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 coniferous and deciduous plants.

Effective control is a problem for homeowners.

Aphids constitute a large group of small, soft-bodied insects.

They may measure up to approximately one-quarter-inch in length.

Aphids have piercing-sucking mouthparts that enable them to remove plant fluids from a host.

Aphids can be recognized by their pear-like shape, a pair of cornicles (tube-like structures) at the posterior end of their body, and long antennae.

The cornicles secrete a defensive fluid that warns aphids of predators and other enemies.

Aphids vary in color from green, yellow, red, purple, brown or black.

Their life history is complex.

Enormous populations can build up in a short time.

Aphids generally overwinter as fertilized eggs.

With the approach of spring, the eggs hatch into nymphs, which rapidly mature into wingless females referred to as a “stem mother.”

Each of these aphids is responsible for producing a large colony of aphids.

Stem mothers produce female nymphs without mating.

Successive wingless generations are produced until the aphid colony becomes overcrowded.

When overcrowding occurs, a generation of winged females is produced that will migrate to other host plants.

The winged females are referred to as spring migrants.

Spring migrants continue to produce successive generations until the end of summer, when winged males and females are produced.

The winged females return to the spring host.

These individuals produce females that mate with males of the previous generation.

These mated females lay eggs that overwinter.

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 excrete a sticky, sugar-containing substance 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 photosynthesis.

Honeydew is attractive to ants, flies, hornets and yellow jackets.

It can also ruin the finish on cars, chairs, tables or other objects that are outdoors beneath aphid-infested ornamental plants.

Cultural practices such as proper pruning, fertilizing and watering may play an important role in preventing or suppressing an infestation.

When practical, try washing aphids off an affected host with a strong stream of water.

Beneficial insects play an important role in aphid control.

Adult and larvae lady beetles, lacewings, some flower fly larvae, and tiny parasitic wasps will use aphids as a source of nourishment for the development of their offspring.

Remember, certain insecticide applications will destroy beneficial insects as well as targeted species.

This practice could leave trees and shrubs unprotected if pest populations increase in the future.

The use of insecticides is often the only effective means of managing aphid infestations.

Several registered insecticide formulations are available. However, to avoid damaging other plants, apply the material only to plants that are specified on the label.

Be sure to follow all insecticide label directions.

“Growing Green” is contributed by Lehigh County Extension Office Staff and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613