The Aster Yellows phytoplasma is transferred by the leaf hopper vector. After the leafhopper feeds on an infected watercress plant, the leafhopper may become infected. It may take about two to four weeks for the phytoplasma to increase itself within the leafhopper (vector) gut system (hemolymph). Then it moves to the salivary glands from where it is then injected into the phloem (conductive vascular plant tissue) of the watercress plant during insect feeding. Once a leafhopper becomes infected, it can transmit the phytoplasma for life (persistent vectors). Eggs from infected female leafhoppers are not infected with phytoplasma.