The Relationship ofSpiroplasma citriandCirculifer tenellus

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Abstract
The causal agent of citrus stubborn disease, S. citri, multiplies in its natural leafhopper vector, C. tenellus. One day following injection, the total assayable colony-forming units (CFU) decreased by 0.5 log10 units and then gradually increased to a maximum of between 104 and 105 CFU/insect at 15 days after injection. No CFU were observed from insects injected with sterile liquid medium. S. citri also caused premature death of some C. tenellus whether acquisition was by injection, membrane feeding, or feeding on plants infected with S. citri. Cells of S. citri were first observed by EM in the salivary glands of C. tenellus 10 days after the insects were injected with S. citri. Large concentrations of S. citri usually in irregular pockets, were observed adjacent to the acini of the salivary glands 15 days after injection. No bodies resembling S. citri were found in the salivary glands of healthy leafhoppers. Sequential EM studies of S. citri in C. tenellus following membrane feeding can be summarized as follows: S. citri enters the gut lumen after feeding, where a number are digested or destroyed. Surviving cells pass through the gut wall into the epithelial cells where they may multiply. They continue to move toward and through the basement membrane of the intestine and into the hemocoel, where further multiplication occurs. S. citri is then transported by the hemolymph to the salivary glands, from which it can be injected into plants [citrus] via salivary secretion during feeding.

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