Tetraneura ulmi, commonly known as the elm leaf-curl aphid, is a small insect belonging to the family Aphididae. It is a specialized aphid species that infests elm trees, causing the leaves to curl and distort. These aphids have a yellowish-green body with black markings and are typically found in colonies on the undersides of elm leaves. They feed on the sap of the tree, which can weaken the host plant and potentially lead to leaf drop.