The digestive system of Diaphorina citri and Bactericera cockerelli (Hemiptera: Psyllidae)

The psyllids Diaphorina citri (Kuwayama) and Bactericera cockerelli (Sulc) (Hemiptera: Psyllidae) are vectors of Candidatus Liberibacter spp., bacterial agents of serious agricultural diseases. The rapidly expanding geographical distributions of these diseases dictate increasing urgency for their control. Therefore, it is important to gain a full understanding of the psyllid digestive system in which the vector-pathogen interactions begin. Their midgut is looped so that the foregut-midgut and midguthindgut transitional regions are grafted together to form a composite tube within a filter chamber sheath. Unwanted sap components could thus be extracted directly into the hindgut, bypassing digestion. The esophageal lumen enters the chamber axially to become the inner midgut lumen. The upper half of this midgut section is bulbous while the lower half is tubular. The tube lumen exits the chamber to become the external midgut lumen, which loops through the hemocoel and reenters the chamber, becoming the inner hindgut lumen. The inner hindgut tracks the adherent inner midgut in an antiparallel direction. The composite tube is helically wound and undergoes one hairpin turn. The inner hindgut straps diagonally across the bulb and then exits the chamber next to the esophagus as the outer hindgut to anus. The source of honeydew, whether filtrate, midgut waste, or both, is questioned. Paired, spherical, primary salivary glands each have a digitate accessory gland and a lateral duct that leads to the stylets. The accessory gland lumen is lined exclusively with intima, whereas the primary gland apical cell membranes are indicated to be more complex.