Traps and Barriers
Yellow Flypaper: Old-fashioned fly-paper is very effective in the garden for aphids and whiteflies. In fact, any board or heavy paper painted yellow and coated with a sticky substance such as tanglefoot (available at garden centers) will do the job.

Pheremones: These biological mating scents attract insects to a trap which is coated with a sticky substance. Pheremone traps are effective, but remember they are "attracting" the insects - be sure to position them on your garden perimeter or you'll attract outside pests into your garden! Available at larger garden centers, usually in the $5 - $15 range.

Floating Row Covers: Floating row covers consist of lightweight opaque material which is draped over the garden bed. Sunlight and water go through, but insects and birds are kept out. The material is so light that the growing plants simply push it up as they grow - like Jiffy Pop popcorn. The edges of the row cover need to be anchored with rocks or boards or the wind will lift it. The material is "spun" which resists tearing, but usually begins to break down after a few years. Row cover material comes in rolls so you can make a continuous cover no matter how long the garden bed.

Row covers are great for protecting seedlings. They are even more useful throughout the growing season when placed over vegetables such as carrots, beets, broccoli, swiss chard and spinach because it makes an effective barrier against flying insects looking for these plants to lay their eggs on.

Cloche: The cloche is like a miniature greenhouse for your seedbeds and young plants, and acts as a barrier against pests. Unlike the floating row cover, however, the cloche has to be opened on hot days and for watering, and this presents an opportunity for pests to find the plants. But because the cloche helps seedlings and young plants get well established, the enhanced natural resistance of stronger healthy plants is the best defence against pests and disease. Click here for more info or for plans to build your own portable garden cloche.

Barrier Paper: Scraps of waxed cardboard from milk cartons, or a scrap of roofing felt are a simple yet effective defence against cabbage moths. Cabbage moth larva kill young sprouts of the Brassica family (broccoli, cabbage, brussel sprouts, kale or cauliflower).
Cut into 2" squares and slit one side into the center; make another small slit crossways. Open the slit and slide the square so the seedling stem is in the center. This prevents the cabbage moth from laying eggs at the base of the sprouts. Leave in place - as the plant grows it will simply push the slit open wider. Be sure to apply as soon as the sprout appears, or the moth will beat you to it!

http://www.eartheasy.com/grow_nat_pest_cntrl.htm