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How to Attract Beneficial Insects to Control Garden Pests


Syrphid fly larvae eat aphids by the dozens.

Syrphid flies, also called hover flies, are good pollinators. Their larvae eat aphids by the dozens.

Photo: Flickr user Gilles Gonthier

As a gardener, there's nothing more frustrating than finding a prized vegetable crop being devoured by insect pests. A couple of hornworms can level a row of tomatoes overnight. Fortunately, every pest has a predator, and we can use that natural food chain to our advantage. A sufficient number of beneficial insects will keep garden pests to manageable numbers. You just have to know how to attract those beneficial insects to your garden.

Beneficial Insects, Nature's Pest Control:

Put simply, a beneficial insect is an insect (or other arthropod) that helps you grow healthy plants. Some insects prey on other arthropods, eating pests like aphids and beetles. Other beneficial insects parasitize pests, eventually killing them. And still other insects help the gardener by pollinating crops, insuring a good harvest. Ideally, you should try to attract all three kinds of beneficial insects to your garden – predators, parasitoids, and pollinators.

Don't Use Pesticides in Your Garden:

Pesticides can't distinguish the good guys from the bad guys. You're trying to attract more insects to your garden, not kill them all, right? When you find your broccoli smothered in aphids, or your squash covered in beetles, you might be tempted to reach for a chemical control. Don't do it!

When you're first trying to attract beneficial insects to your garden, you may find the pest population skyrockets for a bit. Be patient. You have to give the good bugs time to find the smorgasbord. The lady beetles will find your aphids, mate, lay eggs, and soon be picking your broccoli clean. As long as they've got food to eat, the beneficial insects will stay put once they've arrived. Don't send them packing by spraying toxic chemicals.

Plant an Insectary to Invite Insects to Your Garden:

An insectary is a garden plot just for the insects. The right variety of plants will attract beneficial bugs to the neighborhood. It can be a separate landscape bed right near your garden, or several small plantings interspersed among the veggies.

So what do you plant in an insectary? First, plant some early bloomers to attract beneficial insects early in the season, even before your crops are full of pests. Many of the important beneficial insects, like hover flies and lacewings, feed on pollen and nectar as adults. By providing flowers early in the season, you will invite these insects into your garden in time to unleash their predatory offspring on your aphids and mites.

The insectary should include plants of varied heights. Low growing herbs like thyme and oregano give ground beetles a place to hide. Taller flowers, like daisies or cosmos, beckon to hover flies and parasitic wasps looking for nectar. Praying mantids will hide between the plants in a well-planted insectary.

Umbels and composite flowers provide the most attractive sources of food to most beneficial insects. The tiny, clustered flowers of umbels offer exposed nectar and pollen to smaller pollinators like parasitic wasps. This group includes yarrow, dill, fennel, and wild carrots. Composites attract the larger pollinators, like robber flies and predatory wasps. Composite flowers include many garden favorites, like zinnias and sunflowers.

Provide Water for Insects:

Like all animals, insects need water to live. If you use a sprinkler to water your garden, the puddles that form will suffice to give bugs a drink. Between waterings or if you use a drip irrigation system, the insects will need another source of water. Make a simple watering hole with a saucer and some rocks, and keep it full on dry days. Remember, most of these insects have wings, and will fly away if they can't get what they need nearby.

Give the Ground Dwellers Some Cover:

Some beneficial insects stay down on the ground, searching for soil-dwelling pests. Ground beetles, for example, rarely climb the plants looking for pests to eat; instead, they patrol the soil at night, munching on slugs and cutworms. During the day, these nocturnal minibeasts need some shelter from the bright sun.

Keep your garden beds mulched, so ground beetles and other earth bound insects can burrow during the day. The mulch will also keep the soil moist, and help the beneficial bugs from drying out. Use stepping stones on garden paths. Many insects love to hide under boards or flat stones when they aren't hunting pests.

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