Breakthroughs in understanding the Bemisia tabaci digestive system as it pertains to begomovirus transmission

Fifteen years of study by numerous authors on the digestive anatomy of B. tabaci can now be evaluated with regard to what is currently known or accepted, and what future lines of research are needed, in pursuit of a full understanding of geminivirus transmission. Transmission is circulative, from the stylets, down the esophagus, to the ventriculus, filter organ and/or hindgut, where transepithelial transport and hemolymphic chaperones bring virus to the salivary glands. Since the midgut is capable of directly, physically, contacting the salivary glands by transposing itself from abdomen, through petiole, to the thoracic/cervical region, disembarkation of the virus from the gut could occur anywhere during this action. ISH and immunolocalization yield intense labeling in the primary glands (PSGs) but not in the accessory glands (ASGs). ASGs are indicated to be cyclical in their secretory capacities, and may harbor virus only at certain, brief stages. Mapping studies, generated from light and electron microscopy of extirpated and nonextirpated glands, show that the PSGs have at least 3 secretory cell types. One is shown to make material for forming the stylet sheath. Several other cell types, and an internal ducal system, have been located and described. Immunolocalization technique yields the best preservation of cytostructure, and therefore the highest clarity of association between virus and PSG cytology. Results from this technique, combined with mapping, allow for the identification of one cell type that virus specifically associates with.