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 dispersion of adult whitefly, Bemisia tabaci (Gennadius) B biotype, were monitored in 1992 and 1993 in 91 experimental plots located on 10 commercial tomato farms. Prior to harvest (73 to 75 days post plant) within-row aggregation of tomato mottle-infected plants was detected by means 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 plant), within-row aggregation was detected in 11 of 21 plots. Significant clustering of diseased plants occurred in only 7% of plots analyzed with Gray's two-dimensional distance class analysis. The observed pattern of disease in these plots was characterized as having numerous small clusters of symptomatic plants scattered throughout plots prior to harvest. No relationship was observed between disease incidence and the degree of aggregation. Dispersion patterns of adult B. tabaci fluctuated 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 immigrating viruliferous whitefly vectors, rather than secondary spread within fields, appeared to be the driving force behind epidemics of tomato mottle in this production system characterized by frequent applications of insecticides.