Studies on the competence of potential Xylella fastidiosa vectors in the Balearic Islands (Spain)

Since Xylella fastidiosa (Xf) was first detected in Majorca (Balearic Islands) in October 2016, four sequence types (ST) have been described in the Balearic Islands infecting 28 host species. Xf subsp. multiplex (ST 81) is found in Majorca and Minorca and Xf subsp. pauca (ST 80) in Ibiza, whereas Xf subspecies  fastidiosa (ST 1) and Xf multiplex (ST7) are only present in Majorca. The bacterium is naturally transmitted by xylem “specialist” insects belonging to the suborder Auchenorrhyncha (Hemiptera). In Italy, Philaenus spumarius (Hemiptera: Aphrophoridae) has been described as main vector of CoDiRO strain (Xf subsp. pauca) in olive orchards, even though recently P. italosignus and Neophilaenus campestris have also been shown to transmit Xf . Studies performed in different orchards from the Balearic Islands revealed that P. spumarius together with N. campestris were the most abundant Aphrophoridae species, being the main candidates for Xf transmission. Transmission tests with P. spumarius and N. campestris were performed to determine the capacity of local populations to transmit Xf subspecies under semi-field conditions (greenhouse). Xf subsp. fastidiosa was transmitted to healthy vines by infected P. spumarius that previously had fed on infected vines and from almond to  almond. On the other hand, in crossed-transmission tests P. spumarius was able to transmit Xf subsp. fastidiosa from infected almonds to healthy grapevines and from infected grapevines to almond, and Xf subsp multiplex from wild olive tree to almond trees. Preliminary research has shown that N. campestris can transmit Xf subsp fastidiosa vine to vine.