Insects can come from outdoors or other plants. Flying stages, airborne eggs or brushing an infected plant exposes other plants. The best defense against insects is to keep your plants healthy.

Check your plants often to find insects early; pay particular attention to the backs of leaves, and internodes. If an insect population is found, wash thoroughly with warm water and a mild dish washing liquid and rinse foliage thoroughly, twice a week for 2-3 weeks.
If insecticide is necessary, call your local garden center for recommendations. Make sure that plants are moist before application. Always read the instructions before applying any chemical. You may wish to take a pro-active approach and thoroughly wash your plants regularly as well as washing any new plants.
At Plantscape Designs Inc Boston, Ma we always either replace the infected plants with a new one or use harmless biological predators or parasites to totally and safely irradiate your indoor office plants or insect pests.