Insects have an active role in the transmission of many pathogens, such as Erwinia tracheiphila which causes bacterial wilt of cucurbits. Transmitted by the striped cucumber beetle (Acalymma vittatum) and the spotted cucumber beetle (Diabroticaundecimpunctata howardi), E. tracheiphila grows rapidly in the vascular system, causing plugging of the vessels with bacteria, gums, resins, and polysaccharides. This viscous ooze can be seen stretching between the cut ends of the cucurbit stem.
Photograph courtesy of M. P. Hoffmann from the Compendium of Cucurbit Diseases.
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