‘Candidatus Phytoplasma mali’: the current situation of insect vectors in northwestern Italy

The two acknowledged vectors of ‘Candidatus Phytoplasma mali’ in north-western Italy, the psyllid Cacopsylla melanoneura and the leafhopper Fieberiella florii, have been compared to highlight their role in the apple proliferation epidemiology in relation to their infectivity, transmission efficiency and permanence in apple orchards and in wild vegetation, predominantly hawthorn formations. The early permanence of C. melanoneura on apple trees is characterised by a high population density and a low infectivity rate. On the contrary, F. florii colonizes apple orchards belatedly and the higher infection rate is balanced by a very low population density. Hawthorn plants proved to be a source of inoculum for the phytoplasma as well as a host plant for the two species. Moreover, another psyllid species, Cacopsylla peregrina, known as a typical hawthorn feeder, proved to be positive to ‘Ca. P. mali’.