Aphids (Hemiptera) are small, piercing-sucking insects no larger than 1/8 inch. They are a very large and diverse group of insects that plague the garden, especially during the beginning and end of the growing season. At least 4,000 aphid species have been identified; variations in color, size, and appearance make it impossible to generalize. They are very common in the spring on the tender, new growth of outdoor plants, and can be brought indoors through infested plants, attached to clothing, or through an open window.  

Symptoms and Diagnosis 

These small, soft-bodied, pear-shaped insects suck the juices from leaves and stems. The foliage of infested plants will show pale or yellow spots. Whole leaves may turn yellow or brown or may be curled, puckered, or stunted. Flower buds may be seriously damaged and the blossoms distorted. Check for clusters of these common pests on the underside of leaves or clustered on new buds, tender stems, and young leaves, especially during the springtime. Aphids multiply more rapidly with high nitrogen levels. Another sign to look for is a sooty black layer on the leaves. Because aphids suck more plant sap than they can use, they exude honeydew onto leaf surfaces. Ants may be found feeding on the honeydew before it molds. 

Life Cycle 

Females lay eggs toward the end of the growing season in the bark or bud scales of their favorite plant. When the eggs hatch the following spring, the nymphs are all female and are called "stem mothers". These females will give live birth to daughters without mating. Toward the end of the growing season, males are produced, mating occurs, and the eggs will again overwinter in the plant material. 

In indoor conditions most aphids do not lay eggs; the adult females are capable of giving birth to young without mating. Since a female can produce young at the rate of 3–6 per day for several weeks, populations can increase rapidly. The young look like the adults and begin feeding right after birth. They shed their skins (molt) approximately four times before they are mature adults. The shed skins are good indicators that damage was done by aphids when the live insects are no longer present. 

Integrated Pest Management (IPM) Strategies  

1. Remove concentrations of the insect. Prune off and dispose of plant tips or leaves that are heavily infested with aphids. Spray heavy concentrations with a forceful stream of water to dislodge pests 

2. Through good horticultural practices, aphids can be minimized. One step is to control the amount of nitrogen added to the garden. By using slow-release fertilizers such as ammonium or urea-based fertilizers, compost, decomposed manure, fish emulsion, or liquid seaweed, you slow the rate at which the aphids can reproduce. Another step is to prune moderately in winter and early spring, saving the heavy pruning for the mid-growing season. This prevents the aphids from destroying fresh growth in early spring. 

3. To limit future problems, inspect plants regularly. With regular inspection pest problems can be caught when just beginning and control is easier. It is also recommended to isolate newly acquired plants for 2–3 weeks to limit the introduction of pests indoors. Bringing houseplants indoors in the fall is another way of introducing insects indoors. 

4. Use insecticidal soap. Insecticidal soaps specially formulated to kill insects and not damage plants are effective if used frequently until the problem is under control. Keep in mind it will kill beneficial insects as well as aphids 

5.  Use superior horticultural oil sprays. Highly refined oils sold as superior or horticultural oils are also very effective in controlling aphids. The oil suffocates the insects. Unlike dormant oils, these oils are highly refined and under proper conditions, can be applied to plants in foliage without damage. Follow label directions to avoid damage to some plants that may be sensitive. Superior oils are also considered nontoxic and are less likely to harm beneficial insects. When spraying indoors, protect surfaces that may be damaged by an oil residue. 

6.  Use chemical insecticides. Many insecticides registered for use indoors are available. A very safe product made from the seeds of a tropical tree is Neem. Sprays containing pyrethrin, another plant-derived insecticide, are also effective and more benign than other chemical pesticides. Follow label directions and, if possible, spray outdoors weather permitting. Pesticides registered for use include carbaryl (Sevin), disulfoton (Disyston), malathion, bifenthrin, imidacloprid, and permethrin. 

7. Encourage beneficial insects in your garden. Many beneficial insects feed on aphids, including green lacewings, ladybugs, aphid midges, and braconid or chalcid wasps. These are all available commercially. Prevent future infestations with a thorough cleanup of your flower beds in the fall. This can eliminate aphid eggs that may overwinter on leaf litter or twigs of trees and shrubs. 

Organic Strategies

Strategies 1, 2, 3, and 7 are strictly organic approaches. For an organic approach to Strategies 4, 5, and 6 consult the Organic Materials Review Institute (OMRI™) for appropriate insecticidal soap and pesticide products.

Pesticide Disclaimer: 

Always follow the product's label and ensure the product is effective against aphids. Not following the pesticide label before usage is a violation of federal law.