The Wheat dwarf virus (WDV) is transmitted to cereal by the leafhopper Psammotettix alienus Dahlbom, 1851. It occurrs in two strains, a barley- and a wheat strain. The aim of this study was to increase the knowledge of the ecology and the occurrence of this virus in the middle and the southern parts of Saxony-Anhalt from 1995 to 2002. By means of infected outdoor winter barley an antiserum against WDV was prepared for virus diagnosis. In all years of investigations the WDV has occurred in fields of cereal (partly > 50 %). An early sowing date of winter cereal results in a high infestation of the newly sown cereal in autumn. In years with an epidemiological appearance of BYDVs (1995, 2001, 2002) the WDV occurs in lower range. In reverse, a higher infestation of WDV is accompanied with lower infection rates of BYDVs. In outdoor investigations eleven species of grasses were found as new host species under natural condition of infection: Avena hybrida Peterm., A. sterilis ssp. ludoviciana Dur., Bromus arvensis L., B. commutatus Schrad., B. hordeaceus L., B. japonicus Thunb. ex Murray, B. sterilis L., Deschampsia cespitosa (L.) P. Beauv., Festuca pratensis Huds., Phalaris arundinaceae L., and Setaria italica (L.) P. Beauv. In the area of investigation the barley strain of the WDV was observed predominantly. Each heterologic strain also was detected in individual plants of different species of cereal. Some of the examined species of grasses were found as host of both strains. In perrenial outdoor investigations with different genotypes of maize the suscebtibility of the inbreeding line FAP 1360A against the barley strain of WDV was found. For the first time, investigations of transmission of the barley strain of the WDV were carried out by means of its vector. The examination of the effectivity of the transmission of the virus by developmental stages of P. alienus produced a higher effectivity for the leafhoppers of the younger stages. In view of the modus of transmission remarkable differences between several individuals were shown. The persistance of the virus in the vector came up to 100 days at the most. In spite of virus acquisition apparantly not all leafhoppers of a population serve as vectors. The determination of the time of acquisition by only four leafhoppers, which successfully transmitted, came to 10, 15, and 20 minutes. The time of circulation fluctuated between 24 and 72 hours. In the course of several vegetation periods, the contingents of virus transmitting and viruliferous leafhoppers were determined in an outdoor population by using of a biological test and by PCR. The rate of virus transmitting animals succumbed to annual fluctuations (2000: 37.3 %, 2001: 19.2 %, 2002: 0.8 %). Within one vegetation period, differences with the transmission were noticed likewise. By means of PCR basically the barley strain was established. In individual leafhoppers both strains could be verified. A comparison between the biological test (determination of the virus transmitting animals) and the PCR (determination of the viruliferous animals) resulted in a relatively high agreement (65.0 % and, respectively, 88.8 %). Considering the already known and the own results for the area of investigations, a scheme of the infection cycle of the WDV was developed.