The oral box and its relationship to transmission of Ca. Liberibacter in the potato psyllid Bactericera cockerelli (Sulc) and Asian citrus psyllid Diaphorina citri (Kuwayama)

In several insect systems, fastidious bacteria have been observed and/or are expected to associate with the oral region after exposure to the infection source.

The potato psyllid and Asian citrus psyllid oral region is a quadrate structure, which we refer to as the “oral box”. It is directly posterior to, and approximately the same size as, the clypeus. The edges of the box are sclerotized rods. The lateral, dorsal and ventral faces are membranous fenestrations. The 2 maxillary and 2 mandibular stylets have widely separate points of origin, and each point is affixed to the inner surfaces of the lateral fenestrations. The anterior face of the box is open to the muscle complex inside the clypeus. The ventral face tapers into a portal through which the stylets converge and unite into the functional haustellum, then extend exteriorly to the length needed for feeding. Their divergence from each other within the box requires that the two canals, salivary and food, of the united stylets transition into three ducts: the left and right salivary ducts, and the esophagus.

This transition represents the anterior most point at which bacteria could feasibly enter the stylets, leading to the hypothesis that Ca. Liberibacter could potentially gain access into the oral box from the hemolymph, in contrast to ducal transport models.

Numerous Ca. Liberibacter-like cells have been observed by TEM within the oral box of the potato psyllid. Consequently, identification and characterization of the sites within the oral box that participate in Ca. Liberibacter ingestion, and/or acquisition, and/or transmission is a research directive of high priority.