The planthopper Pentastiridius leporinus (L.) (Hemiptera: Cixiidae) has been identified as the main vector of ‘Candidatus Arsenophonus phytopathogenicus’, a plant pathogenic bacterium associated to a sugar beet disease in eastern France called syndrome ‘basses richesses’. In a 2-yr survey (2006–07), we quantified the abundance of P. leporinus populations migrating into 29 sugar beet fields in eastern France. Sticky traps posted in these fields were monitored on a twice-weekly (2006) or weekly (2007) basis. Subsets of the captured planthoppers were tested for the presence of Ca. A. phytopathogenicus through polymerase chain reaction (PCR). Our results showed that planthoppers colonized sugar beet fields in June and July of each year, following temporal patterns of migration that were fitted to logistic functions. The number of planthoppers migrating into sugar beet fields greatly varied among the fields and the years surveyed, averaging from a few (2–10) to over 400 planthoppers per trap. Interestingly, the prevalence of planthoppers infected by Ca. A. phytopathogenicus increased nonlinearly with the abundance of planthoppers captured on the traps. The proportion of infection for Ca. A. phytopathogenicus ranged from ≈0.07–1 (total infection) in small (2–10 planthoppers per trap) and large (400 planthoppers per trap) populations, respectively. We hypothesize that the outbreaks of P. leporinus in sugar beet fields, and the consequent increased rates of planthoppers infected by the Ca. A. phytopathogenicus, are key factors leading to the emergence of the sugar beet disease in eastern France.