Location: Crop Diseases, Pests and Genetics
Title: Glassy-winged sharpshooter can use a mechanical mechanism to inoculate Xylella fastidiosa into grapevines Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 13, 2014
Publication Date: N/A
Technical Abstract: Xylem-feeding leafhoppers such as the glassy-winged sharpshooter, Homalodisca vitripennis (Cicadellidae: Cicadellinae), are thought to inoculate the bacterium Xylella fastidiosa (Xf) from colonies bound to cuticle of the sharpshooter’s functional foregut (precibarium and cibarium). The mechanism of inoculation is hypothesized to be egestion and salivation combined, based on findings from EPG and histology. Evidence supporting this hypothesis may explain absence of a latent period in Xf transmission. Sharpshooters were enclosed in sachets to feed upon diet containing green fluorescent protein (GFP)-expressing Xf for 24 hours. Each insect then was serially transferred to two new sachets containing diet lacking bacteria (clean diets) and observed for 1-4 probes on each sachet. Insect foreguts and parafilm diet covers were examined via confocal microscopy; liquid diets were streaked onto Xf media to attempt culturing. Extensive colonies of non-GFP-expressing bacteria were bound to the functional foregut of all insects examined (n=48), thus the foregut cuticle was not swept clean. Yet, no GFP-Xf cells were bound to the foreguts, nor were GFP-Xf cells cultured from the liquid portion of clean diets (n=57). In contrast, dense collections of GFP-Xf bacteria were found inside salivary deposits adhering to the surface of clean parafilm sachets, or inside small salivary sheaths penetrating through the parafilm into clean diets. We hypothesize that GFP-Xf cells were held in a column of fluid in the foregut, then egested into simultaneously extruded deposits of sheath saliva on clean diets. To test the column-of-fluid hypothesis, fluorescent microspheres (incapable of binding to cuticle) were substituted for GFP-Xf and the same study was repeated. Once again, salivary sheaths were florescent from dense accumulations of microspheres and no fluorescence was detected in diets. Thus, particles taken up into the functional foregut, perhaps including Xf cells, do not have to bind to the cuticle before they can be egested.