Sex and Age of Macrosteles fascifrons1 in Relation to the Transmission of the Clover Proliferation Causal Agent2

Abstract

The ability of aster leafhoppers, Macrosteles fascifrons (Stål), to transmit clover proliferation causal agent (CPrCA) to aster, Callistephus chinensis Nees, plants depends on the sex and age of the insects at the time they are allowed to feed on infected plants. When adult leafhoppers were given acquisition access feeds for various times, transmission by females increased from 14% after a 3-day feed to 34% after a 21-day feed. With males, no transmission occurred after feeds of 3 and 7 days, and only 5% transmitted CPrCA after a 21-day feed. When nymphs were given acquisition access feeds of 7 days, 20% of the females and 11% of the males subsequently transmitted the causal agent. Prolonging the acquisition access period to 14 days increased the transmission by females (39%) but not by the males (12%). Injection of adult insects with inocula containing CPrCA resulted in 27% of the females but only 3% of the males becoming infective. CPrCA could be recovered, using infectivity bioassays, from the alimentary canals of both male and female leafhoppers at various times after they had been exposed to diseased plants. CPrCA was first recovered from the alimentary canals of both male and female leafhoppers at day 14 after the start of a 7-day acquisition access feed. In males the relative concentration of causal agent decreased by day 21 and then remained at about the same level. In females, the concentration increased sharply by day 21 and then decreased by day 28. Increase in concentration of CPrCA in the alimentary canal suggests that the causal agent multiplies in this organ in both male and female leafhoppers but to a lesser extent in the males. The results of these experiments suggest that tissues of the male leafhopper are less susceptible to CPrCA infection than are those of the female. If this hypothesis is fact it would explain the difference in transmission between the sexes.