Spiroplasma citri Movement into the Intestines and Salivary Glands of Its Leafhopper Vector, Circulifer tenellus

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Abstract
Spiroplasma citri, a helical, wall-less prokaryote in the class Molli-cutes, is transmitted by the beet leafhopper, Circulifer tenellus. Invasion of leafhopper tissues and cytopathological effects by S. citri were investigated by transmission electron microscopy. All eight cell types of the principle salivary glands, as well as the adjacent muscle cells and the cells of the accessory salivary glands, were colonized by the spiroplas-mas. In both midgut epithelia and salivary gland cells, spiroplasmas usually occurred in membrane-bound cytoplasmic vesicles that often were located near the cell periphery. In several salivary gland cells, spiroplas-mas were also observed within membranous pockets apparently formed by invagination of the plasmalemma beneath intact basal lamina. These observations are consistent with spiroplasma entry into the insect cells by receptor-mediated endocytosis. Cytopathological effects of spiroplasma infection in salivary cells included loss of membrane and basal lamina integrity, presence in some cells of irregular inclusion-like structures containing dense matrices of filamentous material that labeled with anti S. citri antibodies, and apparent disorganization of the endoplasmic reticulum. Compared to the tightly aligned fiber bundles in healthy muscle cells, bundles in spiroplasma-containing muscle cells appeared fragmented and loosely arranged. Such symptoms could contribute to the reduction in longevity and fecundity that has been previously reported for S. citri-infected C. tenellus.