SPATIAL AND TEMPORAL DYNAMICS OF TOMATO MOTTLE GEMINIVIRUS AND BEMISIA-TABACI (GENN) IN FLORIDA TOMATO FIELDS

Progression of tomato mottle geminivirus (TMoV), and abundance and dis persion of adult whitefly, Bemisia tabaci (Gennadius) B biotype, were monitored in 1992 and 1993 in 91 experimental plots located on 10 comm ercial tomato farms. Prior to harvest (73 to 75 days post plant) withi n-row aggregation of tomato mottle-infected plants was detected by mea ns of ordinary runs analysis in only two of 14 plots that exhibited a disease incidence greater than 5%. At harvest (95 to 107 days post pla nt), within-row aggregation was detected in 11 of 21 plots. Significan t clustering of diseased plants occurred in only 7% of plots analyzed with Gray's two-dimensional distance class analysis. The observed patt ern of disease in these plots was characterized as having numerous sma ll clusters of symptomatic plants scattered throughout plots prior to harvest. No relationship was observed between disease incidence and th e degree of aggregation. Dispersion patterns of adult B. tabaci fluctu ated throughout the season with values of the Morisita's index ranging from less than 1 (indicating a uniform dispersion pattern) to greater than 2 (indicating an aggregated pattern). Abundant sources of immigr ating viruliferous whitefly vectors, rather than secondary spread with in fields, appeared to be the driving force behind epidemics of tomato mottle in this production system characterized by frequent applicatio ns of insecticides.