|Beneficial Insects: Your Garden’s Most Powerful Allies
Our insect allies far outnumber the insect pests in our yards and gardens. Bees, flies, and many moths help gardeners by pollinating flowers; predatory insects eat pest insects; parasitic insects lay their eggs inside pests, and the larvae that hatch then weaken or kill the pests; dung beetles, flies, and others break down decaying material, which helps build good soil.
Bees and Wasps
Honeybees are called the “spark plugs” of agriculture because of their importance in pollinating crops, but other wild bees and wasps are also important pollinators and natural pest-control agents.
Bees: All bees gather and feed on nectar and pollen, which distinguishes them from wasps and hornets. As they forage for food, bees transfer stray grains of pollen from flower to flower and pollinate the blooms. There are some 20,000 species of bees worldwide. Of the nearly 5,000 in North America, several hundred are vital as pollinators of cultivated crops. Many others are crucial to wild plants.
Pesticide use, loss of habitat, and pest problems such as mites have vastly reduced wild and domestic bee populations. Most recently, a phenomenon called Colony Collapse Disorder is decimating populations of honeybees in the United States. It’s not known for sure what is causing this problem, in which worker bees suddenly die out, leaving behind the queen bee, the nurse bees, and the unborn brood (which in turn die without the support of the worker bees). Possibilities include diseases or parasites, or damaging effects of chemical pesticides on bees’ nervous systems or immune systems.
The good news is that native bees ranging from bumblebees to tiny “sweat bees” are still hard at work pollinating crops and gardens. The best way to encourage native bees is to tend a flower garden with as long a bloom season as possible. Leave some bare ground available for the bees to tunnel in to make nests, and provide a shallow water source where they can drink.
Parasitic wasps: Most species belong to one of three main families: chalcids, braconids, and ichneumonids. They range from pencil-point-size Trichogramma wasps to huge black ichneumonid wasps. Parasitic wasps inject their eggs inside host insects; the larvae grow by absorbing nourishment through their skins.
Yellow jackets: Most people fear yellow jackets and hornets, but these insects are excellent pest predators. They dive into foliage and carry off flies, caterpillars, and other larvae to feed to their brood. So don’t destroy the gray paper nests of these insects unless they are in a place frequented by people or pets, or if a family member is allergic to insect stings.
While some beetles, such as Japanese beetles and Colorado potato beetles, can be serious home garden pests, others are some of the best pest-fighters around.
Lady beetles: This family of small to medium, shiny, hard, hemispherical beetles includes more than 3,000 species that feed on small, soft pests such as aphids, mealybugs, and spider mites. (Not all species are beneficial—for example, Mexican bean beetles also are lady beetles.) Both adults and larvae eat pests. Most larvae have tapering bodies with several short, branching spines on each segment; they resemble miniature alligators. Convergent lady beetles (Hippodamia convergens) are collected from their mass overwintering sites and sold to gardeners, but they usually fly away after release unless confined in a greenhouse.
Ground beetles: These swift-footed, medium to large, blue-black beetles hide under stones or boards during the day. By night they prey on cabbage root maggots, cutworms, snail and slug eggs, and other pests; some climb trees to capture armyworms or tent caterpillars. Large ground beetle populations build up in orchards with undisturbed groundcovers and in gardens under stone pathways or in semipermanent mulched beds.
Rove beetles: These small to medium, elongated insects with short, stubby top wings look like earwigs without pincers. Many species are decomposers of manure and plant material; others are important predators of pests such as root maggots that spend part of their life cycle in the soil.
Other beetles: Other beneficial beetles include hister beetles, tiger beetles, and fireflies (really beetles). Both larvae and adults of these beetles eat insect larvae, slugs, and snails.
We usually call flies pests, but there are beneficial flies that are pollinators or insect predators or parasites.
Tachinid flies: These large, bristly, dark gray flies place their eggs or larvae on cutworms, caterpillars, corn borers, stinkbugs, and other pests. Tachinid flies are important natural suppressors of tent caterpillar or armyworm outbreaks.
Syrphid flies: These black-and-yellow or black-and-white striped flies (also called flower or hover flies) are often mistaken for bees or yellow jackets. They lay their eggs in aphid colonies; the larvae feed on the aphids. Don’t mistake the larvae—unattractive gray or transluscent sluglike maggots—for small slugs.
Aphid midges: Aphid midge larvae are tiny orange maggots that are voracious aphid predators. The aphid midge is available from commercial insectaries and can be very effective if released in a home greenhouse.
Dragonflies: Often called “darning needles,” dragonflies and their smaller cousins, damselflies, scoop up mosquitoes, gnats, and midges, cramming their mouths with prey as they dart in zig-zag patterns around marshes and ponds.
