American leafhopper Scaphoideus titanus Ball. is a new pest in Croatia that indirectly endanger the cultivation of grapes. In Croatia pest has been first reported in 1987. Damages caused by the american leafhopper are mainly related to the transfer of phytoplasma, the causal agent of Flavescence dorée, disease belonging to the group generically termed as grapevine yellows. In the European vineyards most common phytoplasmas are Flavescence dorée and Bois noir. Once infected, grapevines stay permanently ill, without possibility for curative suppression of the causal agent.. Consequently, measurements of prevention such as suppression of the vector are needed. American leafhopper has been found in many European countries, and is present in almost whole territory of the Republic of Croatia, except in Central Dalmatia. The lifecycle of these species is still not well known, especially under the different climatic conditions present across the Europe. It is not known if there is a difference in the preferences of pests to the grapevine of different health status, neither if the health status of a plant has any effect on the duration of pest development. Therefore, the study was conducted in which the differences in the duration of the development and mortality of the american leafhopper on the leaves of grapevines of different health status, as well as the preferences of american leafhopper towards healthy or infected leaves, were determined. By the cultivation of different developmental stages of american leafhopper on healthy and infected grapevine leaves under controlled conditions, the differences in the duration of development and mortality were determined. American leafhopper has a shorter development on healthy leaves and increased mortality in the infected leaves. It was found that the larvae and adult forms of american leafhopper have different preferences to healthy and phytoplasma infected leaves. Larvae prefer more healthy leaves while diferences were not observed in adults forms.. These results could help in understanding the behavior of pest and development of new tools useful in monitoring and control.