Aphids, which feed solely on amino acid-deficient phloem sap, have developed symbiotic associations with bacteria that provide them with amino acids that are lacking in a plant's phloem. Three soybean aphid populations were screened for the presence of Buchnera aphidicola and three common species of secondary aphid symbionts (Serratia symbiotica, Hamiltonella defensa, and Regiella insecticola). Diagnostic PCR and subsequent DNA sequencing revealed the presence of two species of symbiotic bacteria present in all three soybean aphid populations tested: Buchnera aphidicola and Arsenophonus. Although Buchnera is commonly found in aphids, Arsenophonus is most commonly found in whiteflies, making the soybean aphid unique among aphids that have been previously tested for symbionts.