The article is devoted to the study of the species composition of microorganisms of the trophic chain: cereal plants – aphids. The objectives of the study were to determine the species composition, occurrence index and quantitative indicators of associative microorganisms of rye plants of the “Marusenka” variety and common grass aphids. The work was carried out on the basis of the Department of Microbiology and Plant Physiology of N. G. Chernyshevsky SSU.