The chemical free way to both control pests, and monitor their populations. The idea is used widely in professional growing, insects can't resist the lure of bright yellow, and as they land on it the sticky glue sticks them to the surface.
The traps are square-gridded, so you can easily count how many are rapped and see if populations are rising. Use in greenhouses, or conservatories where insects are active. Suitable for organic systems.