Colladonus spp. (Hemiptera: Cicadellidae) vectors of X-disease: biology and management in Western United States

The US cherry and stone fruit industries have periodically experienced devastating outbreaks of X-disease phytoplasma (XDP) since the 1930s, with an ongoing epidemic occurring since 2010. This disease is critically impacting Prunus spp. and the stone fruit industry, causing underdeveloped, bitter, and misshapen fruit on economically important crops, primarily cherries, peaches, and nectarines, making the fruit unmarketable. Trees cannot recover from this disease and eventually die if they are not removed. It takes at least 1 yr for symptoms to appear, postinfection, which hinders disease management efforts. The phytoplasma, Candidatus Phytoplasma pruni, is a phloem-limited intracellular bacterium that is spread by grafting and leafhopper (Hemiptera: Cicadellidae) feeding. Several leafhopper species are known to transmit XDP, of which Colladonus spp. are considered the most important vectors in the Western United States and are native to this region. Colladonus spp. feed and oviposit on a wide variety of broadleaf perennial plants, including mallow, alfalfa, and clover. These plants are also hosts of the phytoplasma. In Western United States, these leafhoppers have 3 periods of adult activity: May-June, late July-August, and October. The highest rates of pathogen transmission likely occur during the last 2 activity periods due to the high abundance of leafhoppers and a postharvest increase of XDP titers in trees. Using known activity periods and host plants of the leafhoppers, growers can monitor and strategically manage the vectors, which, when combined with the removal of infected trees and ground-cover hosts, should help limit the spread of X-disease.