Grow the right flowers to attract these Top 10 beneficial insects to your garden to minimize damage from aphids, caterpillars, flea beetles and other pests.
North America is home to nearly 2,000 species of braconid wasps.
ILLUSTRATION: KEITH WARD
Day and night, pesticide-free organic gardens are abuzz with activity, much of it a life-and-death struggle between predators and prey. We seldom see much of this natural pest control, in which tiny assassins, soldiers and lions — aka “beneficial insects” (the bugs that eat other bugs) — patrol their surroundings in pursuit of their next meal. Assassin bugs aren’t picky: They will stab, poison and devour a wide range of garden pests, including caterpillars, leafhoppers and bean beetles. Soldier and carabid beetles work the night shift, emerging after dark from beneath rocks, mulch and other daytime hiding places to feast upon soft-bodied insects and the eggs of Colorado potato beetles. Aphid lions (the larvae of the lacewing) have a hooked jaw that helps them dispatch huge numbers of aphids, caterpillars, mites and other pests.
These and many other beneficial insects (find profiles of our Top 10 later in this article and pictures of each in the Image Gallery) are well-equipped to see, smell and/or taste a potential meal. Sometimes they’re alerted by the plants themselves, as some emit a chemical alarm signal when pest insects begin feeding on them, and nearby beneficial insects are quick to respond. If your garden is teeming with beneficials, these bugs may often thwart budding pest infestations before you’ve even noticed the threat. It’s nature’s way of managing pests — no pesticides required.
Judging from reports from MOTHER EARTH NEWS readers across the continent, tapping the support of beneficial garden insects is one of our best tools for natural pest control. By providing a welcoming habitat — shelter, water and alternate food — you’ll encourage these insect helpers to maintain year-round residence in your garden. You can then kick back and enjoy the natural pest control provided by the diverse and amazingly complex balance among what we humans see as the “good bugs” and the “bad bugs.”
Habitats for beneficial bugs go by several names, such as “farmscape,” “eco-scape” and, in Europe, “beetle banks.” The concept of “farmscaping” to promote natural pest control isn’t new, but designing studies to confirm exactly what works best for a given crop in various regions is challenging. An increasing number of researchers has been exploring these complex interactions between insects and plants to find new ways gardeners and farmers can grow food without resorting to toxic pesticides. The information here will equip you to put this growing body of knowledge to work in your garden.
1. Plant a Nectary Smorgasbord of Flowers. When they can’t feed on insect pests in your garden, beneficial insects need other food to survive and reproduce. Having certain flowering plants in or near your garden supplies that food in the form of nectar and pollen. Beneficials use the sugar in nectar as fuel when searching for prey and reproducing, and the protein in pollen helps support the development of their eggs.
Which plants are easiest for them to tap? Researchers have identified the following groups whose flowers provide easily accessible nectar and pollen: 1) plants in the daisy family, such as aster, cosmos and yarrow; 2) plants in the carrot family, such as cilantro, dill, fennel, parsley and wild carrot; 3) alyssum and other members of the mustard family; 4) mints; and 5) buckwheats.
Plants in these families are especially good because their clusters of very small flowers make accessing their nectar and pollen easier for many insects. For a longer list of flowers that support beneficials, check out Organic Pest Control: The Best Plants to Attract Beneficial Insects and Bees, and if you’ve noticed plants in your garden that are bustling with insects while flowering, tell us about them in the comments section of that page.
Beneficial garden insects can be broadly categorized as generalists — those that eat most anything they can catch — and specialists — those that feed on just one or a small array of prey. The plants mentioned above can be used by both types, says Mary Gardiner, assistant professor of entomology at Ohio State University.
“Also be sure to consider bloom time,” Gardiner says. “You want to provide a diversity of flowers from early to late in the season so that food is always available for the beneficials.”
In addition, be sure to include some plants with extrafloral nectaries, which are nectar-producing glands apart from the plant’s flowers. Such plants are an important supplemental food source for lady beetles and other beneficial insects, especially during periods of drought or other extreme weather. Plants with extrafloral nectaries include sunflower, morning glory, peony, elderberry, vetch, willow, plum and peach.
Until your season-long flower supplies become well-established, you can supplement beneficials’ diets with a simple solution of sugar water. Several studies conducted by Utah State University found a sugar solution effective for attracting parasitic wasps. The researchers used a mix of about three-quarters of a cup of sugar per 1 quart of water, and they applied it in a fine mist with a handheld sprayer onto the crop’s foliage. (The researchers used the solution on alfalfa.) Be sure to use fresh solution, Gardiner advises.
For more information about plants that attract beneficials, see our 19 Plants Beneficial Insects Love chart.
2. A Home of Their Own. Rather than just interplanting a few of these flowering plants within your vegetable garden, try to give them a wider berth: their own permanent space near your garden crops. Doing so will help create an undisturbed habitat where insect predators and parasites can feed, reproduce and overwinter. Many beneficials, including ground beetles and soldier beetles, spend at least part of their life cycle underground, so having patches of soil that won’t be churned up by digging or tilling is helpful.
