Ultrastructure of the ileum of the European corn borer, Ostrinia nubilalis

Abstract

The ileal epithelial cells of the diapause European corn borer were found to have elongated microvilli on their apical and lateral surfaces. Fine filaments were seen extending from tips of microvilli into the intestinal lumen. Fibrous material was present in intercellular spaces, and a basement membrane of uniform thickness persisted. Numerous mitochondria occupied microvilli, cytoplasmic regions surrounding nuclei, and basal parts of the cell. Changes in mitochondrial morphology accompanied changes in the autofluorescent cycle. Progressive development of dense granules, formed from whorled basal parts of microvilli and trapped cellular organelles, was followed during the 8-hr autofluorescent period. Increased autofluorescence correlated directly with development of aggregates of whorls and formation of dense granules. Discharge of granule contents apparently occurred into the haemolymph. Microtubules were commonly seen in cytoplasmic regions of the cell particularly surrounding aggregations of whorls. The presence of smooth endoplasmic reticulum rose as autofluorescence increased as did also the number of ribosomes seen free in the cytoplasm. On favourable sections small plaques were visible on outer plasma membranes of microvilli. Plaques could likewise be seen on membranes within whorls and on disintegrating membranes in dense bodies. The morphology of these cells strengthens the supposition that they are active in absorption and secretion or in ion-exchange processes.