Perhaps because of their remarkable ability to stage year-round population explosions, aphids have earned the nickname "plant lice." As anyone who's ever found a prized houseplant's undersides suddenly crawling with these translucent little pests knows, the name is apt. Getting rid of them on indoor plants can be just as trying as dealing their nickname namesakes.
Aphids are tiny insects with a pear-shaped body. They may be brown, red or black but most are a jadelike green. Adults reproduce asexually, first as wingless females, then as winged males who lay eggs to hatch in spring--or in your house when you bring the plants indoors in the fall. Because female aphids produce live offspring, there is no break between generations. Colonies can grow within days.
Aphids gather in clusters on the undersides of tender new leaves and extract the protein as the plant circulates it to its growing edges. As they suck out the plant's nutrients on one end, they deposit a sticky substance called honeydew containing carbohydrates. Since the plant circulates a bit of protein in a solution of carbohydrate, the aphid has to consume large quantities of carbohydrate--and produce large quantities of honeydew--to get enough protein to survive.
The result of this activity is stunted new growth on the houseplant. This stunting is especially problematic on indoor plants that, because of lower light levels, don't grow as rapidly and can't recuperate as quickly as can plants outdoors. Although aphids may not kill a plant, they can ruin its appearance. They can also produce enough offspring in the closed system of the indoors to infest every growing plant within a short period.
Avoid indoor infestations by pruning plants and re-potting them in new soil before bringing them indoors. Quarantine plants, whether purchased or from your garden, and hose them off with a stream of water in the evening when aphids settle down for the night. Hose the plants off again in the morning before bringing them inside. Don't over-fertilize plants; aphids thrive on plants grown in high-nitrogen soils.
Wash plants with a few drops of dish soap in a gallon of water or use an insecticidal soap that is labeled for indoor use on affected plants. Cover the soil with cardboard or newspaper and invert small plants in soapy water or an insecticidal soap solution. Prune the plant's affected branches, carefully putting each cutting in a plastic bag before going on to the next. If the plant is badly infested, get rid of it to save the rest of your collection.