Transmission ofSpiroplasma citriLines and Their Ability to Cross Gut and Salivary Gland Barriers Within the Leafhopper VectorCirculifer tenellus

Spiroplasma citri lines all derived from a single phytopathogenic strain, BR3-3X, but differing in subculturing or maintenance history, were tested for transmission to a susceptible plant host after injection into the leafhopper vector Circulifer tenellus and for their ability to cross both the gut and salivary gland barriers in the insect. BR3-T (a line maintained in turnips by leafhopper transmission) was detected in leafhoppers 18 days after injection and in plants exposed to injected leafhoppers. Plants exposed to leafhoppers injected with BR3-P (a line subcultured in artificial medium more than 130 times) and BR3-G (a line maintained in periwinkle over 8 years by graft transmission) did not become diseased. However, like BR3-T, both of these lines were detected in leafhoppers 18 days after injection. In a separate experiment, a fourth line, BR3-M, that had been passed in liquid culture 43 times, retained insect transmissibility. After leafhoppers fed on suspensions of spiroplasmas, BR3-T was readily recovered from the hemolymph after a 6-wk latent period, whereas BR3-P was rarely recovered and BR3-G was never recovered. Similarly, BR3-T was recovered from solutions fed upon by injected insects after a 14-day latent period, whereas BR3-P was rarely recovered and BR3-G was never recovered. Thus, although all lines multiply within the hemocoel, the ability to traverse insect gut and salivary gland barriers has been lost in BR3-G and significantly impaired in BR3-P.