Muscle movements that control inoculation of Xylella fastidiosa are revealed by head X-rays of feeding glassy-winged sharpshooters

The mechanism of inoculation of the Pierce’s disease bacterium, Xylella fastidiosa (Xf), by vectors such as the glassy-winged sharpshooter (GWSS) is still unknown, despite nearly 70 years of study. Research in support of the recent egestion-salivation hypothesis for Xf inoculation is presented. Two important steps in this hypothesis are: 1) uptake of saliva into the vector’s precibarium, causing the attached Xf bacteria therein to loosen from the cuticle, followed by 2) expulsion (egestion) of saliva containing loosened bacteria into the xylem prior to ingestion. To directly observe actions of cibarial muscles controlling ingestion (uptake) and egestion of fluid from the precibarium, live, feeding GWSS were X-rayed and video-recorded in the Advanced Photon Source at the Argonne National Laboratory. Simultaneously, feeding of X-rayed sharpshooters was also recorded using AC/DC Electrical Penetration Graph (EPG) technology. Cibarial muscles were observed to be attached to two sets of tracheae (air tubes) inside the head. The trachea moved at different times during feeding, clearly indicating muscle movement. Video results support that waveform B1 is correlated with muscle movements controlling uptake of small amounts of fluid, presumably into the precibarium alone; C1 is correlated with movements for rapid, discharging egestion from the cibarium; and C2 is correlated with movements for uptake of large amounts of fluid into the precibarium and cibarium, for ingestion (swallowing). Implications for the mechanism of inoculation are discussed.