Studies on transmission of Xylella fastidiosa by insect vectors
The transmission of Xylella fastidiosa (EPPO A1 quarantine pest) by insect vectors was studied in California (US), in order to determine how the number of viable X. fastidiosa in plants is related to vector transmission efficiency. A strain of X. fastidiosa causing grapevine Pierce’s disease and two efficient vectors Graphocephala minerva and Carneocephala fulgida were used. Bacterial populations and efficiency of transmission were measured in five host plants (Vitis vinifera cv. Pinot noir, Rubus discolor, Artemisia douglasiana, Echinochloa crus-galli, Cynodon dactylon) at various time intervals after insect inoculation of plants. On Cynodon dactylon, no transmission by vectors or recoveries of X. fastidiosa were obtained, and the authors query why this plant species was considered as a host in previous studies. On other hosts, results show that X. fastidiosa has to multiply to reach a threshold in the plant, before transmission by vectors can occur. Populations have to reach a level between 104 and 105 CFU/g. It was also observed that the rate of transmission increase with the level of X. fastidiosa in the plants. Insects fed on grapevine and R. discolor, which supported larger populations of the bacterium, also had higher rates of transmission than insects fed on Artemisia douglasiana and Echinochloa crus-galli.
Sources
Hill, B.L.; Purcell, A.H. (1997) Populations of Xylella fastidiosa in plants required for transmission by an efficient vector.
Phytopathology, 87(12), 1197-1201.