Xylella fastidiosa inoculation behaviors (EPG X wave) are performed differently by blue-green sharpshooters based on infection status of prior probing host

Authors: RODDEE, JARIYA - Suranaree University Of Technology; Backus, Elaine; CERVANTES, FELIX - Bayer Corporation; HANBOONSONG, Y - Khon Kaen University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2023
Publication Date: 3/29/2023
Citation: Roddee, J., Backus, E.A., Cervantes, F.A., Hanboonsong, Y. 2023. Xylella fastidiosa inoculation behaviors (EPG X wave) are performed differently by blue-green sharpshooters based on infection status of prior probing host. Journal of Economic Entomology. 116(3):697-712. https://doi.org/10.1093/jee/toad043.
DOI: https://doi.org/10.1093/jee/toad043

Interpretive Summary: Pierce’s disease (PD) is a lethal scorching disease of grapevines caused by the bacterium Xylella fastidiosa (Xf), which threatens the $5 billion per year grape crop in California. Xf is vector-borne and transmitted by sharpshooter leafhoppers and adult spittlebugs worldwide. Xf is also a highly invasive pathogen that co-opts native vector species when it arrives in a new habitat, such as in Italy where it causes economically devastating Olive Quick-decline Disease transmitted by the spittlebug Philaenus spumarius L. Vector-microbe interactions of Xf are complicated and vary rapidly over time because the bacteria do not circulate in the vector’s body. Instead, they colonize only the functional foregut and are rapidly and alternately swept in (during acquisition) and out (during inoculation) of the mouth parts during feeding. “Freezing” this action by attempting to detect bacteria is challenging. However, a technique called electropenetrography (EPG) can capture in real-time the feeding behaviors of the vector that control such fluid movements, thereby providing a window into this otherwise untraceable, dynamic process. This project used EPG to determine whether performance of inoculation behaviors (fluid ejection and salivation) differ when Xf bacteria have colonized or are absent from the vector’s functional foregut. Results show that colonization of vectors by Xf (or additionally other non-Xf microbes) increases the likelihood that the insect will perform microbial inoculation behaviors. This study supports that EPG can be used to visualize the dynamic interactions between vectors and the microbes they carry and will be applied to improving grape resistance to Xf in the future.

Technical Abstract: Xylella fastidiosa (Xf) is a foregut-borne bacterium inoculated into healthy xylem during egestion/salivation behaviors that are likely 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 (<2 weeks) colony adults on basil, 3) young colony adults held on healthy grapevine for 4 days, and 4) young colony adults held on 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 (XB1 [salivation and rinsing egestion] and XC1 [discharge egestion]) and other behaviors were statistically compared among treatments. Mean number of occurrences (events) per insect and “total” duration per insect of XB1, XC1, and four other waveforms 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 be used to visualize the dynamic interactions between vectors and the microbes they carry and will be applied to improving grape resistance to Xf in the future.