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Beneficial Insects

Experts agree that only a very small percentage of the insects and spiders in our yards and gardens are actually pests, feeding on our desirable vegetation or infecting it with plant diseases. Indeed, many insects are helpful partners in our gardens, devouring aphids and other plant-eating pests. Pollinators like honeybees and butterflies are essential participants in the reproduction of many flowers, fruits and vegetables. Some small, stingless wasps or flies assist us by laying their parasitizing young on or inside doomed pests. Although beneficial insects won't keep our yards pest-free, their contributions should not be underestimated. Helpful links:

Helping beneficial insects feel at home

As a gardener, there are things you can do to help sustain natural populations of beneficial insects:

  • Provide their preferred and alternative foods Scatter a wide assortment of flowering plants throughout your garden and landscape or cluster them in a designated bed or border. Because different beneficial insects use pollen and nectar at different times, choose diverse plants with long, overlapping bloom periods. Pollinators aren't the only beneficials that rely on flowering plants. Nectar can help parasitoids (insects that develop in or on another insect pest) span periods when hosts are few. Nectar, pollen and plant juices can also help predators (insects such as ladybird beetle larvae, above, that consume other harmful insects) survive times when prey numbers are low.
  • Provide shelter Beneficial insects need protection from predators and human disturbances. These beneficial insects can find cover in perennial flower beds, hedgerows, cover crops and mulches.
  • Provide water Bird baths, shallow containers or temporary puddles, with sticks or rocks for perching, can help beneficial insects through dry periods. Change the water every two or three days to discourage mosquito breeding.
  • Protect them from insecticides Broad-spectrum insecticides kill beneficial insects right along with pests. To minimize impacts on beneficial insects, choose chemicals that are less toxic and more specific. Consider these environmentally "softer" alternatives: insecticidal soaps, horticultural oils, botanicals, Bacillus thuringiensis (Bt) and insecticidal products that act specifically as stomach poisons to foliage-feeding pests.

Description

Convergent lady beetles have black, dome-shaped bodies and up to 13 black spots on their orange to red hind wings. Their alligator-like larvae are orange and blue. Other common aphid-feeding lady beetles have different numbers or shapes of markings.

Life cycle

Convergent lady beetles lay their oblong yellow eggs on plant foliage, with the number of eggs laid dependent on the number of prey available. Development from egg to adult takes about three to six weeks. Adults migrate to mountain canyons or foothills to hibernate in late summer, flying back to the valleys in the very early spring.

Key benefits

Convergent lady beetles feed primarily on aphids but will also consume whiteflies, other soft-bodied insects and insect eggs. Both adults and larvae are aggressive predators; each day, adults can eat up to 50 aphids and larvae can devour the aphid equivalent of their body weight.

Damsel bugs are slender, grayish or tan insects that reach about 3/8-inch in length. They have elongated heads, long antennae and long legs. The first pair of legs is noticeably thicker than the other two pairs.

Life cycle

Damsel bugs overwinter as adults and lay their eggs in plant tissue. Nymphs look much like adults. About three or four generations occur each year.

Key benefits

Damsel bug adults and nymphs suck the body contents from aphids, small caterpillars, leafhoppers, plant bugs, thrips and mites. They also prey on insect eggs.

Adult green lacewings are slender, light green, ½- to ¾-inch long, with two pairs of large, clear, highly veined wings and golden eyes. They often fly in the evening or at night. Larvae, 1/8- to 4/5-inch long, resemble tiny, light-brown alligators.

Life cycle

Green lacewings overwinter as adults, generally in leaf litter. They lay their tiny oblong eggs at the ends of long, silken stalks. Larvae emerge in about 4-10 days and the larval stage lasts two to three weeks.

