Many species of aphids or plant lice occur on ornamental trees and shrubs. Certain species feed on foliage, others on twigs and branches, flowers or fruit, and some on roots. Aphids live on several distinct hosts, spending part of their seasonal development on one host and the remainder on another. They feed on both coniferous and deciduous plants. Effective control of aphids has been a problem to homeowners and landscape managers for years. Some of the more common aphids include the green peach aphid, melon aphid, tuliptree aphid, giant bark aphid, white pine aphid, and rose aphid.
Description: Aphids constitute a large group of small, soft-bodied insects. They may measure up to six mm in total length. Aphids have piercing-sucking mouthparts that enable them to remove plant fluids from a host. Aphids generally can be recognized by their pear-like shape, a pair of cornicles (tube-like processes) at the posterior end of their body, and fairly long antennae (Fig. 1). The cornicles secrete a defensive fluid which warns aphids of predators and other enemies. Aphids vary in color from green, yellow, red, purple, brown, or black.
Damage: Aphids are common, persistent, and sometimes key pests of ornamental plants. Most aphids cause damage to host plants by the removal of plant fluid, by the toxic action of their salivary secretions injected during feeding, and by serving as vectors of plant diseases that are harmful to key plants. Feeding by aphids can stunt plant growth, deform leaves and fruit, or cause galls on leaves, stems, and even roots. Many aphids also excrete a sticky, sugar-containing substance from their anus known as “honeydew.” This material will drop onto the leaves, twigs, and fruit of a plant. A black, sooty mold soon begins to grow on this sugar-rich substrate. This mold decreases the aesthetic appearance of the plant, but when abundant, will also reduce the food-making process of a plant known as photosynthesis.
