European stone fruit yellows (ESFY) is caused by the phytoplasma ‘Candidatus Phytoplasma prunorum’, which is transmitted from plant to plant by insects of the genus Cacopsylla. Better knowledge of vector distribution in the orchards and on wild host plants is crucial for controlling the disease and preventing its spread. Cacopsylla pruni is known as the vector of ESFY. Recently, a second psyllid, Cacopsylla pinihiemata, has been identified as a vector; however, its vectoring capacity for ESFY phytoplasma is still unknown. The objective of this study was to map the distribution of psyllids in Switzerland and to determine the percentage of infested adults. The occurrence of psyllid species was monitored by sweeping techniques, and the percentage of infested adults was analyzed by nested PCR. Psyllid monitoring revealed that C. pruni is present in every Swiss region, with a similar population density in the different locations. In contrast, C. pinihiemata was only captured in Valais (southwest), the main apricot production area. This is probably due to the presence of specific conifers, which are the overwintering hosts for C. pinihiemata. Infested psyllid adults were found in half of the monitored regions. The percentage varied between 1.3 and 18.2% and was not higher in the apricot production area. Surprisingly, in 2013, ESFY infestation was only found in C. pruni and not in C. pinihiemata. However, in 2012, C. pinihiemata was also infested by ‘Ca. P. prunorum’. The capacity of the two psyllids in ESFY vectoring, their importance in ESFY epidemiology and the consequences on ESFY control strategies are discussed.