Key benefits

Adult green lacewings feed on aphid honeydew, nectar, pollen and plant fluids, although some species consume a few small insects. Their larvae-also called "aphid lions"-feed primarily on aphids, capturing them with their large pincers and sucking out their body fluids. During several stages of larval development, a single lacewing can consume as many as 750 aphids. Larvae also feed on leafhoppers, spider mites, thrips, mealybugs, psyllids, whiteflies, small caterpillars, immature plant bugs and other small insects.

Adult hover flies are generally brightly colored-with black-and-yellow abdominal bands-and closely resemble bees or wasps. They're typically ½- to ¾-inch long and have two wings. Their larvae, which can reach ½-inch in length, are sluglike, tapered toward the head and generally marked with a yellow longitudinal stripe on the back. Tell-tale black, oily smears of excrement on plant foliage reveal their presence.

Life cycle

Hover flies lay their whitish to gray oblong eggs singly on their sides near or within aphid colonies. They can have many generations per year.

Key benefits

Nonbiting, nonstinging adult hover flies feed on pollen, nectar and honeydew from aphids and scale insects. Their larvae consume aphids and other small, soft-bodied insects, including thrips and small caterpillars. A single larva can eat hundreds of aphids in a month. Hover fly larvae can detect low numbers of aphids and are particularly useful early in the season.

Description

Minute pirate bugs are 1/16-inch long, black-and-white insects with triangular heads and oval bodies. Their very active, pear-shaped nymphs are orange to amber and wingless.

Life cycle

Minute pirate bugs overwinter as adults and reproduce faster than any other common predatory insect. They can develop from egg to adult in as few as 15 days, producing several generations each summer.

Key benefits

Both adults and nymphs suck body fluids from spider mites, thrips, small aphids, white flies, caterpillars and insect eggs. They are often the first beneficial predators to appear in spring and can destroy 30 or more spider mites each day.

Description

Most parasitic wasps are tiny and black.

Life cycle

Parasitic wasps insert their eggs inside the bodies of aphids, loopers and other hosts. Larvae hatch inside their hosts, killing them and then cutting holes in their bodies to escape. Many generations occur each year.

Key benefits

Parasitic wasps attack aphids, scale, whiteflies, ants, leafminers, sawfly larvae and many types of caterpillars. They also parasitize the eggs of such insects as codling moths, tomato hornworms, cabbage loopers, imported cabbageworms and European corn borers.

Predacious ground beetles, ��- to 1¼-inch long, are typically black or dark metallic, with long legs and long antennae. Their larvae are slender, wormlike and fast-moving and use large pincers to capture their prey.

Life cycles

Predacious ground beetles overwinter as adults. Their larvae can take about a year to develop and some adults can live two to four years.

Key benefits

Both larvae and adults feed at night on a variety of insects, including armyworms, cutworms, grubs, small snails and slugs.

Description

Numbering about 3,000 U.S. species, spiders are a diverse group of predators. They're distinguished from insects by their two main body parts and eight legs.

Key benefits

In the Pacific Northwest, crab spiders are important predators that contribute to the overall natural control of many pest insects. They are general feeders that do not spin webs but instead lie in wait on foliage, grabbing their prey as it moves closer. Wolf spiders use their running speed to capture prey, which include both harmful and beneficial insects.

Description

Tachinid flies are large, dark and bristly, resembling bees, wasps or houseflies.

Life cycle

Some species lay their eggs on foliage, where a nearby host insect will feed on them. Others glue their eggs to the outside-or insert them inside-the host's body. The emerging larvae parasitize and kill the hosts. Tachinid flies complete one or a few generations each year.

Key benefits

Tachinid flies attack the larvae of butterflies and moths, beetles, sawflies and several other insect orders.

University of Idaho Extension

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Room 52
606 S Rayburn St.
Moscow, ID

Mailing Address:
University of Idaho Extension
875 Perimeter Drive MS 2338
Moscow, ID 83844-2338

Phone: 208-885-5883

Fax: 208-885-6654

Email: extension@uidaho.edu

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Barbara Petty