Worldwide potential insect vectors of Xylella fastidiosa and assessment of their importance with a focus on Morocco

In Morocco, the climate conditions are favorable for the establishment and the spread of Xylella fastidiosa (X.f). However, the successful establishment of the bacterium depends on many factors; mainly: bacterial subspecies and sequence type, host plants susceptibility, feeding behavior and transmission efficiency of the insect vectors. Knowledge of the relationship between the bacterium–affected crop agro-ecosystem and potential insect vectors is of crucial importance. In this work, we list the tritrophic interaction X.f-host plants-insect vectors that occur worldwide in order to apply it to the current situation in Morocco and for risk analysis on the bacterium in the country. Two most relevant X.f subspecies of the bacterium (in terms of impact on crops) were considered, namely, subsp. fastidiosa and subsp. pauca. Based on the international literature and public databases, the majority of the X.f-insect vectors are comprised in two families: Cicadellidae and Aphrophoridae. Among all cicadellid species recorded, a high number had the capacity to transmit X.f to hosts in America while this ability is null for other regions (except Graphocephala versuta Say (Hemiptera: Cicadellidae) recorded in Algeria). In Morocco, none of the cicadellid genera reported worldwide as vectors of X.f, have been so far reported, whereas many species of spittlebugs and leafhoppers are present. Philaenus tesselatus Melichar (Hemiptera: Aphrophoridae) is highly abundant in Morocco and could play a role as potential vector in case the bacterium is introduced in the country. With regard to the X.f hosts, citrus, olive, almond and grapevine, forest agroecosystems and oleander are considered the main susceptible species present in Morocco.