Lacewings: The brown or green, alligator-like larvae of several species of native lacewings prey upon a variety of small insects, including aphids, scale insects, small caterpillars, and thrips. Adult lacewings are delicate, ½- to 1-inch 82green or brown insects with large, transparent wings marked with a characteristic fine network of veins. They lay pale green oval eggs, each at the tip of a long, fine stalk, along the midrib of lettuce leaves or other garden plants.
True bugs: True bug is the scientifically correct common name for a group of insects. This group does include several pest species, but there are also many predatory bugs that attack soft-bodied insects such as aphids, beetle larvae, small caterpillars, pear psylla, and thrips. Assassin bugs, ambush bugs, damsel bugs, minute pirate bugs, and spined solider bugs are valuable wild predators in farm systems.
Spiders and mites: Although mites and spiders are arachnids, not insects, they are often grouped with insects because all belong to the larger classification of arthropods. Predatory mites are extremely small. The native species found in trees, shrubs, and surface litter are invaluable predators. Phytoseiid mites control many kinds of plant-feeding mites, such as spider mites, rust mites, and cyclamen mites. Some also prey on thrips and other small pests. Many types of soil-dwelling mites eat nematodes, insect eggs, fungus gnat larvae, or decaying organic matter.
It’s unfortunate that so many people are scared of spiders, because they are some of the best pest predators around. We are most familiar with spiders that spin webs, but there are many other kinds. Some spin thick silk funnels; some hide in burrows and snatch insects that wander too close, while others leap on their prey using a silk thread as a dragline.
The best way to protect beneficial insects is to avoid using toxic sprays or dusts in the garden. Even organically acceptable sprays such as insecticidal soap and neem can kill beneficial species, so use them only when absolutely necessary to preserve a crop and then only on the plants being attacked. Be careful when you hand pick or spray pest insects, or you may end up killing beneficial insects by mistake. While many beneficials are too small to be seen with the unaided eye, it’s easy to learn to identify the larger common beneficials such as lacewings, tachinid flies, and lady beetles.
You can make your yard and garden a haven for beneficials by taking simple steps to provide them with food, water, and shelter.
Food sources: A flower bed or border of companion plants rich in pollen and nectar, such as catnip, dill, and yarrow, is a food source for the adult stages of many beneficials, including native bees, lacewings, and parasitic wasps.
Water: Many types of beneficial insects are too small to be able to drink water safely from a stream, water garden, or even a regular birdbath. To provide a safe water supply for these delicate insects, fill a shallow birdbath or large bowl with stones. Then add just enough water to create shallow stretches of water with plenty of exposed landing sites where the insects can alight and drink without drowning. You’ll need to check this bug bath daily, as the water may evaporate quickly on sunny days.
Shelter: Leave some weeds here and there among your vegetable plants to provide alternate food sources and shelter for beneficial species. Plant a hedge or build a windbreak fence to reduce dust, because beneficial insects dehydrate easily in dusty conditions. And set up some permanent 83pathways and mulched areas around your yard and garden. These protected areas offer safe places for beneficials to hide during the daytime (for species that are active at night), during bad weather, or when you’re actively cultivating the soil.
Attracting beneficial insects. Making your garden a haven for beneficial insects is easy and fun. It’s also one of the cheapest and most environmentally sound ways to help prevent insect pests from getting the upper hand on your food crops and ornamentals.
To learn more about encouraging beneficial insects in your yard, visit the Web sites of organizations such as the Xerces Society.
Buying Beneficial Insects
Many garden supply and specialty companies offer beneficial insects for sale to farmers, nursery owners, and gardeners. You can buy everything from aphid midges to lady beetles and lacewings to predatory mites.
Buying and releasing beneficial insects on a large scale, such as a commercial farm field, or in a confined place, such as a greenhouse, can be a very effective pest-control tactic. However, in a typical home garden it’s rarely worthwhile. Chances are that most of the insects you release will disperse well beyond the boundaries of your yard. While that may be helpful for your neighborhood in general, it won’t produce any noticeable improvement in the specific pest problem that you hoped the good bugs would control in your garden. Overall, it’s more effective to invest money in plants that attract beneficial insects to your yard than it is to buy and release beneficial insects.
If you decide to experiment with ordering beneficial insects, make sure you identify the target pest, because most predators or parasites only attack a particular species or group of pests. Find out as much as you can by reading or talking to suppliers before buying beneficials.
Get a good look at the beneficials before releasing them so that you’ll be able to recognize them in the garden. You don’t want to mistakenly kill them later on, thinking them to be pests. A magnifying glass is useful for seeing tiny parasitic wasps and predatory mites. Release some of the insects directly on or near the infested plants; distribute the remainder as evenly as possible throughout the rest of the surrounding area.
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