Analysis of published data demonstrated that the process of baculovirus epizootic depends on a set of various factors. The efficiency of the host-parasite interaction depends on the virus biological activity, multiplicity of infection, biological properties and physiological state of the insect, properties of the food plants, and environmental factors. Based on the data obtained by highly sensitive methods of molecular biology, this review summarizes the discussion of the source of viral infection in baculovirus epizootics. These data shed light on the mechanisms underlying the development of epizootic, a relatively underexplored natural phenomenon.