First Report of Cacopsylla picta as a Vector of Apple Proliferation Phytoplasma in Germany.

Since 2000, a serious epidemic of apple proliferation (AP) reappeared in southwestern Germany. Molecular analyses revealed that the AP phytoplasma is associated with this disease. Since no curative treatments or resistant cultivars exist, the only means to reduce spread of the disease is the control of the insect vector. Recently, Frisinghelli et al. (1) identified Cacopsylla costalis as a vector of AP phytoplasma in northern Italy. Following this result, transmission trials with C. picta (synonym C. costalis) were conducted in southwestern Germany at Neustadt (Rheinland-Pfalz) and Dossenheim (Baden-Württemberg) since 2001. Overwintering psyllids were captured from March to May in different orchards. Groups of 5 to 30 C. picta were caged for 2 to 4 weeks on apple seedlings or healthy micropropagated plants. Leaf midribs of test plants were sampled 2 to 3 months after inoculation feeding and tested by polymerase chain reaction (PCR) for AP phytoplasma with specific primers AP5/AP4 (2). In 2001, 1 of 10 test plants, and in 2002, 7 of 40 test plants became AP infected. In 2002, one to four C. picta specimens fed on plants which became infected were tested AP phytoplasma positive by PCR while all psyllids recollected from PCR-negative plants were tested negative. Transmission of the AP phytoplasma was successful at both sites. To our knowledge, this is the first report of C. picta as a vector of the AP phytoplasma in Germany. References: (1) C. Frisinghelli et al. J. Phytopathol. 148:425, 2000. (2) W. Jarausch et al. Appl. Environ. Microbiol. 60:2916, 1994.