Houseplants are like people. When they become weak or under stress, they get sick and require a "doctor's" care. Preventative measures will reduce the amount of insects your plant will acquire.
Plants should be chosen to suit the conditions in your home, thereby decreasing stress right from your initial purchase. Through proper care, plants will remain strong and able to fight off some, if not all, infestations and infections. By over watering or under watering, plants will be easy prey for hungry insects. Temperature is also a factor in your plants' health and susceptibility. In the winter months, the air has a tendency to be dry and these are perfect conditions for insects to thrive. To reduce hot, dry conditions around your plants, place a tray filled with pebbles and water under your plants. The water should not touch the bottom of the pots. Evaporation from these trays will create a cooler, humid atmosphere.
Plants may also be confused by air conditioning, as their temperature and light combinations are mixed up. The plant is, again, stressed. When it's cool, a plant is programmed to be dormant, but the light is high in summer so the plant wants to grow but not to its optimum level. It is warm in winter, so plants grow quickly but there isn't strong light; therefore, the growth is spindly. Plants prefer a cooler night temperature than day temperature to grow most vigorously.
Insects get into your home in a variety of ways. They may have come in on a pet or yourself brushing up against an infected plant elsewhere. New plants introduced to the area may have brought them in. Your plants may even have already had the insects, but the symptoms were not noticed until new plants showed signs. Plants will also pick up any insects if left outdoors for the summer. Be sure to spray two or three times at seven to 10 day intervals before bringing them back indoors, or be sure to give them a good check-up. High light plants tend to be more susceptible as their conditions for optimal growth mirror that of the insects. Unless an unhealthy plant is nearby or it is the winter season, low light plants are less likely to get insects. All the conditions above will influence your plants' immunity to fungi and diseases as well.
Aphids have fat, fleshy bodies that are either green or yellow. They may cause severe distortion or stunting and are good plant disease vectors. They also drop the sticky sap called honeydew onto the leaves. Wash off with stream of water, Safers Soap or ladybugs are possible cures.
Organic controls will also work, search online for recommendations, but Safer's Soap, drenches with tea or nicotine are examples of organic cures.
As you can see, there are many types of insects that can affect your houseplants. Most are not immediately noticeable to the untrained eye, so there may be a lot of damage before you detect it. Try to be aware of any abnormalities in your plants, and be a good researcher before buying your plant material.