The spatial distribution of insect-borne plant-virus diseases

Various workers have proposed formulae to express the spatial distribution of insect-borne diseases. All the published data examined, as well as the Rothamsted data for the spread of rugose mosaic and leaf-roll from point sources in potato crops, were fitted as well by the simple empirical expression log I=a + bx as by more complex expressions ( I = number of infective punctures at a distance x from the source after a given time, and a and b are constants for any one given set of field conditions). It is suggested that distances should always be given in metres, in order to give comparable results from one investigation to another. In the analysis of data on rugose mosaic and leaf-roll in'different years, it is shown that a and b vary independently.