Attract Beneficial Insects to Your Gardencomments (0) April 6th, 2009
It happens every spring. First a few aphids appear on the cole crops. I barely notice. A week later the aphids have doubled. I start to get concerned. After another week the number has 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, lady beetles wandering among the aphids, dining contentedly. In a few days there’s hardly an aphid to be found. I’m always amazed that the lady beetles come in such numbers, and at the right time. And they always do the job.
Our garden consists 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. And among the vegetable beds are plots of alfalfa, clover, and buckwheat. In these places dwell a militia of beneficial insects, ready to emerge to eat or parasitize 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 look for aphids or caterpillars in which to deposit their eggs. It’s a relief to have such formidable allies. I haven’t needed even an organic pesticide in 15 years.
|A folding 10-power hand lens will help you tell the good bugs from the bad, and keep tabs on who's winning.|
To create a welcoming habitat for your 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 may find many allies already present. The ones you’re most likely to see include lady beetles, ground beetles, lacewings, hover flies, a couple of true bugs, and a few tiny 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 lady beetles (a.k.a. ladybugs) and ground beetles, both predators.
Lady beetles prey 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 lady beetle that attack many different prey. The adults are independent, flighty 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.
|There are many different lady beetles (left), all beneficial as both larvae and adults. They overwinter as adults, congregating on leaf undersides in mild climates. In cold winter areas, you may find them camping out in your house. Lady beetle larvae (right) eat eight times as many aphids as adult lady beetles do.|
|During the day, ground beetles hide in plant debris. At night, they emerge to hunt for insect eggs and larvae.|
Ground beetles don’t fly much, preferring to run away when disturbed. You probably won’t see them unless you uncover their hiding places. If I see them at all, it’s when I’m picking up old piles of weeds. They’re relatively large (about 3⁄4 inch), and dark, with long, jointed legs. They’re nocturnal hunters, rooting among leaf litter for insect eggs and larvae
Our garden is also home to hoards of soldier beetles, which show up for the late spring aphid feast. And I sometimes encounter mite-and-snail-destroying rove beetles that inhabit piles of decaying organic matter.
When the fairylike green lacewing flutters silently by in search of pollen or nectar, I find it hard to imagine it in its fiercely predacious larval stage (photos #5 and #6, p. 13), during which it devours aphids, caterpillars, mealybugs, leafhoppers, insect eggs, and whiteflies. It even eats other lacewings. Up close, the larva looks like a tiny (1⁄2 inch) alligator. If you keep a supply of flowering plants, adult lacewings may take up residence. If you decide to introduce beneficials to your garden, lacewings are the most effective predators you can buy.
|What a difference a couple of weeks makes. From gray alligator-like larvae (left), gowwamer-winged green lacewings develoop (above). If you're going to buy predators, lacewings are a good bet because they eat a wide range of harmful insects.|
|It looks like a honey bee, but it's not. Hover flies (also called syrphid flies) are common predators and easy to spot.|
With their striped abdomens, hover flies look like small bees, but they move through the air more like flies, zipping from plant to plant, hovering briefly before landing. The hover, or syrphid, fly is one of many predatory flies and the most conspicuous beneficial in our garden. I can find them just about anytime anywhere in the garden. They visit a variety of flowers in search of pollen and nectar, and they lay their eggs near aphids or other soft-bodied insects. The eggs hatch into hungry larvae that eat up to 60 aphids per day.
There are bugs and then there are true bugs. True bugs, like the minute pirate bug and the big-eyed bug, belong to the insect order Hemiptera. Many are plant feeders but many are predacious, with tubular mouthparts they insert like a straw to suck the juices out of their prey.
The minute pirate bug is a tiny (1⁄12 inch) predator with a wide-ranging appetite; it eats aphids, thrips, mites, whiteflies, and insect eggs. It lays its eggs on the leaf surface near its prey; nymphs hatch and begin feeding. The cycle from egg to adult takes only three weeks.
The other important true bug is the big-eyed bug. It’s a little bigger than the minute pirate bug and has a similar diet. It also eats nectar and seeds, so it may stay even if it can’t find an insect to eat.
You might come across some other common predatory true bugs, including assassin bugs, damsel bugs, thread-legged bugs, and a couple of species of stinkbug.
|Trichogramma wasps look like tiny black flies. Here, they are working a mass of gypsy moth eggs.|
These very helpful creatures, ranging in size from small to minuscule, will defend your garden against caterpillars like corn earworm, tomato fruitworm, cabbageworm, and tent caterpillars. The smallest and perhaps most popular parasitic wasp is the 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 an infestation of caterpillars. They don’t live very long so timing their release to coincide with the presence of pest eggs is pretty important.
Braconid, chalcid, and ichneumid wasps are much larger than trichogramma, and parasitize caterpillars directly, laying eggs in or on the caterpillar. The hatching eggs eventually either kill the host or disrupt its activities. Braconids parasitize aphids as well. If you’re scouting with a hand lens and notice some mummified aphids with neat circular holes in them, you’ll know a braconid was there. A young wasp developed inside the aphid and ate its way out.
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