Looking at Beneficial Insects in the Organic Garden

Insects that prey on or parasitize insect pests (the bad guys) are called beneficial insects. Whether you know it or not, you rely on these allies to help keep the general insect population from from tipping too far toward the destructive side. If you familiarize yourself with these good guys, you can encourage their presence in the garden and avoid killing these innocent bystanders just because they happen to be the insects you spy on your favorite dahlias. You can also buy many of these beneficial insects from mail-order catalogs to increase your local populations.

The average square yard of garden contains over a thousand insects. For the most part, that's a good thing. Some pollinate plants, some help break down organic matter, and some prey on other more damaging pests. Most of the insects in your gardens help — not hurt — your plants. Only a small fraction cause much damage.

Here's a sampling of beneficial insects to encourage in your organic garden:

• Beneficial nematodes: If you're looking for one predator that's worth inviting over for dinner (its dinner, that is), seek no further than beneficial nematodes. These tiny, worm-like creatures live in the soil and are effective against the scourge of many gardens — Japanese beetles. The nematodes prey on the grubs, the larval stage of the beetle, as well as on armyworms, cutworms, onion maggots, raspberry cane borers, and sod webworms. The nematodes (available by mail order) should be mixed with water and applied to your lawn and garden soil. Beneficial nematodes are most effective in moist soil and at soil temperatures between 60 degrees and 90 degrees. They can be killed by exposure to the sun, so they're best applied in early evening or on cloudy or rainy days when the soil temperature is at least 55 degrees.

• Big-eyed bug: These fast-moving, 1/8- to 1/4-inch bugs have tiny black spots on their heads and the middle part of their bodies, as shown in Figure 1. They resemble the pesky tarnished plant bugs, which are a favorite food of the big-eyes. They also dine on aphids, leafhoppers, spider mites, and some small caterpillars. Because these bugs aren't commercially available, look for them on nearby weeds, such as goldenrod or pigweed, and relocate them to your garden.

• Braconid wasps: Several species of braconid wasps, shown in Figure 2, parasitize pest insects. Both the slender adults and tiny, cream-colored grubs feed on a range of pests, including aphids, cabbageworms, codling moths, and corn borers. Purchase these 1/10- to 1/2-inch wasps from suppliers and plant some parsley-family flowers to help keep them around. Adults require carbohydrate food, such as the honeydew secreted by aphids, tree sap ooze, or flower nectar.

• Centipedes: Indoors and out, multi-legged centipedes feed on many insect pests. Most species don't bother humans (unless you count the screech with which they are frequently greeted), and while some southwestern species do inflict a temporarily painful bite, none is dangerous. You can't do much to encourage their presence, but if you can leave them alone to do their job, you'll have fewer insects around.

• Ground beetles: Many beetle species live in or on the soil where both their larval and adult stages capture and eat harmful insects. They vary in color — black, green, bronze — and in size. While most live close to the ground, feeding on aphids, caterpillars, fruit flies, mites, and slugs, the 1-inch-long caterpillar hunter climbs trees to feed on gypsy moths and other tree-dwelling caterpillars. Because these beetles aren't available commercially, the best thing you can do to encourage their presence is avoid using herbicides and insecticides and learn to distinguish them from other unwanted insects. Ground beetles bear an unfortunate likeness to cockroaches, but the latter have longer antennae and a different overall shape. Most of the helpful ground beetles are large, dark, and fast moving. The often have nasty-looking mandibles and eyes on or near the fronts of their heads.

• Hover flies: These insects get their name from the adults' habit of hovering around flowers. The adults, resembling yellow jackets, are important pollinators, while the brownish or greenish caterpillar-like larvae have an appetite for aphids, beetles, caterpillars, sawflies, and thrips. If you grow an abundance of flowers, you're likely to see hover flies.

