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

The midguts of Bemisia tabaci and Trialeurodes abutilonea are looped s o that the anterior and posterior extremities are in contact with each other. The basal lamina is breached at this point so that opposing ba sal epithelial membranes of either extremity are contiguous. On the an al side of the contact is a ''filter-organ'', consisting of oesophagea l, Malpighian and modified ventricular epithelial cells. Comparison wi th model systems indicates that the filter-organ acts as an osmoregula tory device. It appears that fluid food is directed into the looped mi dgut and concentrated by passive transport of water across the contact point, through the filter-organ, and then into the hindgut. The filte r-organ of both species is attached to the contact point, but in IT: a butilonea 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 indi cate that the midgut can be moved through the petiole, from the abdome n to the thorax, and back again. This, and the absence of Malpighian t ubules, suggests that the midgut services the excretory needs of the f light muscles.