Cho, James E Walgenbach 2, George G. Kennedy & James W. Moyer Departments of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC 27695-7630, USA 1 Current address: Merck & Co., Inc. Hillsborough Rd, P.O. Box 450, Three Bridges, NJ 08887, USA 2Department of Entomology, North Carolina State University, 2016 Fanning Bridge Road., Fletcher, NC 28732- 9216, USA Accepted:April25, 1995 Key words: Frankliniella occidentalis, Frankliniella fusca, Thrips tabaci, thrips, tomato, pepper, tobacco, tomato spotted wilt virus Abstract Thrips were surveyed in tomato spotted wilt-susceptible crops in five areas across North Carolina. Tomato, pepper, and tobacco plants in commercial fields were sampled and 30 species of thrips were collected over a 3-year period. The most common species overall was Frankliniella tritici (Fitch). The most common thrips species that are known to vector Tomato Spotted Wilt Virus (TSWV) were Efusca (Hinds), and E occidental& (Pergande). Relatively low numbers of Thrips tabaci Lindeman, another reported vector, were collected. The spatial and temporal occurrence of vectors varied with sampling method, crop species, region of North Carolina, and localized areas within each region. In a laboratory experiment, no difference was detected between the ability of E fusca and E occidentalis to acquire and transmit a local isolate of TSWV. Based on vector efficiency and occurrence, E fusca is considered the most important vector of TSWV in tobacco, whereas both E fusca and E occidentalis are important vectors of TSWV in tomato and pepper. Introduction Tomato Spotted Wilt Virus (TSWV) has an extensive host range (Cho et al., 1987) of which tomato, pep- per, peanut, and tobacco are common, susceptible host crops grown in the southeastern United States. Sev- eral species of Thripidae (Thysanoptera) have been implicated as vectors of this virus (Mau et al., 1991). However, most studies on vector relationships were conducted prior to the recognition of more than one Tospovirus (Bunyaviridae) from what was formerly considered a single virus - TSWV (Law & Moyer, 1990; German et al., 1992). The ability of each thrips species to transmit each Tospovirus has not yet been tested. Thrips acquire TSWV by feeding on infected plants as larvae, but virus transmission to uninfected plants does not occur until after a latent period when thrips are either larvae or adults (Wijkamp & Peters, 1993). Tomato spotted wilt virus replicates in thrips (Ullman et al., 1993) which, once infected, may retain the virus throughout their lives. Thrips do not, however, pass the virus to their progeny (Sakimura, 1962, 1963). Management of TSWV is dependent on a sound understanding of the relationship between thrips dynamics and TSWV infections. In Hawaii, such an approach has been used to develop specific manage- ment strategies (Cho et al., 1989). However, in Hawaii a single thrips species, Frankliniella occidenta- lis (Pergande) is the predominate vector (Cho et al., 1989), whereas in the southeastern United States at least three thrips species may be important in TSWV epidemiol- ogy. In the southeastern United States, TSWV was first detected in the 1970's (Jones & Baker, 1991), and E occidentalis was found in the early 1980's (Beshear, 1983). The coincidence of the establishment ofE occi- dentalis and TSWV provides circumstantial evidence