In the paper are presented entomopathogenic nematodes (EPN) as a vector of bacteria killing insects. Many abiotic and biotic factors influence the survival and the virulence of mentioned organisms. These biological agents of control are used in practice over twenty years. Knowledge about the relationships between EPN-insect-bacteria allow to increase efficacy of treatment used in order to limiting populations of pests. The paper presents a short review of literature data of titled subjects.