D. Encourage natural predators, parasites and pathogens.
1. Learn to identify the "good guys" that nature provides to help control the pests in your garden. Don't smash every egg case you find or destroy everything that crawls. Mother Nature may be doing a pretty good job of keeping your pest population under control. Buy or borrow a good reference book on insect identification and learn how to use it.
2. Learn the living requirements of these beneficial animals. Provide them with prey, alternate food sources, nesting and hiding places whenever possible. Many beneficials need pollen or nectar during part of their life cycle. To provide this (and thus encourage them to stay around) plant a variety of flowering plants and herbs in the area. Try to have at least one type of plant in bloom at all times. Commercial feeding supplements are available or you can make your own using various combinations of sugar, honey, yeast and water.
3. Provide initial or supplemental populations if nature hasn't already given you enough to do the job. Some of the "good guys" to look for include the following predators and parasites. (C) = Commercially available and (N) = Naturally occurring only.
a) Antlion - (N) (Myrmeleontidae) 1 to 1 1/2 inch long relative of the Lacewings. These insects look like small dark brown damselflies with clubbed antennae and finely veined wings. The adults prefer pollen and nectar or may not eat at all. The plump larvae (also called "Doodle Bugs") build cone-shaped pits in sandy soil to trap their prey. They will eat just about anything that walks on the ground and is small enough to fall into the pit.
b) Assassin Bug - (N) (Reduviidae) 1/2 to 3/8 inches in length. Adults are generally brown or black in color. Their strong forelegs are used to grasp and hold their prey. With a stout "beak" they suck the juices out of their victims, which are usually larvae and other soft-bodied insects. Prey include Aphids, caterpillars, Colorado Potato Beetles, Japanese Beetles, Leafhoppers, Mexican Bean Beetles, etc... Although generally harmless to humans and other larger animals, Assassin Bugs can deliver a painful stab in defense of unwanted handling. They may also cause an allergic reaction in especially susceptible persons. A close relative, the "Blood-sucking Conenose" (no, I'm NOT making this up!), feeds on the blood of mammals and is a vector of the debilitating and sometimes fatal, Chagas' disease.
c) Birds - Many different species of birds will be happy to help you control your insect population. Especially in the spring and early summer when there are hungry young to feed, even normally seed-eating varieties will be looking for bugs. Landscape your area with a diversity of plants to help provide roosts and nesting areas. Keep pets indoors and curious children (and adults!) well hidden. Offer supplemental food when needed and housing and nesting materials if they are not readily available. Keeping water available in a garden pond or bird bath can almost guarantee that many feathered creatures will visit you on a regular basis.
d) Braconid Wasp - (N) (Braconidae) 1/16 to 3/16 inches (small!). The adults can be black, yellow or red in color. They may eat only nectar or drink the body fluids from their prey. The eggs are laid inside the pest or on the surface of the skin. The white, worm-like larvae hatch and burrow into the host's body where they feed upon their hosts from within, weakening and usually killing the pest. The larvae will then pupate either inside the pest or after emergence) and start the cycle again when it emerges as an adult. The white cocoons are commonly seen attached to the outside of caterpillars. Prey include Aphids, beetle larvae, Cabbageworms, Codling Moths, Gypsy Moths, Hornworms, and Tent Caterpillars.
e) Chalcid Wasp - (C) l/40th of an inch - TINY! They lay their eggs in Whitefly larvae, the eggs hatch and the larvae kills its host as it develops. The adults look like flakes of pepper among the Whitefly population.
f) Domestic fowl - Chickens, ducks, geese etc... all do a pretty good job of cleaning pests out of your garden. Unfortunately, some fowl also enjoy eating certain crops so you will have to experiment and see which birds do the best job for you at the least "cost". As a side benefit, they may also provide you with droppings for fertilizer and eggs and/or meat for food. If you don't want a full-time flock, perhaps you can borrow or rent a few birds from a local farm. You may need to check local zoning ordinances.
g) Encarsia Formosa - (C) A tiny parasitic wasp used to effectively control whitefly populations in greenhouses.
h) Fireflies - (N) 1/4 to 3/4 inch. Nocturnal feeders, the adults and larvae eat mites, snails, slugs and miscellaneous insect larvae.
i) Ground Beetles - (N) 1 to 2 inches in length. Usually nocturnal, the adults and larvae feed upon caterpillars, Cutworms, snails, slugs and other soft-bodies insect larvae.
j) Ichneumon Wasp - (N) 1/8 to 3 inches in length and VERY skinny-looking. The adults lay their eggs inside the pest host where the larvae (and sometimes pupae) develop. The host is severely weakened during occupancy and dies when the predator emerges. The usually observed effect is a dry, brittle caterpillar with multiple oval pupal cases attached. They also attack spiders, borers, wood boring larvae and various other insects.
k) Lacewings - (C) 1 inch long pale green or brown delicate-looking insects with lace like wing veins. The adults prefer pollen and nectar, but the larvae are fierce looking creatures (appropriately called "aphid Lions") with voracious appetites. Common prey include Aphids, Corn Earworms, Leafhoppers, Mealybugs, Mites, Scales, Thrips and Whiteflies.
l) Ladybugs (Ladybird Beetles) - (C) 1/4 inch roundish-looking beetle. The adults and larvae both are very effective predators with each individual having the potential of devouring up to 5,000 pests in its life-span. The larvae live on the juices of their victims while the adults simply consume the entire creature. If the adults do not find a fair-sized population to feed upon, they are likely to look for a better deal elsewhere. So try to time their arrival with a high point in your pest population or seriously consider supplemental feeding so that they will at least stay around long enough to lay eggs. Ladybugs particularly like Aphids (for dinner that is!) but they will also eat Chinchbugs, Colorado Potato Beetles, Rootworms, Scales, Spider mites and weevils.