Functional anatomy of the oral region of the potato psyllid (Hemiptera: Psylloidea: Triozidae)

"Candidatus Liberibacter solanacearum", causal agent of zebra chip of potato and veingreening of tomato, is prolific in tissues of the oral region of its vector, Bactericera cockerelli (Sulc). The region has, evolutionarily, reflexed under the head ("opisthognathy"), so that the mandibular stylets are ventral to the maxillary stylets, and both are directed posteriorly. The region includes the labium, furcasternum, and tentorium. The tentorium is a minute, crate-shaped, extremely complex endoskeletal apparatus consisting of preoral and postoral sections, with the primitive mouth in between. Except for certain prominent structures, its functional anatomy is poorly understood, and provisional (generic) terminology is needed to identify them. It is formed from several panel-shaped and rod-shaped invaginations of the preoral orifice. Panels divide the preoral section into four tissue blocks: hypopharynx, epipharynx, and two lateral blocks of questionable homological identity. Those between the hypopharynx and lateral blocks are fluted into "holsters." Holsters are extended into the postoral section as "loading sleeves." Together, both house the stylets. Stylet manipulation muscles are attached to them, not to the stylets themselves. Loading sleeves also function to guide presumptive stylets into their functional positions during a molt. Rods are located in the postoral section, and they form "ecdysial gaps" which also assist in molting. Stylets converge toward the preoral orifice, designed to interlock the maxillars and redirect the mandibulars to their flanks to form a "stylet bundle," and rotate the bundle 90° so that it can curve, about its most-bendable axis, into a cuticular pouch or "crumena" on exit.