Gardening Articles :: Edibles :: Vegetables :: National Gardening Association

Gardening Articles: Edibles :: Vegetables

The Do-Good Bugs

by Whitney Cranshaw

Spined soldier bug feeds on a Mexican bean beetle larva

Insects are the most successful living organisms on the Earth. That's just one reason it makes good sense to balance one against the other, rather than trying to kill pests with poisons. It is also true that in nature there are no good or bad bugs. All are trying to make a living in the way nature programmed them. But from a gardener's perspective, some insects help and some don't. It's smart to learn about and exploit insect behaviors. In this article you'll learn how to wisely purchase and use beneficial insects.

Using insects to control other insects has a long history. Ancient Chinese records describe the construction of bamboo runways to help predatory ants move through citrus groves, and for hundreds of years Yemeni nomads brought ant colonies from the mountains to control palm pests in oases. Modern biological control began in 1888 when a small lady beetle was brought from Australia to California. This effort, organized by state and federal agencies, saved the citrus industry from the cottony cushion scale and was successfully repeated dozens of times worldwide.

There are two kinds of beneficial insects: predators and parasites. Predators eat or otherwise destroy one or more other insect pests directly. Parasites complete their life cycles in a specific host, destroying it in the process. Today there are nearly 100 mail-order companies in the United States (and more in Canada and Mexico) either producing or selling several dozen species of predatory and parasitic insects. Most of these are used in agriculture, of course, especially in greenhouses. But a few are well-known garden beneficials.

Releasing large quantities of a beneficial insect into your garden can work in several ways. Sometimes it's like a biological insecticide: The bugs you buy go straight to your pests, clean them up and then disperse or die off. Sometimes the beneficials have limited effectiveness on target pests, but then go on to establish a local population of beneficial offspring that live on from year to year, helping to reduce the background level of pests. And sometimes the good bugs consume just a few of your pests before flying away.

When we say that one of the insects described below provides control, we mean that a release can make a significant dent in the population of the target pest. Most beneficials will eat many different kinds of insects, but eating a few isn't control. Praying mantises, for example, feed on a wide range of pests but almost never serve to control outbreaks of any of them. In many instances, the beneficials will only give you partial control, so you may occasionally need sprays, too. Be careful to select a time and a material that will do minimal damage to the bugs you have bought.

Often the best strategy is simply to increase the biodiversity of your garden. "Simplify" an environment--by spraying an insecticide or by growing only one kind of plant--and problems get out of hand quicker. Make an environment more complex and problems are less likely. Accomplish this in your garden by planting a wide range of plants and by not using broad-spectrum insecticides.

Learning to use beneficial insects will make you a smarter gardener. Start by ordering some catalogs. Most suppliers provide some direction on how to use what they sell, although the quality of these details--and the prices--can vary greatly. Shop for quality as well as quantity. When you realize it's time to resort to the bug busters, it's often best to phone your order in. Most suppliers are very aware of the need to transport living cargo quickly and use express shipping when appropriate.

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