“By taking an annual cropping system and adding borders or strips of diverse perennial vegetation, we mimic natural systems,” says Don Weber, a research entomologist with the Agricultural Research Service who is based in Beltsville, Md. “From there, predators can move quickly into nearby annual crops to help suppress pests.”
3. Go Native. Beneficial and pest species vary regionally, so be sure to incorporate some native plants into your beneficial habitat. Native plants provide not only nectar and pollen but also alternate insect prey. “Take milkweed, for instance,” Gardiner says. “It hosts aphids, which draw in lady beetles. The native aphids only feed on the milkweed, but the lady beetles can go on to feed on garden pests.” Native plants have other benefits, too: They increase biodiversity and provide food for birds and native bees.
In 2004 and 2005, researchers at Michigan State University tested 46 native plants and identified a group that provided flowers throughout the growing season and attracted a diversity of beneficial insects (you can see the results at Michigan State University Native Plants and Ecosystem Services). What set the winners apart? All had very showy floral displays.
“That could be due to either having large individual blooms, like the cup plant, or a large number of smaller blooms that together appear large, like the milkweeds,” says Doug Landis, the Michigan State University entomologist who led the study. Landis advises gardeners in other regions to select natives that are known to be insect-pollinated, that grow vigorously in the specific conditions and that have large floral displays.
4. Hedge Your Bets. Include shrubs and perennial grasses in or near your garden, too, if possible. California researchers have taken a long, hard look at hedgerows to find out how they may be able to increase beneficial insect activity on farms. Hedgerows — diverse plantings of native flowering perennials, grasses, shrubs and trees — were previously used as windbreaks, boundary markers and sources of wood, but have become less common in recent decades.
The studies have shown that a hedgerow can provide an ideal habitat for many beneficial bugs, such as predatory bugs (assassin bugs and minute pirate bugs), syrphid flies, lady beetles, and parasitic wasps and flies. From the shelter of a hedgerow, these “good bugs” can quickly move to nearby garden crops to feed on aphids, caterpillars, leafhoppers and squash bugs.
“Once these hedgerow plants are established, they can bloom for a long period and produce a large quantity of flowers with high-quality nectar,” says Rachael Long, farm adviser with the University of California Cooperative Extension Service. “Hedgerows provide shelter from wind and cold, too, as well as alternate prey species, which is especially important at the end of the growing season when beneficials need a place to overwinter. It encourages them to stay in the area.”
In a home garden setting, even a small mixed border of shrubs, grasses and perennial flowers should achieve similar results. Select plants with different bloom times, advises Long. The closer the planting is to garden crops, the better, although beneficials will travel as far as several thousand feet if necessary.
One note of caution: Letting the margins of your property go “wild” with weeds is not necessarily the kind of diversity you want to encourage. “We found that weedy, semi-managed areas actually were a resource for insect pests, while managed hedgerows with native plants had fewer pests and more beneficials that moved to nearby crops,” Long says. (For more information on the findings, see Establishing Hedgerows on Farms in California.)
5. Cover More Ground. Cover your soil with an organic mulch or cover crop. Bare ground exposes beetles, spiders and other beneficial garden insects to climate extremes (temperature, wind, humidity) that can threaten their survival. “Use any locally available organic mulch,” Gardiner says. “As long as it helps retain moisture, is well-aerated, and is not infected with fungal pathogens, it will protect the beneficials from the sun and also provide food for some predators as it decays.”
Cover crops such as buckwheat, cowpea, sweet clover, fava bean, vetch, red clover, white clover and mustards can also provide food and shelter for beneficials. “The key is to make sure that both the cover crop and food crops overlap for at least some of the time, so beneficials can move directly from the cover crop to the crop pests,” says Robert Bugg, a University of California, Davis entomologist who has been studying the relationship between plants and beneficials for several decades. (A comprehensive cover crop database is available on the UC Sustainable Agriculture Research and Education Program website. Entries include information about a crop’s attractiveness to beneficial insects and other selection criteria.) At the end of the season, ignore the conventional advice to remove all spent vegetation. If you know you have a pest that will overwinter in the debris, go ahead and remove it or till it under. But if not, leaving the debris is better because beneficials will seek shelter in it. Bunch grasses and clumping perennials such as comfrey provide especially good winter shelter for a number of beneficial insects.
6. Water Works. Provide shallow, gravel-filled dishes of water in your garden if you don’t have other water sources such as ponds or wetlands nearby to support beneficial insects (including native bees). Be careful to change the water frequently to avoid creating a habitat for mosquitoes. Better yet, try growing the cup plant (Silphium perfoliatum), which holds water in its leaves.
7. Use Organic Insecticides Selectively. Insecticides are designed to kill insects, and even natural, plant-based pesticides such as pyrethrum can kill beneficials. Use only pesticides approved for use by organic growers, use them as a last resort, and use them selectively. Besides, experts say having a few insect pests in your garden isn’t so bad anyway — they help keep the good guys hangin’ around, hungry for more.
