Evidence that explains absence of a latent period for Xylella fastidiosa in its sharpshooter vectors

The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), and other sharpshooter (Cicadelline) leafhoppers, transmit Xylella fastidiosa (Xf) the causative agent of Pierce’s disease of grapevine and other scorch diseases. Past research has supported that vectors have virtually no latent period for X. fastidiosa, because sharpshooters are able to inoculate bacteria within one hour of uptake, from either infected plants or artificial diets. Such findings usually have been interpreted as evidence of rapid attachment of bacteria onto the cuticle of the functional foregut. However, results presented herein show that green fluorescent protein-expressing (GFP) Xf, taken up by GWSS given a 24-hour acquisition access period (AAP) on artificial diets, did not bind to the foregut according to confocal examination immediately after the AAP. Acquisition diets contained 10⁸ CFU of bacteria primed for cuticular attachment. In addition, following the 24 hour AAP, sharpshooters were given an additional 24-hour holding period on bacteria-free diet or plants. Bacteria were not detected via quantitative polymerase chain reaction (qPCR) inside either insects or plants immediately after the holding period. In contrast, numerous GFP Xf were expelled into confocal-imaged salivary deposits, when sharpshooters were offered bacteria-free diet sachets immediately after the AAP. One possible explanation for these results is that bacteria could be held in a column of fluid in the stylets for minutes to hours after ingestion from diets. If so, then egestion of these unbound bacteria could represent a new inoculation mechanism that explains the absence of a latent period for Xf.