Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2013
Publication Date: 2/4/2014
Citation: Krugner, R., Backus, E.A. 2014. Plant water stress effects on stylet probing behaviors of Homalodisca vitripennis (Hemiptera: Cicadellidae) associated with acquisition and inoculation of the bacterium Xylella fastidiosa. Journal of Economic Entomology. 107(1):66-74. Interpretive Summary: Xylella fastidiosa is a bacterium that causes almond leaf scorch disease, citrus variegated chlorosis, and Pierce’s disease of grapevines. These diseases can severely damage plants, reducing fruit yield and quality, and shortening the productive life of the crop. This important bacterium is transmitted from plant to plant by several species of leafhoppers, including the glassy-winged sharpshooter, a relatively recent invader of California. A sound understanding of factors controlling the spread of bacteria is critically important to management efforts. Irrigation is the most significant input in California agriculture, and future climate projection models predict reduced water availability to farmland. Scientists have developed water-saving strategies to maximize water use efficiency by reducing irrigation during drought-tolerant growth stages of a plant. Therefore, knowledge of the effects of plant water stress caused by either natural drought periods or controlled deficit irrigation on the spread of bacteria is key to developing disease management strategies. In controlled studies where glassy-winged sharpshooters were exposed to fully irrigated and water-stressed plants, irrigation treatment affected feeding behaviors in ways that could change the rate of spread of bacteria. Specifically, long and frequent feeding events of behaviors previously associated with the spread of the bacteria were observed only in fully irrigated plants, which suggests that plant water stress may reduce spread of the bacteria. Results provided insights to disease epidemiology and support that application of regulated deficit irrigation has the potential to reduce incidence of diseases caused by X. fastidiosa by decreasing pathogen transmission efficiency by leafhoppers.
Technical Abstract: The glassy-winged sharpshooter, Homalodisca vitripennis, is a xylem fluid-ingesting leafhopper that transmits Xylella fastidiosa, the causal agent of several plant diseases in the Americas. While the role of plant water stress on the population density and dispersal of H. vitripennis has been studied, nothing is known about the effects of plant water stress on transmission of X. fastidiosa by H. vitripennis. A laboratory study was conducted to determine the influence of plant water stress on sharpshooter stylet probing behaviors associated with acquisition and inoculation of X. fastidiosa. Electrical penetration graph was used to monitor H. vitripennis feeding behaviors for 20-h periods on citrus, Citrus sinensis, and almond, Prunus dulcis, plants subjected to levels of water stress. Adult H. vitripennis successfully located xylem vessels, then performed behaviors related to the evaluation of the xylem cell and fluid, and finally ingested xylem fluid from citrus and almond plants under the tested fluid tensions ranging from -5.5 to -33.0 Bars and -6.0 to -24.5 Bars, respectively. In general, long and frequent feeding events associated with acquisition and inoculation of X. fastidiosa were observed only in fully irrigated plants (i.e., > -10 Bars), which suggests that even low levels of plant water stress may reduce the spread of X. fastidiosa. Results provided insights to disease epidemiology and support that application of regulated deficit irrigation has the potential to reduce the incidence of diseases caused by X. fastidiosa by reducing the number of vectors and by decreasing pathogen transmission efficiency.