Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2011
Publication Date: 4/1/2011
Citation: Daane, K.M., Wistrom, C., Shapland, E.B., Sisterson, M.S. 2011. Seasonal abundance of Draeculacephala minerva and other Xylella fastidiosa vectors in California almond orchards and vineyards. Journal of Economic Entomology. 104:367-374. Interpretive Summary: Almond leaf scorch disease (ALS) and Pierce’s disease of grape have been chronic problems for California’s almond and grape growers. Both diseases are caused by Xylella fastidiosa, a bacterial pathogen that is transmitted by xylem feeding insects. In response to reports of increased incidence of ALS, almond orchards throughout California’s Central Valley were surveyed to determine presence and abundance of potential vectors. In conjunction, limited sampling of vineyards located in the central and southern portions of the Central Valley were also completed. The green sharpshooter (Draeculacephala minerva) was the most abundant xylem feeding insect collected from almond orchards. Collections of D. minerva were greatest at sites in the northern Central Valley, where annual rainfall was high and grassy ground cover within orchards was common. In contrast, D. minerva was rare in orchards and vineyards located in the central and southern portions of the Central Valley. While D. minerva was rare in orchards and vineyards in the central and southern Central Valley, D. minerva was abundant in permanent pastures in these areas. Screening of green sharpshooters, collected from almond orchards, for presence of X. fastidiosa found that 1.1% carried the pathogen at a detectable level. The results confirm that the green sharpshooter is still the most abundant vector of ALS-strains of X. fastidiosa in and near almond orchards in the Central Valley. Results from this project will provide growers with information needed to assess risk of ALS.
Technical Abstract: Almond leaf scorch (ALS) is caused by the bacterium Xylella fastidiosa which is transmitted by xylem-feeding sharpshooters and spittlebugs. Reports of increased incidence of ALS-affected almonds in California prompted surveys in three almond-growing regions in California, from June 2003 to September 2005, to determine insect vector species composition and abundance. For comparison, sampling in and near vineyards in the San Joaquin Valley was also completed. More than 42,000 Cicadomorpha were collected, of which 4.8 percent were xylem-feeders, including 1,912 Draeculacephala minerva Ball, five Xyphon fulgida Nottingham, and a single spittlebug (Philaenus spumarius L.). The dominant vector, D. minerva, was more frequently collected in the Sacramento Valley than in the San Joaquin Valley. Season-long sampling indicated that D. minerva was a year-round resident in and/or near almonds in the Sacramento Valley, but not in the San Joaquin Valley. Similarly, D. minerva was rare in vineyards in the San Joaquin Valley, but was abundant in irrigated pastures near vineyards. Draeculacephala minerva was most frequently collected along orchard margins. Peak densities of D. Minerva were observed in summer, the period of time when bacterial titers begin to increase in infected trees. Screening of D. minerva for presence of X. fastidiosa found that 1.1 percent tested positive. All X. fastidiosa-positive D. minerva were collected from inside almond orchards and all carried pathogen strains that matched those collected from ALS-affected almond trees in the same orchard. Of the few X. fulgida and P. spumarius collected, none tested positive for X. fastidiosa.