On the Mechanism of Transmission of Non-Persistent Phytopathogenic Viruses by Aphids

Abstract

The following is a working hypothesis, based on published data, to elucidate the mechanism of transmission of nonpersistent viruses by aphids the stylets of the vector become contaminated with virus during probing in infected tissues. Only this virus is of significance in disease transmission, and ingested virus plays no part in the process. Some of the virus on the stylets is inactivated by salivary fluids. Viruses differ in their susceptibility to this inhibition and different species of aphids vary in the production of the inhibitor. Fasting decreases the activity of the salivary inhibitors. Experimental evidence has been sought to determine whether virus is carried on the stylets, and whether salivary secretions are inhibitory. Although direct proof of these points is lacking, there is evidence that infective virus is carried mechanically, and that some viruses are sensitive to components of the saliva of certain insects. A study of the effects of fasting on the physiology of aphid vectors has shown that fasting has no effect on digestive enzyme formation, the rate of penetration of the stylets into the leaf, or the amount of plant material ingested. Fasting does have an effect on aphid feeding behavior and on the production of saliva. Finally, explanations for vector specificity and differences in vector efficiency are examined. It is concluded that there is evidence in favor of the working hypothesis.