Spread of Xylella fastidiosa in Majorca Island Agroecosystems: Interaction Between Insect Vectors, Woody Hosts and Bacterial Subspecies

Abstract

Xylella fastidiosa (XF) is a gram-negative bacterium naturally transmitted by xylem sap-feeding insects that causes serious plant diseases. Since 2016, three subspecies of XF have been identified in Majorca: fastidiosa, multiplex, and pauca. Only the Aphrophoridae Philaenus spumarius (PS) and Neophilaenus campestris (NC) have been reported as potential insect vectors for XF in Majorca and the Balearic Islands. This study aims to understand the spread of XF and propose effective and feasible strategies for its control. Eight plots were studied from 2019 to 2021: four almond orchards and four vineyards. The crops and the surrounding vegetation were sampled for XF, phytoplasmas, and potential vectors. DNA from plants and insects was extracted and amplified by three quantitative PCR (qPCR) methods, allowing subspecies identification. The results confirmed the prevalence of PS on the island, with also the presence of NC at lower levels. During the summer months, PS captures were mainly in the wild woody vegetation surrounding the crops. Of the total PS captures, 22.83% tested positive for XF, while 12.24% of NC specimens also tested positive for XF. Phytoplasma detection was also performed on captured Auchenorrhyncha insect species and plants, with all samples testing negative. These results confirm that PS is the main vector of XF on Majorca Island, both in terms of captures and the percentage of positive insects for XF. PS remains infective primarily on wild hosts throughout the summer, making it a difficult target for insecticide treatments on the crops.