Multiplication of corn stunt spiroplasma in Dalbulus maidis and transmission in vitro, following injection

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Abstract
SUMMARY: Corn stunt spiroplasma (CSS) multiplied in all injected Dulbulus maidis, reaching titres of over 1 × 106 colony forming units (cfu)/insect and 1 × 104 cfu/salivary gland of each insect. Spiroplasmas could be isolated from the haemolymph and from the salivary glands 1 h after injection and at any time subsequently. Insect extract at a concentration greater than the equivalent of 0.1 insects/ml was inhibitory to the growth of CSS in cultures.Helices could be seen in the haemolymph at any time after injection. However, distorted or partially deformed cells and small aggregates were not present until 2–3 wk after injection. The salivary gland cells of injected insects contained membrane‐bound ‘pockets’ or ‘colonies’ packed with pleomorphic organisms, which included some filamentous forms. Intracellular colonies were always on the periphery of cells and were easily detectable by fluorescent microscopy. Both pleomorphic and filamentous forms were also seen intercellularly in the salivary glands.Following injection, transmission of CSS to maize and to sterile feeding solution were compared using 1 day feeding periods. A proportion of injected leafhoppers began to transmit to maize by the third day following injection (5%) and reached a maximum of 72% by day 14. By day 9, 82% of the population had transmitted at least once to plants and by day 12, 100% had transmitted. Similar insects transmitted through membranes to sterile feeding solution on day 4 (3%) reaching a maximum of 62% by day 14.