Preliminary studies about the effect of Candidatus Phytoplasma mali on the psyllid Cacopsylla melanoneura (Homoptera: Psyllidae)

Cacopsylla melanoneura Förster (Homoptera: Psyllidae), a univoltine psyllid, is a vector of ‘Candidatus Phytoplasma mali’, the etiological agent of apple proliferation disease (AP), which is a severe problem in Italian apple orchards. Preliminary studies were conducted about the influence of ‘Ca. Phytoplasma mali’ on the fitness of C. melanoneura. Couples of overwintering adults of the psyllid collected in the field were exposed to the phytoplasma by feeding on infected and non-infected apple (Malus domestica L.) (Rosaceae) shoots. The effect of the exposure to the phytoplasma with the diet was determined by measuring some of the life history traits correlated to the fitness of the individuals such as longevity of the females, number of eggs laid, egg hatching and development of larval instars The longevity of AP-exposed adult females was not significantly different to that of psyllids fed on healthy apple shoots. However, the AP-exposed females laid significantly less eggs than unexposed ones, and the eggs produced by AP-exposed females were significantly delayed in hatching. Moreover, the progeny of AP-exposed females (number of nymphs emerging from eggs laid on apple shoots) was significantly less numerous than the progeny of unexposed females, while there were no significant differences in their development to adulthood. Further studies are necessary to establish whether such differences are due to the presence of AP phytoplasma in the body of the psyllid or in the plant.