Population dynamics of insect vectors of Xylella fastidiosa in California almond nurseries: An assessment of plant vulnerability to almond leaf scorch disease

Almond leaf scorch (ALS) is caused by the xylem-limited bacterium Xylella fastidiosa, which also infects ~145 other plant species in California. The pathogen is transmitted by xylem-fluid feeding insects including sharpshooters and spittlebugs. Within almond orchards tree-to-tree spread of the pathogen appears to be rare, thus most infections are due to the movement of inoculative vectors into the orchard. The abundance of potential inocula and insect vectors outside almond nurseries was quantified. The objectives of the study were to: 1) monitor the movement and seasonal abundance of insect vectors in vegetation near almond nurseries; and 2) monitor plant phenology in habitats surrounding almond nurseries to determine their potential to serve as hosts for the pathogen and/or vector. Draeculacephala minerva Ball was the most common vector collected. Population densities of D. minerva were higher in irrigated pastures than in alfalfa or mixed weedy environments. As the season progressed and plants dried in non-irrigated habitats, the abundance of D. minerva sharply declined. Potential management strategies for ALS at the nursery level are discussed based on observed patterns of seasonal insect abundance and incidence of X. fastidiosa in potential source plants along with previous records of plants as host for X. fastidiosa.