Functional anatomy of the sharpshooter precibarial valve supports its role in probing behaviors that control inoculation of Xylella fastidiosa

The precibarial valve is a tiny structure in the functional foregut (cibarium and precibarium) of hemipteran insects. Piercing-sucking insects like hemipterans use straw-like mouth parts (stylets) to ingest fluid from plant vascular cells like phloem or xylem. Suction is provided by the cibarium (or cibarial pump), which draws fluid through the stylets into a short canal called the precibarium, then into the cibarium from which the fluid is swallowed into the pharynx then esophagus. The precibarium houses two sets of chemosensilla separated by the tiny precibarial valve, which is operated by its own muscle independent of the muscles powering the cibarium. Despite intensive study, the operational mechanism of the precibarial valve in sharpshooter leafhoppers is not known because the muscle attachment to the valve has not been clearly identified. Such an operational mechanism is important because it controls inoculation of the lethal bacterial pathogen Xylella fastidiosa into healthy crop plants, causing economically devastating diseases such as Pierce's disease of grape, citrus variegated chlorosis, olive quick decline, and numerous leaf scorches. Together, these diseases cause many $billions of damage and control costs worldwide, annually. The present study provides definitive knowledge of how the precibarial valve muscle attaches to the valve in sharpshooter vectors of Xylella fastidiosa. It also proposes a new operation model to control fluid flows responsible for inoculating the pathogen into healthy plants. Such information will aid in development of novel disease management methods such plant resistance to vector performance of inoculation behaviors.