Bugs in the Garden – Good or Bad?

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All bugs serve an essential function in the ecosystem, even if it is difficult to sometimes see their immediate benefit. Some bugs decompose plants, giving us compost. Most are a food source for something higher up on the food chain.

Insects may eat plants or other insects. Generally speaking, beneficial insects are ones that feed on the pests of garden or landscape plants. Conserving these “good bugs” can lead to a healthy garden, where good bugs control bad bugs, so you don’t have to.

Many of the so-called good bugs are insects that hunt down other bugs. Examples of these predators include big eyed bugs, lacewings, and pirate bugs.

Some of these are cute creatures, which have made their way into pop culture, like the lady beetle. Others are strange looking, like the wheel bug, which is common in our area, so named for the raised area on its back that resembles a cogwheel. Its relative, the aptly named assassin bug, has a beak with which it stings and paralyzes prey.

There are also parasitic insects, which eat other bugs from the inside out. By definition, parasitism is a relationship in which one organism benefits and one is harmed.

One of the most common parasitic insects in the garden is the braconid wasp, which makes small, white, capsule shaped cocoons on caterpillars. Tomato hornworms, which can be pests of gardens, are often found with these cocoons on their bodies. The wasp eventually kills the caterpillar by digesting its insides.

There are also parasitoids, insects with larvae that are parasitic. A common example of this in the garden is Aphidius wasps. (These wasps are very small and don’t sting humans like their larger cousins.) Aphidius wasps sting living aphids, common plant pests, and lay their eggs inside the aphid’s body. While inside the aphid, the wasp egg hatches into a larva. As the larva develops, it kills the aphid from the inside out. Then the wasp larva matures into an adult, chews a hole through the aphid’s body, and emerges to start the process all over again.

If parasitized hornworms or aphids are found in the garden, leave them alone, so that the parasitic insects can establish a population. Although the term parasite usually has a negative connotation, in this case parasitism can be beneficial, at least to gardeners.

To conserve beneficial insects in the garden, avoid killing them. Make sure that insects in the garden are actually pests before deciding to treat them. Depending on the pest, picking them off and killing them may be the best option.

For more information on beneficial insects, visit http://go.ncsu.edu/nqpkld. For answers to your garden or landscape questions, contact the Caldwell County Extension Service at 828-757-1290 or visit caldwell.ces.ncsu.edu.