VIEW ARTICLE

Vector Relations

The Relationship of Spiroplasma citri and Circulifer tenellus. Hsing- Yeh Liu, Postdoctoral research plant pathologist, Department of Plant Pathology, University of California, Riverside 92521, Present address: USDA-ARS-WR, P.O. Box 5098, Salinas, CA 93915; D. J. Gumpf(2), G. N. Oldfield(3), and E. C. Calavan(4). (2)(4)Associate professor, and professor emeritus, respectively, Department of Plant Pathology, University of California, Riverside 92521; (3)Research entomologist, Agricultural Research Service, U.S. Department of Agriculture, Western Region, Boyden Entomology Laboratory, Riverside, CA 92521. Phytopathology 73:585-590. Accepted for publication 21 October 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-585.

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 per 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 electron microscopy 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 electron microscopy 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 of the cells of S. citri 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 via salivary secretion during feeding.