Wu Bei Zi

Wu Bei Zi, the Chinese gallnut, is the dried insect-induced gall formed on the leaves and petioles of the Chinese sumac Rhus chinensis Mill. (Anacardiaceae) by the aphid Melaphis chinensis (Hemiptera, Aphididae). The aphid is host-alternating: its sexual generation parasitizes mosses, while the asexual gall-forming generation feeds on Rhus chinensis, where its saliva induces the plant to produce hollow, irregular, often horn- or fist-shaped outgrowths 3–9 cm long, with thin pale-brown velvety walls enclosing the developing aphid colony. The mature galls are collected in autumn before the winged aphids emerge, scalded to kill the insects, and sun-dried. The walls contain very high concentrations of hydrolyzable tannins (up to 70% gallotannin), the basis of the substance’s extreme astringency. In TCM Wu Bei Zi is sour, astringent, and cold, binding the lung, intestine, and lower jiao to stop chronic cough, diarrhea, sweating, bleeding, and seminal emission; it is also applied externally to sores and ulcers.