Source(s): Jack Arnott

Aphids (plant lice) are small (1/8″), soft-bodied insects that can be many colors with pale yellow or green being the most common. Most are not winged but there may be some winged adults. There are many species of aphids. Some of the aphids, woolly aphids, are covered with white, waxy threads.


Generally aphids are found in aggregations on tender new growth. They are fairly sedentary and don’t move much unless disturbed. Aphids have needle-like piercing/sucking mouthparts. These are inserted into the plant and sap is withdrawn. They suck in more than they can use. The excess comes out the two cornicles, (which look like tailpipes) on the abdomen and is often called honeydew. Honeydew is a sugary protein substance that may be fed upon by other insects such as ants. Honeydew that isn’t taken by the ants drops to the leaf surface and serves as a medium for the development of fungus such as sooty mold. Sooty mold can coat the leaf and reduce its food making ability.

Aphid females generally reproduce asexually producing more females. The adults live about three weeks and can produce large numbers in a short time. Males usually produced prior to winter then mating occurs and the eggs are laid to overwinter under bark or bud scales. Large numbers of aphids can reduce the plant vigor; however the loss of sap generally does not pose a serious threat to healthy, established plants, trees and shrubs. While feeding, aphids inject saliva into the plant. Some aphids do little damage, while the saliva others causes curled or distorted growth or transmit plant viruses.

CONTROL: Before resorting to chemical methods check for natural controls at work.

Biological: Many natural enemies are usually present in the yard already. There are several species of ladybugs or ladybird beetles which feed on aphids. Their larvae (young) also eat aphids. Other aphid predators include green lacewings and their larvae (called aphid lions), syrphid fly (hover fly) larvae, predacious stink bugs and assasin bugs, and the praying mantis. Some wasps and fungi parasitize aphids and help control their levels.

 Aphids can be removed by pruning out the affected part of the plant. For a light infestation using a strong spray from the garden hose directed at the aphids can knock them off where they will die if not eaten by predators. If infestation is light, pick them off with your fingers. Maintain good screening on windows to prevent access to houseplants.

Chemical: Some plant species are very sensitive to nitrogen and an outbreak can be triggered by a high nitrogen fertilizer. Use a slow release fertilizer. Options include summer oils, insecticidal soaps, cyfluthrin, imidacloprid or malathion. Spot treat with a pyrethrin based insecticide. These products kill by contact so thorough spray coverage is essential. Read the label carefully before purchase and use. Insure the target pest and plant are on the label. Some insecticides and formulations might burn desirable plants. Indoors use only pesticides that are labeled for control of insects inside. FOLLOW ALL INSTRUCTIONS ON LABEL.

Resource(s): Insect Pests of Ornamental Plants

Center Publication Number: 51