Using insects to detect, monitor and predict the distribution ofXylella fastidiosa:a case study in Corsica

Abstract

11We sampled ca 2500 specimens of Philaenus spumarius throughout Corsica without a priori 12 on the presence of symptoms on plants. We screened 448 specimens for the presence of 13Xylella fastidiosa (Xf) using qPCR and a custom nested PCR. qPCR appeared versatile and 14 under-estimated the prevalence of Xf. Nested PCR showed that Xf was present in all 15 populations. Molecular results were validated by prediction on the distribution of Xf made 16 from tests conducted on plants, which shows the pertinence of using vectors in risk 17 assessment studies. Xf was detected in tenerals and adults. Thus, P. spumarius could acquire 18Xf from its host plant, mostly Cistus monspeliensis in Corsica, which may act as reservoir for 19 the next season. This contrasts with other observations and suggests that management 20 strategies may have to be adapted on a case-by-case basis. At least two genetic entities and 21 several variants of Xf not yet identified on plants were present in the insects, which suggests 22 ancient introductions of Xf and a probable underestimation of the current diversity of the 23 strains present in Corsica. Interestingly 6% of the specimens carried two subspecies. Studies 24 are wanted to better characterize the strains present in Corsica and know how the disease was 25 introduced, spread and why no sign of a potential epidemic was detected earlier. This study 26shows that, when sensitive enough methods are implemented, insects can be used to predict 27 and better assess the exact distribution of Xf. Insects are indeed easy to collect, Xf multiply 28 only in their foregut and does not become circulative, which facilitates its detection. 29 30

Climate change and the potential distribution ofXylella fastidiosain Europe

“…Balearic Islands, lowlands of Corsica island, south-eastern France and the Apulia region). This suggests that risk maps provided in the present study are reliable for the design of surveys, including ‘spy insects’ survey 68,69 . They may also be helpful to anticipate the spread of the different subspecies and provide guidance on which areas should be targeted for an analysis of local communities of potential vectors and host plants to design management strategies and research projects.…”

Inferring pathogen dynamics from temporal count data: the emergence of Xylella fastidiosa in France is probably not recent

“…11%), and insect vectors tend to be frequent around this host (recent molecular analyses have shown that X. fastidiosa is present in c . 20% of insect vectors Philaenus spumarius collected from several C. monspeliensis populations across Corsica; Cruaud et al ., ). However, this host species has been weakly surveyed (3% of samples) in comparison with much less abundant host species, such as Polygala myrtifolia (12% of samples), which is an ornamental plant with an observed infection rate of 26%.…”

“…Moreover, an analysis of the demography and disease prevalence for a host such as Cistus monspeliensis suggests that it could be, among others, an important component of the hidden compartment. Indeed, C. monspeliensis is very abundant in Corsica (http://www.telabotanica.org), in particular in wild areas; its observed infection rate is quite high (c. 11%), and insect vectors tend to be frequent around this host (recent molecular analyses have shown that X. fastidiosa is present in c. 20% of insect vectors Philaenus spumarius collected from several C. monspeliensis populations across Corsica; Cruaud et al, 2018). However, this host species has been weakly surveyed (3% of samples) in comparison with much less abundant host species, such as Polygala myrtifolia (12% of samples), which is an ornamental plant with an observed infection rate of 26%.…”

Update of the Scientific Opinion on the risks to plant health posed by Xylella fastidiosa in the EU territory

“…Extreme cases include some years after the infection. 22% production in Spain is intensive (Fernandez Escobar et al., ) Control of weeds is a crucial aspect in limiting vector population densities. Vectors and environment have a crucial role in symptoms expression. The vector is wherever olive production is (e.g. Cruaud et al., ). Adults appear in May, are present in orchards from May to September‐October with a population peak in late‐May or June. In some areas of EU (Spain, Greece) vectors are not found in olive orchards during summer.…”