1. Braconid Wasps (Hymenoptera): North America is home to nearly 2,000 species of these non-stinging wasps. Adults are less than half an inch long, with narrow abdomens and long antennae. Adults lay eggs inside or on host insects; the maggot-like larvae that emerge consume the prey. Diet: Caterpillars (including tomato hornworms), flies, beetle larvae, leaf miners, true bugs and aphids. Adults consume nectar and pollen.
2. Ground Beetles (Coleoptera): Most of the 2,500 species are one-eighth to 1 1/2 inches long, dark, shiny and hard-shelled. Diet: Asparagus beetles, caterpillars, Colorado potato beetles, corn earworms, cutworms, slugs, squash vine borers and tobacco budworms. Some are also important consumers of weed seeds.
3. Hover or Syrphid Flies (Diptera): Larvae are small, tapered maggots that crawl over foliage. Black-and-yellow-striped adults resemble yellow jackets but are harmless to humans. The adults hover like hummingbirds as they feed from flowers. Diet: Larvae eat mealybugs, small caterpillars, and are especially helpful in controlling early season aphids. The adults feed on nectar and pollen.
4. Lacewings (Neuroptera): Larvae, sometimes called “aphid lions,” measure to half an inch long and are light brown with hooked jaws. Adults are light green or brown and one-half to 1 inch long with transparent wings. Diet: Larvae prey upon aphids, small caterpillars and caterpillar eggs, other larvae, mealybugs, whiteflies and more. Adults eat honeydew, nectar and pollen, and some eat other insects.
5. Lady Beetles (Coleoptera): All of the nearly 200 beneficial North American species are one-quarter-inch long. Larvae, which can resemble tiny alligators, are usually dark and flecked with red or yellow. Adults are rounded and often have orange or red bodies with black spots. Diet: Larvae and adults both dine on aphids, small caterpillars, small beetles and insect eggs. Specialist species feed on scale insects, mealybugs, mites and even powdery mildew. Adults also eat honeydew, nectar and pollen.
6. Predatory Bugs (Hemiptera): This group includes big-eyed (see Image Gallery), minute pirate, assassin, damsel and even certain predatory stink bugs. All use their mouth, or “beak,” to pierce and consume prey. Adults range in size from the minute pirate bug (one-sixteenth-inch long) to the wheel bug (an assassin bug that’s 1 1/2 inches long). Diet: Nymphs or larvae and adults feed on aphids, caterpillars, scale insects, spider mites and insect eggs. Many also prey upon beetles.
7. Soldier Beetles (Coleoptera): These elongated, half-inch-long beetles have soft wing covers. Larvae are brownish and hairy. Adults usually have yellow or red and black markings and resemble fireflies. Diet: Larvae feed on the eggs and larvae of beetles, grasshoppers, moths and other insects. Adults feed on aphids and other soft-bodied insects, as well as on nectar and pollen.
8. Spiders (Araneae): All of the more than 3,000 North American species — including the crab spider, jumping spider, wolf spider and orb-web spider — are predatory. Diet: Depends on species, but can include aphids, beetles, cutworms, fire ants, lacebugs, spider mites, squash bugs and tobacco budworms.
9. Tachinid Flies (Diptera): There are more than 1,300 North American species of parasitic flies. Most resemble houseflies but with short, bristly hairs on the abdomen. All develop as internal parasites of other insects, including many garden pests. Usually, the adult female attaches its egg to the host insect, which is then consumed by the larva, but there are several other patterns: eggs laid on host, eggs laid into host, eggs laid on foliage to be eaten by host, live larvae laid on or near host, and live larvae laid into host. Diet: Larvae feed internally on caterpillars, beetles, bugs, earwigs and grasshoppers. Adults feed on nectar, pollen and honeydew.
10. Trichogramma Mini-Wasps (Hymenoptera): These extremely small wasps lay their eggs inside the host’s eggs, where the young trichogramma develop as internal parasites. Parasitized eggs turn black. Because the trichogramma’s life cycle is very short — just seven to 10 days from egg to adult — their populations can grow rapidly. Diet: Pest eggs, especially those of cabbageworms, codling moths, corn earworms, diamondback moths, and other moths and butterflies.
Keep these and other beneficials coming back by planting our 19 recommended plants for attracting beneficial insects in and around your garden.
When pest insects attack crops, many plants release chemicals that signal to beneficial insects that lunch is nearby. One of the more common HIPPOs — Herbivore-Induced Plant Protection Odors — is methyl salicylate, aka oil of wintergreen. Numerous studies have confirmed that oil of wintergreen attracts a variety of beneficial insects, including ladybugs, lacewings, minute pirate bugs and aphid-eating hover flies. Controlled-release dispensers of this fragrant oil are marketed as PredaLures and cost about $5 each at Grow Organic. Or, take a DIY approach by soaking cotton balls in the oil, then placing them in the garden inside empty cottage cheese containers with perforated lids. — Cheryl Long
Garden Insects of North America by Whitney Cranshaw
Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control by Mary Louise Flint and Steve H. Dreistadt
Managing Cover Crops Profitably from Sustainable Agriculture Research & Development
Veteran garden writer Vicki Mattern is one of America’s leading experts in organic gardening. She currently homesteads on 3 acres in northwestern Montana.