The New, Third-generation, AC-DC Electrical Penetration Graph (EPG) Monitor and Its Usefulness for IPM Research on Vectors of Plant Pathogens

The most rigorous method to identify feeding behaviors of hemipteran vectors of plant pathogens is electrical penetration graph (EPG) monitoring. The purpose of this talk was to review: 1) principals of EPG as a tool for developing novel integrated pest management tools against vectors, and 2) application of EPG to identify feeding behaviors leading to inoculation of Xylella fastidiosa. X. fastidiosa is a xylem-limited bacterium that causes several scorch diseases in important crops, such as Pierce’s disease of grape. Bacteria form a dense biofilm on the foregut cuticle of the glassy-winged sharpshooter, Homalodisca vitripennis (Germar) and other xylem-feeding vectors. Bacteria are inoculated directly from sites in the foregut into a host plant during sharpshooter feeding (i.e. probing of the mouthparts, stylets, into the plant). However, despite nearly 70 years of research, no one had associated specific sharpshooter stylet probing behaviors with inoculation until EPG was employed for such research. Development of the third generation (AC-DC) EPG monitor from the first two generations of monitors (AC and DC) helped define the mechanism of X. fastidiosa inoculation. EPG and other evidence for the salivation-egestion hypothesis for X. fastidiosa inoculation, in which salivation combined with egestion [outward fluid flow] carries bacteria into the xylem, was reviewed. Understanding the inoculation mechanism will aid development of grape varieties resistant to inoculation of X. fastidiosa by sharpshooter vectors