Click for larger image Aphids (Hemiptera) are a common problem on indoor plants. Sticky honeydew on leaves is a common first sign that they are present.

Aphids are small, piercing-sucking insects no larger than 1/8 inch. Sometimes called plant lice, they are one of the most common pests of indoor plants. Aphids are easily brought indoors on infested plants, attached to clothing, or by the wind through an open window.

Symptoms and Diagnosis

Aphids come in a range of colors including green, yellow, orange, red, beige, pink, and black. They love young tender growth, which can be completely covered with the insects. They are also frequently found in the center of new shoots or under leaves, which they cause to curl. Aphids exude a sticky honeydew that coats leaves making them sticky and shiny. In moist conditions a black fungus called sooty mold will grow on the honeydew. Sticky leaves are often the first symptom gardeners may notice. Ants may also be attracted to the honeydew.

Life Cycle

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 Strategies

1. Remove concentrations of the insect. Prune off and dispose of plant tips or leaves that are heavily infested with aphids or take plants outdoors and wash off the aphids with a forceful spray of water. In some cases, if caught early, this may eliminate the problem.

2. 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.

3. 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.

4. 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. It is commercially available under the name Margosan-O. Sprays containing pyrethrin, another plant-derived insecticide, are also effective and more benign than other chemical pesticides. Follow label directions and, if possible, spray out-of-doors or in a garage, weather permitting.

5. 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 introducing pests indoors. Bringing plants indoors in the fall is another way of introducing insects indoors.

Organic Strategies

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

More images:

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Aphid (Hemiptera) on citrus (Citrus)
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Aphids (Hemiptera) on citrus (Citrus)
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Aphid (Hemiptera) and cast skin on New Guinea impatiens (Impatiens hawkeri group)
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Winged aphid (Hemiptera) on indoor plant