Pea Aphid

The pea aphid (Acyrthosiphon pisum) is a small sap-sucking insect that attacks peas, alfalfa and clover. It is a model for studying symbiosis, since it depends on bacteria that supply nutrients missing from sap.

🧬 Field Guide Specimen: Open Pea Aphid in the CRV Science Field Guide to log the specimen, see its place among the Ecdysozoa lineages in the Cladogram Explorer, and test your recall in the Red List conservation game.

In summer, wingless females give birth to live clones, and each newborn already contains developing embryos of the next generation. This telescoping of generations lets populations explode. When crowded or when autumn approaches, females produce winged offspring or sexual forms.

Plant sap lacks several amino acids that animals cannot make. Aphids house the bacterium Buchnera aphidicola in special cells (bacteriocytes) and the bacteria synthesize the missing nutrients. The partnership has lasted more than 100 million years. See Bacteria.

Red and green pea aphids owe their pigments (carotenoids) to genes that appear to have been acquired from fungi by horizontal gene transfer, an unusual case of an animal making its own carotenoids. See Horizontal gene transfer.

• Horizontal gene transfer — fungal genes in aphids
• Bacteria — obligate symbionts
• Wolbachia — another insect endosymbiont