Evidence against the hypothesis that certain plant viruses are transmitted mechanically by aphides

In further experiments on the mode of transmission of persistent and non-persistent plant viruses by insects [R.A.M., xix, p. 230], starved individuals of Myzus persicae after feeding for two minutes on infected plants successfully transmitted Hyoscyamus 3, potato Y, and severe etch viruses, all non-persistent in the vector, from tobacco to a number (up to 10) of successive healthy plants. With all three viruses aphids often failed to infect some healthy plants in the middle of a series, but infected later plants. When infective aphids were fed on two successive healthy plants the number of second plants infected decreased with increasing feeding time on the first healthy plant, none being infected after one hour. Infective aphids allowed short feeding periods on a succession of healthy plants gave infections in a series of nine consecutive healthy plants, while others fed continuously on one healthy plant for a corresponding total period failed to infect any of the second plants. These results are held to contradict the opinion that the non-persistent viruses are transferred mechanically through the cleansing of contaminated stylets of the infective aphids when feeding on a healthy plant. The hypothesis is advanced that the mechanism of transmission is not fundamentally different between the persistent and non-persistent viruses, but while the latter are inactivated by a secretion produced by the aphids during feeding, the former are resistant to it. A close specific relationship between the non-persistent viruses and insects with a particular type of physiology is postulated.