Hemiptera is a diverse order of hemimetabolous insects.  Members of this group are characterized by unique mouthparts modified to form an articulated beak (rostrum) for piercing and sucking liquid food.  The Sternorrhyncha (aphids, whiteflies, plant lice, scale insects) and Auchenorrhyncha (cicadas, frog hoppers, leaf hoppers, plant hoppers, tree hoppers) feed almost exclusively on plant sap, while the Heteroptera (true bugs) contain many predators as well as plant feeders, scavengers, and parasites.  The Coleorrhyncha (moss bugs), an obscure group from South America, New Zealand, and Australia, probably feed on mosses.

Some of the plant-feeding hemipterans are significant pests, and a number of species act as vectors of viruses, bacteria, and fungi causing plant diseases.