Initial and subsequent sites of aster yellows virus infection in a leafhopper vector

Abstract

Aster yellows virus (AYV) was recovered from hemolymph, alimentary canal, salivary glands and ovaries, but not from Malpighian tubules, mycetomes, fat body, testes, or brain of viruliferous leafhoppers, Macrosteles fascifrons (Stål). The presence of virus in the tissues was determined by injecting their extracts into virus-free leafhoppers, then testing the latter singly for inoculativity on aster ( Callistephus chinensis Nees.) seedlings. The virus was first recovered from the alimentary canal immediately after a 3-day acquisition access period and from the hemolymph and salivary glands on day 6 after the start of acquisition. The virus concentration, as indicated by the percentage of injected insects that became inoculative, increased rapidly in the alimentary canal, reached a peak by day 9, but then declined sharply by day 23 and remained at the same low level up to day 30, the longest time tested. The virus concentration in the hemolymph also increased rapidly, reached a peak by day 12, but remained at the same high level up to day 30. In the salivary glands the virus concentration increased gradually, and reached a high level by day 30. The increase of virus concentration in salivary glands was correlated with the increase in transmission by the source leafhoppers. The results suggest that the alimentary canal of the leafhopper is the initial site of virus multiplication, that hemocytes may be the main sites of virus multiplication, and that AYV must reach a certain concentration in the salivary glands before an insect can become inoculative.