THE ALIMENTARY CANAL OF BEMISIA-TABACI AND TRIALEURODES ABUTILONEA (HOMOPTERA, STERNORRHYNCHI) - HISTOLOGY, ULTRASTRUCTURE AND CORRELATIONS TO FUNCTION

The midguts of Bemisia tabaci and Trialeurodes abutilonea are looped so that the anterior and posterior extremities are in contact with each other. The basal lamina is breached at this point so that opposing basal epithelial membranes of either extremity are contiguous. On the anal side of the contact is a ''filter-organ'', consisting of oesophageal, Malpighian and modified ventricular epithelial cells. Comparison with model systems indicates that the filter-organ acts as an osmoregulatory device. It appears that fluid food is directed into the looped midgut and concentrated by passive transport of water across the contact point, through the filter-organ, and then into the hindgut. The filter-organ of both species is attached to the contact point, but in IT: abutilonea it is thereafter suspended in the alimentary lumen, free of the alimentary wall. In B. tabaci, the oesophageal cells of the filter-organ are attached to the alimentary wall. This constitutes the major difference in gut histology between the two species. Dissections indicate that the midgut can be moved through the petiole, from the abdomen to the thorax, and back again. This, and the absence of Malpighian tubules, suggests that the midgut services the excretory needs of the flight muscles.