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Meet the insect do-gooders.

Meet the insect do-gooders

These garden warriors may not seem like something you'd want to invite into your garden. But despite their Martian-like looks or fierce names, these are the good guys of the bug world--parasitic and predatory insects that fly or crawl to overtake their prey (your plant pests) without much struggle. They're not harmful to plants, pets, or people.

The last few years have seen a surge in the availability of beneficial insects. The effectiveness of many kinds has been proven on farms, in shopping malls, in greenhouses, and in other areas where spraying is impractical or undesirable.

Home gardeners can find them through mail-order catalogs (see page 180 for some sources) and some in retail nurseries. However, there are few hard facts about their success in home gardens, where conditions are so variable. But entomologists from Colorado State University and several University of California campuses agree that, with the possible exception of praying mantises, parasitic nematodes, and adult ladybugs, each one described here is worth a try outdoors. If you're not too squeamish, many are good indoors, too.

Seven kinds of fighters for your garden

Here are some you can buy and what to expect from them. For detailed information on requirements for eliminating your own garden pests, write or call the sources given on page 180.

Green lacewing. Appropriately named the aphid lion, the larva of the lacewing may be the most effective insect against a broad spectrum of soft-bodied pests, including mealybugs, scale, and aphids. Shipped as small eggs in rice hulls, they hatch into hungry larvae within a few days. They feed for about three weeks, pupate, and emerge as adults, which lay eggs on the plant if sufficient pests remain. Adults feed on honeydew, not on pests, and they need honeydew to produce eggs. These lacewings occur naturally in most parts of the West.

Ladybug (properly called ladybird beetle).

Although ladybugs and their larvae have voracious appetites for aphids and other small insects, don't expect the adults to provide control once you release them from a mailing container into your garden.

The bugs you buy are collected in a dormant state during winter and are naturally programmed to disperse when temperatures rise. When you release them in your garden, few will stay longer than 24 hours. They're most effective if they migrate in naturally or if you release them into a confined space such as a greenhouse.

Mealybug destroyer. This member of the ladybug family, more likely to stick around, prefers to feed on mealybugs but also eats aphids and young scale if mealybugs aren't present. It days eggs in clusters of mealybugs; larvae look similar to mealybugs and have big appetites. It is most likely to stay if released in early evening when lower temperatures make it slower moving; it works best at 80| in high humidity. The destroyer is a good control in greenhouses and worth a try in the house or outside.

Parasitic nematodes. These attack various types of borers and soil-borne grubs. Even though some mail-order companies sell them, most experts describe their use as experimental and don't recommend you try them yet. The nematodes are very perishable, and best conditions for shipping and release are still being studied.

Parasitic wasps. Several species or groups of species parasitize immature stages of pests. One of the most useful is Encarsia formosa, which attacks the common whitefly larvae. It can be very successful in greenhouses and indoors where temperatures remain above 75|. If released when the whitefly population is still small, it may be effective outdoors as well.

Other parasitic wasps include Aphytis melinus, which attacks red scale; Metaphycus helvolus, which attacks black scale; and several species of Trichogramma which parasitize the eggs of pest worms such as corn earworms and cabbage worms. Each is worth a try in the garden when temperatures are above 70|.

Praying mantis. Fun to watch but not usually very effective, they can't keep up with fast-breeding pests and may eat as many bees and other desirable insects (including their own kin) as pests.

Predatory mites. Several species of almost invisible mites feed on plant-damaging spider mites. They're effective indoors, in greenhouses, and outdoors. Since they are perishable, release them as soon as you receive them. Predatory mites are most effective when a mixture of species is released, the humidity is high, and temperatures are above 70|. Control may take six to eight weeks. Predators die after controlling pests, so you'll have to release more if the plant-damaging mites return.

For the best results

Be patient. Beneficial insects are not a quick fix. Some take at least a few weeks to bring pests down to acceptable levels, and few will completely eliminate pests. Multiple releases are often necessary.

Release beneficial insects soon after you notice pests. But if pest populations are large, spray first with insecticidal soap (or apply Bacillus thuringiensis for caterpillars); these are least harmful to beneficial bugs. If you have already used a residual pesticide, such as Sevin or Diazinon, wait three to four weeks before releasing any insects.

Ants that farm the honeydew secreted by some types of scale, mealybugs, and aphids will actually battle some beneficial insects to protect the pests. Control ants with sticky barriers (available in many nurseries) smeared around base of trunks.

Attracting predators to your garden

Many suppliers of beneficial insects also sell a yeast-sugar combination--sometimes sold as artificial nectar--that attracts ladybugs and adult lacewings. Sprayed across the yard (plants and all) in a line perpendicular to prevailing winds, the spray causes windblown insects to mistake it for honeydew secreted by pests or for flower nectar. Once the beneficial insects are on the ground, they may be attracted to nearby pests or feed on the yeast-sugar long enough to lay eggs. You can make your own solution by combining equal parts brewer's yeast and sugar with just enough water so it dissolves completely. Apply with a clean, hand-pump sprayer.

Photo: Ladybug larva (above), about 1/3 inch long in actual size, attacks unlucky oleander aphid; adult (right) munches on another aphid. If you're fortunate, the adult and its offspring may stay in your garden. An adult ladybug can eat about 50 aphids a day, a larva up to 25

Photo: Mealybug destroyer, slightly smaller than a ladybug, enjoys catch. Three or four can clean up a medium-size house plant in a couple of days

Photo: Aphid lion (above), 1/3 inch long in actual size, eats an aphid. It also eats scale insects, thrips, mites, and leafhoppers. Aphid lion is the larva of the green lacewing (below)

Photo: Beneficial insects arrive by mail in containers or on tag. Clockwise from top left: ladybugs, larvae of Encarsia wasps, mealybug destroyers, and lacewing eggs

Photo: Fresh from the container, ladybugs take the first tentative crawl toward freedom (with a little help from the gardener). Will they stay in your garden? It's chancy
COPYRIGHT 1986 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1986 Gale, Cengage Learning. All rights reserved.

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Publication:Sunset
Date:Jul 1, 1986
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