"Houseplants that have been outside during the summer should be inspected carefully for insects and other pests before bringing them indoors," states David Robson, University of Illinois Extension horticulture educator.

Houseplants spending the warmer months outside frequently attract a variety of pests. While the plant is outdoors, these pests rarely become a major problem because their numbers are kept low by predatory insects and other animals that eat them and by rainstorms that wash them off of the plant.

Once moved indoors, these pests no longer have their natural enemies and weather problems, so they frequently become major problems.

Spider mites are the most common pests brought indoors. These tiny relatives of spiders suck the juices out of the leaves, causing them to turn bronzy and die. They spin fine webbing across leaves and between the leaf and stem; they appear as specks crawling through the webbing or on the leaf underside. Spider mites may be numerous outdoors, but other insects and mites keep them in check by feeding on the harmful mites.

Aphids are soft-bodied insects the size of pinheads that are frequently brought in with your plants. They are commonly green but may be any color. They and their close relatives, the mealybugs, are found on stems and leaves where they feed on plant sap. Mealybugs are about 1/8 of an inch long and are covered with white, waxy strands that make them look like tiny balls of cotton.

Spraying the plant with an insecticidal soap or some pesticides can eliminate spider mites, aphids and mealybugs. When using these pesticides, take the plant outdoors to spray it.

Whether you use these pesticides or the insecticidal soap, treat the plant weekly for at least three weeks. Particularly severe mealybug infestations may require treatments over a two- or three-month period.

Keep plants separated to avoid spreading insect problems between plants. Segregate plants for at least two months.

Severe insect problems may not be noticeable until furnaces are turned on and the air starts drying.