It happens every spring. First, a few aphids appear on the coal crops. A week later, the aphids have doubled. You start to get concerned. After another week, the number have grown again. Should I panic? Reach for the soap spray? Will my helpers come to my aid again this year? And then, one morning, there they are: a ladybug is wandering among the aphids, dining contentedly. In a few days, there’s hardly an aphid to be found. I’m always amazed that the ladybugs come in such numbers, and at the right time. And they always do the job.
Our garden consist of numerous vegetable beds surrounded by a diverse border of annual and perennial flowers, herbs, and fruit trees. Next to the garden are wild areas where some of the less troublesome weeds grow to maturity. Among the vegetable beds are areas of clover and buckwheat. In these places, a militia of beneficial insects do well, ready to emerge to eat or paralyz other insects that may be harmful to our plants. On a warm summer day, I can see a light haze of tiny parasitic wasps visiting the fennel flowers in search of nectar. The nectar will sustain them while they are on the lookout for aphids or caterpillars in which they deposit their eggs. It’s a relief to have such for formidable allies.
To create a welcoming habitat for the insect helpers, first you need to know something about them. A good way to start is to grab a hand lens and a picture book of insects and take a rough census of your resident population. If you’ve avoided using pesticides and have a variety of plants growing, you will find many allies already present. The ones you’re most likely to see include ladybugs, lacewings, hover flies, praying mantises, and a few tiny beneficial wasps. These can be divided into two groups: those that eat their prey directly (predators) and those that deposit their eggs on or into their host (parasitoids).
The two kinds of beetle that are most helpful are ladybugs and ground beetles, both predators.
Ladybugs pray on aphids and other soft-bodied insects. The adults will eat as many as 50 aphids per day. If you have enough aphids, and the beetles stick around long enough to lay eggs, each hatched larva will eat some 400 aphids before entering its pupal stage. There are many species of ladybugs that attack many different prey. The adults are independent flight creatures. If you buy some at the garden center and release them into your garden, be prepared to watch most of them fly away to your neighbor’s yard. Those that stay, though, will be a big help.
When the fairylike green lacewing flutters silently by in search of pollen or nectar, I find it hard to imagine it in its fiercely predatory larval stage, during which it devours aphids, caterpillars, mealybugs, leafhoppers, insect eggs, and whiteflies. If you keep a supply of flowering plants, adult lacewings may take up residence. If you decide to introduce beneficial insects to your garden, lacewings are the most effective predators you can buy.
With their striped abdomens, hover flies look like small bees, but they move through the air more like flies, zipping from plant to plant and hovering briefly before landing. The hover fly is one of many predatory flies and the most conspicuously beneficial insect in the garden. I can find them just about any time anywhere in the garden. They visit a variety of flowers in search of pollen and nectar and lay their eggs near aphids or other soft-bodied insects. The eggs hatch into hungry larvae that eat up to 60 aphids per day.
Parasitic wasps are very helpful creatures, ranging in size from small to minuscule. They will defend your garden against caterpillars like corn earworms as well as tomato fruit worms, cabbage worms, and tent caterpillars. The smallest and perhaps most popular parasitic wasp is trichogramma, a dust-size creature that lays up to 300 eggs in moth or butterfly eggs. You can buy them through the mail if you’re expecting a population of caterpillars. They don’t live very long, so timing in their release to coincide with the presence of caterpillar eggs is pretty important.
The parasitic wasps either kill the hosts or disrupt their activities. If you were scouting with a hand lens and noticed some mummified aphids with neat circular holes in them, you’ll know a parasitic wasp was there. A young wasp developed inside the aphid and ate its way out.
If you build it, they will come
We’re living in a bug-eat-bug world. I transformed my garden into an insectary, a habitat where my beneficial insect friends will feel at home. I provide them with food, water, and shelter. I keep the soil covered with organic matter. And I avoid putting any harmful chemicals in their habitat.
The menu for beneficial insects changes constantly as pest populations shrink and swell and different flowers come into bloom. Many of the predators and most of the parasites will use pollen and nectar for food. I try to sustain them throughout the year by growing a variety of flowers that bloom at different times. Since many of the beneficial insects are tiny and have short mouthparts, I offer them tiny flowers with short nectaries. Many plants in carrotsand aster families offer just that.
I water my garden occasionally with an overhead sprinkler so insects always have puddles and wet leaves to drink from. If I were using drip irrigation, I’d offer them water in a saucer filled with pebbles so that they don’t drown.
Just like the rest of us, beneficial insects need protection from heat and rain. They need to hide from birds and insects that would love to make a meal out of them. Again, a variety of leafy plants offer protection. Beetles hide in the low-growing ground covers and in mulch or leaf litter. Flying insects hide in shrubs on the undersides of leaves and even among the petals of marigolds.
Beneficial insects also need a reason to stay when they finish cleaning up the crops or at the end of the season when you’ve cleaned up the garden. Consider trying to recreate a corner of the yard or edge of your garden with a thick, wild diversity of hedgerow by using a variety of early flowering shrubs, perennials, and grasses to provide year-round shelter and a place for alternative prey to do well. Keep the beneficial insect reservoir close to your garden. If insects get too comfortable in the hedgerow, they might not be inclined to travel very far for a meal. As long as there’s a place for pests, the beneficial insects may stay and eat in your weedy refuge rather then head for the neighbor’s yard.
Insect allies hate dust. Keeping the soil covered at all times, either with mulch or with growing plants, conserves moisture, moderates temperature, and eliminates dust. It also provides habitat for ground and rove beetles. Try not to eliminate every weed. Leave some for the insects.
Creating a habitat for wild insects is a very imprecise endeavor. With experimentation and observation, you may hit on the right combination of insectary plants that entices the right combination of insects to your garden. Your success will probably vary from year to year as the climate and vegetation change and new pests arrive. You should expect the development of a habitat where pests and beneficials exist in a rough balance for several years rather than a season or two. Despite the presence of so many beneficial insects in our garden, I still find myself from time to time having to handpick squash bugs or rub scales from branches of the fruit trees. That’s gardening!
Creating a habitat can be a colorful affair. Start luring beneficial insects quickly with annuals like alyssum, cosmos, zinnias, sunflowers, and marigolds. At the same time, set out perennial flowers and herbs, including yarrow, lavender, mint, fennel, angelica, and tansy. Beneficials are also fond of dill, parsley, and cilantro flowers. When you’ve finished harvesting these herbs, leave the plants in the ground to flower. I like to let a small patch of carrots run to flower. Their blossoms are sweetly fragrant. Beneficial insects love them.
A few tips for attracting beneficial insects in beautiful ways
—A mix of annual and perennial flowers provide alternative food sources for beneficial insects when prey insects are scarce.
—In addition to hover flies, the yellow button flowers of tansies attract ladybugs, lacewings, and parasitic wasps.
—Statice is a good annual source of nectar; come fall, bring cut stems indoors for everlasting winter color.
—The tiny flowers of umbelliferous plants like fennel are especially attractive to lacewings but also to hover flies, parasitic wasps, and ladybugs. Plus, they are a great place for the swallowtail butterfly to feed.
—A big planting of sweet alyssum is a season-long nectar factory and a perfect haven for lots of beneficial insects.
—The flat blossoms of zinnias and Mexican sunflowers make good insect landing pads, and the shallow nectar-bearing flowers are easy for beneficial insects to drink from.
—Don’t be in a hurry to pull parsley at season’s end. Allow it to stay over the winter. The next year, it will produce food for good insects.
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