The article contains information about ecologic problems in agriculture and relationships between harmful and useful organisms in agro ecosystems. For the purpose of developing biological plant protection measures, relationships between crop plants and insect pests are investigated. It examines the role of Dr. Mircea Ciuhrii in defining the mechanisms of interaction of crop plants with harmful organisms on the one hand and their use with useful organisms. Establishing relationships between harmful and useful organisms have been the basis for the development of biological methods of plant protection, especially the application of useful microorganisms in the formulation of biological preparations. This allowed the development of technological processes for the production and application of entomophages, sex pheromones and other environmentally friendly means of plant protection. The main achievements of Dr. M.Ciuhrii are set. This demonstrates the amazing capacities and virtues of the scientist in promoting the biological protection of plants.