Beneficial Insects in the Garden

Beneficial insects, which are those that feed on or parasitize garden pest insects, include bees, lady beetles ('lady bugs'), lacewings, stink bugs, assassin bug, hover flies, paper wasps, bald-faced hornet, beneficial nematodes, centipede, dragonfly, ground beetle, parasitic wasps, and spiders.

Assassin bugs are voracious predators of many garden pests including flies, mosquitoes, beetles and large caterpillars.

Bald-faced hornets eat many pests including crane flies and other flies. They also eat yellow jackets. They may also act as pollinators of some plants. If the nest is disturbed, these hornets will sting humans.

Beneficial nematodes are effective in controlling cranefly larvae, flea larvae, and root weevils. Bees are pollinators of a variety of plants.

Centipedes prey on pests and insects in the soil including slugs, worms and fly pupae. Centipedes kill their prey with venom, and their bite is moderately painful (although not dangerous) to humans.

Dragonflies (and damselflies) eat mosquitoes, aphids and other pest bugs.

Lacewing larvae and adults feed voraciously upon aphids and other small insects, insect eggs, and spider mites. They also eat leafhopper nymphs, whiteflies and small caterpillars.

Lady beetle larvae and adults feed on soft-bodied insects such as aphids, mealybugs, scale insects and spider mites as well as insect eggs.

Different species of parasitic wasps may attack aphids, whiteflies, and butterflies or moths, such as cabbage loopers and hornworms.

Spiders are the most important predators on insects, killing more than all other predators combined. They feed on a broad variety of pest insects year-round.

Supporting Beneficial Insects

You may kill the insects that are helping you keep pests in check. This means you will have to spray more in the future. Also, insects benefit your garden by pollinating your plants, helping them grow and propagate.

Beneficial insects are more likely to remain if there is a ready food supply. While many of these predators can be purchased, it is probably cheaper and more effective to encourage the ones already in the garden. Many beneficial insects need to sip flower nectar to survive. Plan the garden to feed beneficial insects by choosing a variety of plants that will bloom as many months of the year as possible.

Here are some suggestions for supporting beneficial insect populations:

• Plant nectar-producing flowers to further increase the food supply. Plants in the cabbage, carrot, and sunflower family are especially attractive to beneficial insects.

• Control ants as they may prevent predators from controlling aphids.

• Don't use persistent, broad-spectrum, contact insecticides as they provide only temporary pest control and are likely to kill more of the natural enemies than the pests. When their enemies are gone, pest populations may soar and become more of a problem than before they were sprayed.

• Cover bare dirt with mulch of dead leaves or grass clippings thick enough to shade the soil surface. This provides shelter for spiders, which are the number one predator on insects.

• Don't forget the birds. Birds can also be very helpful with controlling pests in your garden. Trees, shrubs with berries, birdhouses and water features all encourage birds to visit your yard.

Planting Flowers

Many beneficial insects are vagabonds that are always in search of prey. Flowers will attract beneficial insects to the garden, nourish them, and induce them to search your garden for pest insects. They provide these insectswith important resources, including:

- the sugar in nectar is used for energy in searching for prey, mating, and egg-laying

- the protein and fats in pollen are used to support egg development

- the flower is used as a place to locate mates

- small prey that live in flowers, such as thrips, which are a food source for immature predatory insects

Planting flowers will increase the likelihood that beneficial insects will colonize the garden and lay many eggs on the plants. After hatching, their young will crawl around the plants and feed on pest insects such as aphids, caterpillars, leaf beetle larva, thrips, spider mites, and whiteflies.

The plants that are most useful for supporting beneficial insects have small flowers with exposed nectar and pollen. Plants such as coriader (cilantro), dill (especially 'Bouquet' variety), fennel, and caraway are very attractive to beneficial insects. Alyssum, flowering buckwheat, black-eyed susans, dwarf sunflowers, and yarrow also attract these insects.

Five to ten percent of garden space should be dedicated to growing flowers for beneficial insects. The plants don't have to be massed to be effective, instead they can be tucked away in odd corners. Plant a succession of flowers to attract and support beneficial insects throughout the growing season. Avoid gaps without flowers as this will disrupt the colonization process. Most of these annuals will flower six to eight weeks after germination, so it is a good idea to plant a small batch of seeds every three or four weeks to ensure that flowers are available throughout the growing season. Removing spent flowers will extend the flowering period of individual plants. Avoid coriander (cilantro) varieties that are slow to bolt, as these take longer to flower. Buckwheat will flower as soon as three weeks after planting. Consider planting alyssum along the border of the vegetable garden in early spring.