Of more than a dozen members of the genus Tospovirus, Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV) are among the most damaging viruses found in North America (3). TSWV is a major problem in vegetable and field crops, whereas INSV is commonly encountered in the floriculture and nursery industries. TSWV is transmitted by several thrips species, of which the western flower thrips (WFT, Frankliniella occidentalis Pergande) is the most predominant vector. INSV has been reported to be transmitted only by WFT (1). To determine if tobacco thrips (TT, F. fusca Hinds) can transmit INSV, a virus-free culture of TT was reared on detached peanut cv. Florunner leaves in 0.5-liter polypropylene cups with closed lids at 25 ± 2°C with constant light. Fresh peanut leaves were exchanged every 2 to 3 days to maintain the thrips colony. For transmission studies, adult thrips were confined on peanut leaves for 24 h for oviposition and then the peanut leaves, sans adults thrips, were transferred to a new cup. Leaves were examined daily for larval emergence, and similarly aged first instar larvae (<12 h old) were given an acquisition access period of 24 to 48 h on INSV-infected detached leaves of Emilia sonchifolia. The larvae were subsequently transferred to healthy peanut leaves and reared until adult emergence. Groups of 10 adults per plant were given a 48-h inoculation access period on 10-day-old healthy E. sonchifolia seedlings. Thrips were subsequently killed, and the plants were maintained in a growth chamber at 28 ± 2°C, and with a 16/8 light/dark photoperiod. Transmission studies were repeated 10 times with different sources of infected plants and different batches of larvae following acquisition access periods. Seven to ten days after inoculation, plants developed symptoms consisting of chlorotic spots, mosaic, and mottling. The presence of INSV in these symptomatic plants was confirmed by ELISA using INSV ImmunoStrip Test (Agdia, Inc., Elkhart, IN) and by reverse transcription-polymerase chain reaction assay with primers specific to the INSV-NSs gene. Our results demonstrate that TT can serve as a vector of INSV. INSV has been reported in peanut in the southeastern United States (2). WFT and TT transmit TSWV in peanuts, with the latter being the predominant vector species in Georgia and other parts of the region. TT transmission of INSV is of concern because of the increased incidence in recent years of INSV in peanuts and the potential for synergistic or gene exchange between TSWV and INSV, since mixed infections with both viruses have been observed (4).
References: (1) M. L. Daughtrey et al. Plant Dis. 81:1220, 1997. (2) S. S. Pappu et al. Plant Dis. 83:966, 1999. (3). J. L. Sherwood et al. Pages 1034--1040 in: Encyclopedia of Plant Pathology. C. Maloy and T. D. Murray, eds. John Wiley and Sons, Inc., New York, 2001. (4) L. Wells et al. Phytopathology (Abstr.) 94:S94, 2001.