Feeding penetration of mid- and lateral veins of pecan leaflets by Monellia caryella (Fitch) destroyed the epidermis and rib parenchyma, and abaxial phloem cells at the feeding site were lacerated. The feeding position of the aphid (nearly parallel to the host vein) derives from the geometry of the 215 μ stylet that is barely long enough to reach the required feeding location in the phloem and from the fact that the stylet will flex laterally but not posteriorly or anteriorly. The damage done by Monelliopsis nigropunctata (Granovsky) to cells at the feeding site, at the junction of veins of the coarse vascular network with larger veins, was similar to the damage done by M. caryella. In addition, prolonged feeding by M. nigropunctata caused the cells of the rib parenchyma, fibrous sclerenchyma, and the abaxial phloem to become internally homogeneous with loss of cell integrity. When very heavy damage occurred, chlorosis was observed. Melanocallies caryaefoliae (Davis) fed intercellularly in the smallest phloem-containing veins of the fine vascular network and destroyed the chloroplasts of the mesophyll for 5 to 6 mm around the feeding site. All 3 species fed primarily in the phloem.