Population dynamics of Cacopsylla melanoneura (Hemiptera: Psyllidae) in northeast Italy and its role in the apple proliferation epidemiology in apple orchards.

In the current study, incidence of 'Candidatus Phytoplasma mali' in an experimental apple orchard in northeast Italy, in addition to abundance and phytoplasma infectivity of Cacopsylla melanoneura (Förster) (Hemiptera: Psyllidae) was determined and the role of this psyllid as a vector of 'Ca. P. mali' in this region was reviewed. Insect samples collected in the orchard by the beating method indicated high abundance of C. melanoneura (up to 7.92 specimens/branch); however, the psyllid C. picta was not observed. Molecular analyses revealed presence of 'Ca. P. mali' in 6.25% of overwintered psyllids. This infection rate is quite high in comparison to other localities where C. melanoneura is known as the main vector of the phytoplasma. This finding supports the assumption that C. melanoneura also is paramount in the epidemiology of the apple proliferation disease also in northeast Italy. Moreover, we correlated immigration dynamics to the temperatures registered in the apple orchard, and defined an immigration index to predict the progressive arrival of the overwintered adults from winter sites. Psyllids start to reach the apple orchards when either the average of the maximum temperature of the 7 d is above 9.5 degrees C or the immigration index has a positive value. This index will be a useful tool for the growers to prevent apple proliferation phytoplasma spread with well-timed insecticide treatments targeted against C. melanoneura. However, further research is needed to validate or adjust the index to other apple growing regions, which may affect more efficacious management of this disease and psyllid vector.