After pea aphid Acyrthosiphon pisum genome project, hologenome concept was applied to pea aphid and symbioant such as Buchnera aphidicola. Here we screened symbiotic microorganism in four lab strains (two genetically different insecticide susceptible strains, host plant: cucumber and two different host adopted imiacloprid resistance strains, host plants: cucumber and potato) and four field populations (Jeju, Goryeong, Gimjae and Muju, host plant: potato) of cotton aphid based on GS-FLX pyrosequencing which were conducted with universal primer amplified partial fragments of 16S rRNA from total DNA which was extracted from each strain and population. B. aphidicola occupied over 90% of all identified prokaryotic microorganisms which all tested samples. It’s interesting that the ratio of B. aphidicola occupied over 99% in all of the tested lab strains. However, specific enterobacteriaceae occupied six to seven percents of all field populations which closely related endosymbiont of Glycaspis brimblecombei. That means B. aphidicola occupied only 91~92% of all identified prokaryotic microorganisms. Futhermore, other actinobacteridae and bacillaceae also were detected in field populations. The results obtained for these ratios suggested that there has some interaction between symbioant and environment NOT in imidacloprid resistance.