Host plant selection by Philaenus spumarius: using ground covers as trap crops

The recent introduction and settlement of the vector-borne pathogen Xylella fastidiosa in Europe is claiming the development of long-term containment procedures that allow controlling the disease together with a sustainable management of the crops. Nowadays, minimizing vector populations seems to be the better way to contain the disease in time. Adults of P. spumarius are difficult to manage because of their high mobility and polyphagy, thus control measures should focus on the more sedentary juvenile instars together with the egg phase. This study aims to search for host plant species that could act as trap or repellent plants for nymphs of P. spumarius that could be used as cover crops. Furthermore, the plants should be selected on the basis of P. spumarius oviposition preference. Firstly, choice and non-choice assays were conducted under semi-field conditions to assess the effect of selected plant species on the preference and mortality of P. spumarius nymphs. Ten plant species, belonging to five botanical families commonly used in the ground cover of olive and other X. fastidiosa susceptible woody crops, were selected. Our results suggest that Diplotaxis tenuifolia (Brassicaceae) could be used to repel the nymphs whilst Sinapis alba (Brassicaceae) can act as a trap crop according to the mortality and the colonization rate obtained. By contrast, Taraxacum officinale (Asteraceae) showed one of the highest colonization rate together with a low mortality of the nymphs. Considering these results, a second-choice assay was conducted to study the oviposition preference of P. spumarius females. The results showed that T. officinale and Sonchus oleraceus were the preferred hosts for oviposition of P. spumarius. Thus, these two plant species should be avoided as part of ground covers to be used in olive groves and other X. fastidiosa-susceptible crops.