Comparative Efficiency of Transmission of Aster Yellows by Elymana virescens and Macrosteles fascifrons and the Relative Concentration of the Causal Agent in the Vectors1

Abstract

When nymphs and adults of Elymana virescens (F.) were caged for 7 days on barley plants, Hordeum vulgare L. var. ‘Vantage’ infected with aster yellows casual agent (AYCA), 26% and 24%, respectively, of the exposed insects subsequently transmitted AYCA to barley seedlings. In comparable concurrent experiments with the aster leafhopper, Macrosteles fascifrons (Stål), 48% and 78% of the nymphal and adult groups, respectively, transmitted the causal agent. An incubation period of 39-46 days was required before 95% of the inoculative E. virescens could transmit, whereas less than 32 days were needed before 85% of the inoculative M. fascifrons transmitted. However, once the leafhoppers of both species became inoculative they were equally consistent in transmitting. When adult E. virescens and M. fascifrons were injected with an inoculum containing AYCA, 16% and 55% of the injected insects, respectively, became inoculative. The concentration of AYCA in the extracts of inoculative E. virescens was about equal to that of inoculative M. fascifrons when the extracts were prepared on the basis of leafhopper weight.