Whiteflies can be a serious pest on plants grown indoors. These tiny insects look like miniature white moths and can congregate in large numbers on the undersides of leaves [1] where they suck plant sap. The larvae are particularly damaging to the plant.

Whiteflies are attracted by the color yellow. One easy way to control them is to put out yellow cards covered with a sticky substance [2]. You can buy such commercial traps, but the sticky substance on these tends to dry out quickly and then the card is no longer effective.

To make a re-useable trap take an old pane of glass and spray one side with bright yellow paint [3]. When the paint is dry, spread a very thin coat of motor oil on the unpainted side. Now place the piece of glass with the oil side up near infested plants. The Whiteflies attracted by the yellow color will get stuck in the oil. Every month or so, wipe the glass clean and apply a fresh coat of oil.