Feeding on healthy versus Xylella fastidiosa (Xf)-infected grapevines influences later blue-green sharpshooter performance of Xf inoculation behaviors

Xylella fastidiosa (Xf)is a foregut-borne bacteriuminoculated into healthy xylem during egestion/salivation behaviors that are represented by the sharpshooter EPG X wave. Our objective was to test whether inoculation behaviors were altered by the likely presence of Xf in the functional foregut of a vector. Age-specific, blue-green sharpshooters, Graphocephala atropunctata (Signoret), were reared on basil to clean their foreguts, then removed from the colony and given one of four pre-EPG treatments: 1) old (>10 weeks) colony adults on basil, 2) young (Xf-infected (symptomatic) grapevine for 4 days. After treatments, stylet probing behaviors of all insects were recorded on healthy grapevine via AC-DC electropenetrography. Waveforms representing putative Xf inoculation (X waves) and other behaviors were statistically compared among treatments. Mean number of occurrences per insect and “total” duration per insect of X waves were highest for insects from healthy grape, lowest for basil (which did not differ by age), and intermediate for Xf-infected grape. These results show that colonization of vectors by Xf (or likely other non-Xf microbes) in grapevine xylem increases the likelihood of performance of microbial inoculation behaviors. This study supports that EPG can capture the dynamic interactions between vectors and the microbes they carry, for application to improving grape resistance to Xf in the future.