Abstract: Worldwide there are insects that transmit diseases and these are a focus of research. In Europe, fruit trees of the family Rosaceae are seriously affected by phytoplasmas of the apple proliferation group. Phytoplasmas are plant pathogens causing a wide variety of symptoms that can often lead to death of infected plants. Jumping plant lice of the genus Cacopsylla are their vectors. It is well known that Cacopsylla use chemical cues for orientation and host identification. To overcome the spread of these diseases, especially the transition from infected to healthy plants, several techniques using volatile substances for attracting or repelling vector insects are being studied. In this study, we started to screen possible repellent substances like eugenol to repel Cacopsylla pyri, the pear sucker. Secondly, we begun to evaluate the preferences of C. pyri for leaf colors from symptomatic and non-symptomatic pear plants, and to determine the relative effect of their spectral reflectance parameters for host finding.