Colored objects and sticky traps. A number of groups of insects are attracted to specific colors, and colored objects have been used to develop trapping devices for collecting insects and monitoring their populations. Horse and deer flies, for example, are attracted to shiny black objects such as beach balls (see Malaise traps). These are used to increase attract these species to canopy or malaise traps. Yellow is attractive to many insects commonly found in gardens or greenhouses, including winged adult white flies, aphids (see Yellow pan traps, below), leaf miner flies, fungus gnats and thrips (which are also reportedly attracted to blue). Colored cards or other objects such as plastic disposable drinking cups coated with a sticky substance like Tanglefoot® (avaliable in spray or gel formulations) make excellent traps to collect and monitor populations of these insects.
Yellow pan traps (with salt water). Shallow trays, generally painted yellow on the inner surfaces and filled with a fluid such as salt water, can be used to attract and trap small flying insects such as winged aphids. These can be used both as a collection device and an indirect method to sample population levels of insects attracted (also see Pitfall traps).