There are approximately 250,000 insect species in the U.S., with 30,000 of these living in Texas. That’s more insect species than all the kinds of birds, mammals, reptiles, fishes and plants combined. We are continually surrounded by insects, both in and around our homes.
Insects have a bad rap since the most familiar ones are the ones that bug us. Some insects can do considerable damage to crops; others are vectors of serious diseases. But, did you know that only 3 percent of the 250,000 species are classified as economic pests? However, there are more than twice as many beneficial insects (7 percent), those that are either predators or parasites of pest insects, or pollinate our flowers, vegetables and fruit. That leaves about 90 percent that are just part of the web of life, providing food for animals or helping decompose various types of organic matter, both vegetable and animal.
So, the saying, “The only good bug is a dead bug” is not true! Our gardens are filled with good bugs, and you should learn to recognize these gardening friends and take steps to preserve and encourage the “good guys” to make your garden their home. Not every insect on your plants is a threat needing to be eliminated. Usually they are one of the 90 percent that just happen to be there; and sometimes they are there helping out our gardens.
Paper wasps are feared by many because of their painful stings. But, they are also very important by feeding on caterpillar pests.
Often beneficial insects are so small it is difficult to find them, even if you know what to look for. But they are out there working for you.
If you find true garden pests on your plants, such as aphids, caterpillars, spider mites or thrips, first consider whether the pest population is large enough and doing serious damage to warrant treating with a pesticide. Next, look for beneficial insects that may be present.
Aphids can quickly build up large numbers on young tender shoots, but often a large aphid population is brought under control after a few days by a number of “good guys” including lady beetles, lacewings, and syrphid fly larvae.
So, look for aphid mummies with little holes in them. If you find them, then let nature do the work for you instead of spraying with an insecticide that would not only kill the aphids, but also the good guys working for you. The trouble is that the aphid population can rebound much faster than the good guys because aphids are born pregnant, reproducing faster than rabbits.
If you find you do need to use a pesticide, select one that is specific for the target pest. Broad-spectrum insecticide can kill both the target pest and beneficial insects. A good example of this is spraying tomatoes. Carbaryl (eg. Sevin), a common insecticide, kills beneficial mites that effectively keep spider mite populations under control. Many times tomatoes with the worst mite problems are those which are routinely sprayed with insecticides, whether needed or not.
Certain plants attract beneficial insects, and can be planted to help maintain a population of the “good guys”. Plants with flat flower heads, including yarrow, anise, dill and fennel, or daisy flowers like chamomile and ox-eye daisy, along with salvias and other flowering herbs all help attract beneficial insects.
The Tropical or Mexican Milkweed (Asclepias curassavica) is a great plant for building up a population of insects that feed on aphids. This is because yellow aphids are attracted to tropical milkweed like a magnet, but don’t feed on most other landscape plants. There you can find all kinds of aphid predators that will also feed on aphids in other parts of your garden, along with monarch butterflies who also relish the nectar-rich flowers.
Successful gardeners provide optimum growing conditions for each plant in the garden. The best tool is the your own shadow in the garden and landscape. This enables you to quickly spot unusual symptoms on your plants early on. When pest or damage appears, good gardeners try to figure out what is causing the problem, and whether or not the damage serious, is on the increase or is liable to correct itself without pesticides .
Learn to identify beneficial insects in all stages of their life cycles. Also, learn what parasitized aphids and caterpillars look like.
Keith Hansen is Smith County Horticulturist with the Texas AgriLife Extension Service.