TRANSMISSION OF TOMATO SPOTTED WILT VIRUS IN ONTARIO GREENHOUSES BY FRANKLINIELLA-OCCIDENTALIS

Epidemics caused by tomato spotted wilt virus (TSWV) in Dahlia, Lycopersicon, Sinningia, and Tagetes species in commercial greenhouses in Ontario, Canada, were associated with populations of the western flower thrips Frankliniella occidentalis, a species which has not been reported in eastern Canada. The thrips transmitted both a tipblight strain and a mild strain of the virus. All cultivars of tomato (L. esculentum) recommended for use in commercial greenhouses developed foliage symptoms and severe fruit symptoms when infected. The percentage of plants that became infected when thrips (2-6/plant) were caged on L. esculentum and on Gomphrena globosa ranged from ca. 20 to 30% and 40 to 80%, respectively. The maximum calculated proportions of thrips which transmitted virus was 18% when thrips were caged on L. esculentum and 33% when caged on G. globosa. The incidence of infection varied in groups of juvenile, nonflowering L. esculentum (90%), G. globosa (80%), D. pinnata .times. coccinea (75%), and T. patula (30%) openly exposed in a growth room for 7 days to a colony of thrips reared on TSWV-infected plants. The latter results indicated that attraction of thrips may not be greatly influenced by the presence of flowers in certain plant species.