• Ichneumonid wasps: Ichneumonid wasps, introduced into the United States to control the European corn borer during the 1930s, are a valuable ally in controlling many caterpillars and other destructive larvae. The dark-colored adult wasps (see Figure 3) vary in size from less than 1 inch to 1-1/2 inches, and they have long antennae and long egg-laying appendages — called ovipositors — that are easily mistaken for stingers. The adults need a steady source of nectar-bearing flowers to survive.

• Lacewings: The delicate, green or brown bodies and transparent wings of these 1/2- to 3/4-inch insects, shown in Figure 8-4, are easily recognized in the garden. Adults live on nectar, while the spindle-shaped, alligator-like, yellowish or brownish larvae feed on a wide variety of soft-bodied pests, such as aphids, scale, thrips, caterpillars, and spider mites. The distinctive, pale green oval eggs each sit at the end of its own long, thin stalk on the undersides of leaves. You can purchase lacewings as eggs, larvae, and adults. To keep the welcome mat out for the adults, allow some weeds to flower nearby.

• Lady beetles: You may be surprised to learn that not all lady beetles (also called ladybugs) are beneficial — the damaging Mexican bean beetle is a type of lady beetle! The convergent lady beetle, however, is what most people think of when they praise lady beetles' appetite for aphids. (This species is distinguished from her pest cousin by two converging white lines on its thorax — the segment between the head and the abdomen. The number of spots varies widely.) Both adults and larvae prey on soft-bodied pests, including mealybugs and spider mites. The convergent lady beetle larvae look like small black, segmented pillbugs with rows of knobby or hairy projections and four orange spots on their backs. Although lady beetles are commonly purchased and released into the garden, they often do like the song says and "Fly away home." You can help keep them around by setting out another food source, such as an artificial yeast/sugar or honeydew mixture, which is commercially available from lady beetle suppliers.

• Predatory mites: Similar in appearance to pest mites, such as the two-spotted spider mite, predatory mites are tiny (smaller than 1/25-inch) and quick. They feed primarily on thrips and pest mites and are widely used to control these insects in commercial orchards and vineyards. They are available to home gardeners.

• Soldier beetles: The favorite diet of both adults and larvae of these common beetles consists of aphids, caterpillars, corn rootworms, cucumber beetles, and grasshopper eggs. The adults, shown in Figure 5, are slender, flattened, 1/3- to 1/2-inch long. The larvae have the same shape and are covered with hairs. They spend much of their life cycle in the soil, so they will be more prevalent in areas where the soil is undisturbed.

• Spiders: All spiders are predators, ridding the garden of many common pests. You can provide good habitat for spiders by mulching with hay and straw, which has been found to reduce insect damage by 70 percent due solely to the numbers of resident spiders.

• Tachinid flies: These large flies feed on tent caterpillars, armyworms, corn borers, cutworms, stinkbugs, and other pests. The adult fly is about the size of a housefly and may hover above squash plants in search of prey. It has a bright orange abdomen, black head and thorax, and a fringe of short black hairs on the hind legs. Coriander, coyote brush, evergreen euonymus, fennel, goldenrod, and white sweet clover attract these flies to your yard.

• Trichogramma wasps: Tiny as a pencil point, these parasitic wasps inject their eggs inside the eggs of more than 200 species of moths, such as cabbageworms, codling moths, corn earworms, and cutworms. Their developing larvae consume the host. Buy these wasps commercially and release them during their hosts' peak egg-laying times. Suppliers can give you more specific directions on release times.

• Yellow jackets: It's hard to think of these annoying insects as beneficial, but they do help rid your garden of flies, caterpillars, grasshoppers, and many larvae by taking them home to their young. Yellow jackets are fond of white sweet clover and ivy, so expect to see them near your house if you have either nearby.

Avoid using broad-spectrum insecticides, which kill a wide range of insects, including beneficials. Even some organic insecticides, such as pyrethrin and rotenone, are toxic to beneficials. Often, beneficials are even more susceptible to the insecticide than pests because, as predators and parasites, they must move quickly over leaf surfaces and thus they come into contact with insecticides more readily. Many insecticides are also toxic to bees. If you must use a chemical as a last resort, spray only in the evening when bees have returned to the hive.