Chrysomela populi L. (Coleoptera; Chrysomelidae) is one of the most serious pests affecting poplars. Chemical control is the most widely known suppressive method against this pest. This method is not acceptable in urban forests because of their proximity to people. Entomopathogenic organisms are environmentally friendly control agents and suppress the pest populations under natural conditions. In the present study, the occurrence and distribution of a new entomopathogenic protist, a neogregarine, Ophryocystis anatoliensis (Apicomplexa) in C. populi populations and a member of the family Chrysomelidae is presented for the first time. In total, 90 of 2185 C. populi adults and larvae collected from 16 localities during three years (from 2013 to 2015) were found to be infected by this pathogen. Neogregarine infection was observed in 14 of 16 investigated C. populi populations. The infection was variable between the populations and years. These results confirm that the neogregarine pathogen has a high dispersal potential through the C. populi populations and can be an effective natural biological suppressing factor on the pest populations.