Which insect is associated with Buchnera aphidicola as its obligate endosymbiont?

• A. Bees
• B. Aphids
• C. Butterflies
• D. Flies

Answer: (B)

Aphids form a classic example of an obligate endosymbiosis with Buchnera aphidicola. Their diet—plant phloem sap—is rich in sugars but deficient in several essential amino acids. Buchnera lives inside specialized insect cells called bacteriocytes and continually synthesizes those missing amino acids, supplying the aphid with nutrients it cannot obtain from its food. This mutual dependence is so strong that the two have coevolved together, with Buchnera transmitted from mother to offspring and undergoing genome reduction as it becomes more specialized to the host’s needs. That tight, nutritionally essential partnership is why aphids are the insects associated with Buchnera as their obligate endosymbiont. Other insects have different symbionts or gut microbiota that support their biology, not Buchnera.