Temporal dynamics of the transmission of Xylella fastidiosa subsp. pauca by Philaenus spumarius to olive plants

The spittlebug Philaenus spumarius L. (Hemiptera: Aphrophoridae) is the predominant vector of Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae) (Xf) to olive trees in the Apulia Region in Italy. Previous studies focused on assessing the Xf transmission efficiency of spittlebugs and the natural infectivity of the P. spumarius populations. However, the factors that influence Xf transmission by P. spumarius to olive are still largely unknown, and these knowledge gaps hamper the comprehension of the epidemiology of emerging Xf-associated diseases. We have performed two sets of experiments to study the transmission biology of Xf by P. spumarius to understand the kinetics of the bacterial persistence, transmission efficiency and the spread rate of Xf among olive trees in summer and autumn. The results show that i) P. spumarius is a competent Xf vector to olive plants throughout its adult life, ii) the bacterial load in the foregut of the vector increases during the first 2-3 weeks after acquisition and then becomes stable, iii) the transmission rates may vary significantly during the year and under different climatic conditions, and iv) the differential survival of vectors – which is influenced by the age of the insects, the season and climatic conditions – may affect the spread of Xf in olive plants. These results will help to improve both the modelling of the spread of the pathogen, by allowing the effect of the insect vectors to be explicitly incorporated, and the design of effective control and prevention measures against this vector-borne disease.