Pear Decline is an economically important disease of pear (Pyrus communis), caused by the phytoplasma Candidatus Phytoplasma pyri. The causal agent is listed as a harmful organism (Council Directive 2000/29/EC) and therefore is a subject to legal requirements for the prevention of the introduction and spread. Until now, the pear sucker species C. pyri, C. pyricola and C. pyrisuga are known as vectors of Ca. Phytoplasma pyri. The objective of the present study was to find out, if in a pear orchard in Lower Austria Ca. Phytoplasma pyri can be detected in individuals of Cacopsylla melanoneura which were captured on host plants (P. communis) potentially infected with Ca. Phytoplasma pyri and on not confirmed host plants (Crataegus monogyna), located close to the infested pear plants, as well as in plants of Cr. monogyna at the same experimental site. The occurrence of C. melanoneura on its main and secondary host plants (Cr. monogyna und P. communis) was confirmed by sampling with the beating tray method during the survey period March until June 2011. Ca. Phytoplasma pyri could not be detected in single individuals of C. melanoneura (n = 237) by molecular biological analysis (PCR methods and RFLP). Therefore this species cannot be classified yet as a potential vector of Ca. Phytoplasma pyri. However, in one third of samples of visual asymptotic plants of Cr. monogyna (n = 14), Ca. Phytoplasma pyri was detected for the first time in Austria. Therefore Cr. monogyna represents a potentially new host plant and source of infection of Ca. Phytoplasma pyri.