Detection of 'Candidatus Phytoplasma mali' in different populations of Cacopsylla melanoneura in Italy

Cacospylla melanoneura Förster (Hemiptera Psyllidae) is one of the vectors of 'Candidatus Phytoplasma mali', which is the causal agent of apple proliferation (AP) disease. In 2006 and 2007, overwintering adult psyllids were collected from different host plants (apple, hawthorn and conifers) in different localities to assess the natural infection of C. melanoneura. AP phytoplasma was detected in insects through the use of PCR amplification with specific primers (AP3/AP4). Eleven percent of the psyllids collected from apple in the Trentino region were infected with AP phytoplasma, as compared with 18.63% of the psyllids collected from apple in the Aosta Valley and none of the psyllids collected from apple in the Veneto region. The percentage of AP-positive overwintering adults was higher in the Aosta Valley than in the Trentino region. Furthermore, considering the level of AP presence in the monitored orchards, a positive correlation between the infection rates in the insects and the percentage of symptomatic plants was observed. Regarding psyllids collected from hawthorn, only few individuals tested positive in Trentino populations, while higher infection levels were found out in the Aosta Valley. Interesting percentages of positive psyllids resulted also in the insects collected from conifers (10.5%). Data obtained in this work demonstrate therefore that 'Ca. P. mali' may overwinter in the body of C. melanoneura and that there are differences in the infection proportion among populations.