of disease Citrus stubborn disease Several studies conducted in the 1970s and 1980s have showed that the beet leafhopper is a vector (epidemiology) of the Spiroplasma citri prokaryote which is the causal agent of the Citrus Stubborn Disease. Mode of transmission The bacterium S. citri is initially acquired by the leafhopper through feeding on a plant that has already been infected. Through feeding, the prokaryote enters the gut of the beet leafhopper where most of its cells are killed, but some do survive. These surviving organisms then enter the epithelial cells of the intestine and multiply. Eventually the organisms are able to make their way into the hemocoel of the insect through which they are transferred to the insect’s salivary glands. When the insect then feeds on healthy plants, the prokaryotes enter the phloem of the plant and thus infect the new plant. One study has shown that this process of transmission also has negative effects on the leafhopper itself, where significant numbers of leafhoppers may die after being infected with S. citri. The researchers suggest that this increased mortality may be as a result of ingesting toxins that are produced either by S. citri itself or by plants defending themselves against the pathogen. In any case, these toxins have a significant on the longevity of infected beet leafhoppers. Another study tested some of the characteristics that are important for transmission of S. citri by the beet leafhopper. Researchers tested the impacts of modes of acquisition on the latent period of S. citri within the leafhopper and found that insects that had been injected directly with the prokaryote in their gut had the lowest latency period of 10 days followed by leafhoppers who had ingested the pathogen from an infected plant (16 days). In testing the time taken for the insects to acquire S. citri, the acquisition access period, researchers found that a time period of at least 6 hours of feeding on S. citri cultures were required for insects to acquire the pathogen. However this study should be viewed critically as insects were membrane fed a culture of the organism to determine this time period and actual results may vary when insects feed on an infected plants. The study also found that the numbers of host plants that were infected with S. citri increased with the numbers of infected leafhoppers that were feeding on these plants. Movements of Spiroplasma