Development of a PCR-based diagnostic method to detect DNA of Philaenus (Hemiptera: Aphrophoridae), vector of Xylella fastidiosa, in the gut of spiders

Abstract: In the last years, the phytopathogen Xylella fastidiosa (Xf) has been devastated olive groves throughout Southern Italy in the form of the disease known as “Olive Quick Decline Syndrome”. Since there’s no cure for Xf, vector control is recognized as the main protection measure to reduce the spread of this pathogen. However, the implementation of sustainable and ecological measures to control the population of Philaenus spumarius, the main vector of Xf, is required. Generalist predators, such as spiders, are naturally presented in the ecosystems and, they can play an important role in vector control. But the identification of predation in the field may not always be possible. So, the development of a PCR-based diagnostic method may be a reliable tool to accurately detect predation events and potential predators. Therefore, the main goal of this work was to design and evaluate taxon-specific primers within the mitochondrial cytochrome oxidase I (COI) and cytochrome b (cytB) genes, to be used for a PCR-based diagnostic method aimed to detect Philaenus sp. in the gut of the spider Xysticus acerbus Thorell, 1872 (Thomisidae). For that, a set of 20 primers were designed and tested for specificity, sensitivity, and efficiency to detect the presence of Philaenus sp. DNA in the gut of X. acerbus. Feeding trials with the X. acerbus were conducted to estimate the time at which prey DNA is detectable within the predator after ingestion. Finally, spiders were also collected in the field to confirming the predation of Philaenus sp. Among the pair primers tested, one showed great sensitivity and specificity for Philaenus sp. and when applied in the feeding assay the primer pair successfully amplified the degraded DNA of Philaenus sp. in the gut of the spider. According to the Probit regression, there is a 50 % probability of detecting Philaenus sp. DNA 82 hours after ingestion. 20 % of spiders collected in the field tested positive for P. spumarius. This study demonstrates that this molecular tool can provide an estimation of predator efficiency of spiders over Philaenus sp. in the field.