Wednesday, August 18, 2010
We don’t have a huge problem with insect pests. For certain pests, we sometimes use products such as insecticidal soap, which we make at home by mixing 2 tablespoons of baby shampoo to a quart of water and then transferring it to a spray bottle that we can spritz as needed.
But our favorite means of controlling pest insects is by letting predatory insects and other forms of wildlife dine on the problem pests.
There are days when dragonflies fill the air, performing beautiful aerial acrobatics as they swoop and dine on flying insects. We’ve put in a small pond near the house to help attract these flying exterminators and they do a great job during the few times a year when we see termites swarming on the edge of our wooded property.
For plant pests, our favorite insect predators are ladybugs.
I’ve loved ladybugs since I was a child. They are beautiful, gentle, almost storybook looking creatures and I would probably welcome them to my garden even if they weren’t beneficial.
But Ladybugs (also known as Ladybird beetles or lady beetles) are voracious predators, both as adults and in larval form. They help control aphids, scale, mealy bugs, spider mites and whiteflies, as well as other insects. Female lady beetles may lay from 20 to more than 1,000 eggs over a one to three month period, starting in spring or early summer. The tiny eggs are yellow & oval shaped and are usually found in clusters of 10-50, near aphid colonies. The eggs take 3-5 days to hatch and the larvae start chomping garden pests as soon as they hatch, consuming up to 400 aphids during this 29-day stage of their life.
Ladybugs live about 11 months as adults and can eat a whopping 5,000 aphids in their lifetime, in addition to the other garden pests they eat. Within a year, there can be as many as 5-6 generations of ladybugs. In the fall, adult ladybugs hibernate in plant litter and crevices, often at the base of a tree, along a fence or under a rock, where they find some protection from cold winter temperatures.
In theory, you’d think that if you have pest insects on your plants that ladybugs might just naturally find them. But that is rarely the case in our yard. Like the elusive hummingbird (another one of our garden favorites) ladybugs never really started to hang around until we made a concerted effort to attract them.
In addition to eating insects, ladybugs also need pollen and nectar to survive. So if you provide the plants that these beneficial insects prefer, you will have a much better chance of attracting and retaining them.
Beneficial insects are said to love tiny, fragrant flowers, especially those of herbs and vegetables. If you grow this type of plant, allow some of them to fully bolt and produce flowers. A variety of plants should be selected that bloom at different times of the year and for best results, these plants should be interspersed amid your other plants.
Plants that attract beneficial insects include: Alyssum, Angelica, anise, baby’s breath, bee balm, calendula, candytuft, caraway, carrot family, cilantro, clover, coreopsis, coriander, cosmos, daisy, Dill, evening primrose, fennel, feverfew, goldenrod, lavender, lemon balm, lovage, marigold, mint, mustard family, parsley, Queen Anne’s Lace, rue, spearmint, sunflowers, tansy, thyme, yarrow, and zinnias. Many of these plants can be grown inexpensively from seed (10 pkgs for $1 at many dollar stores and when on sale at Walgreens).
In addition to choosing plants with flowers to attract the beneficials, I have also heard about using “banker” plants. A banker plant is a plant chosen specifically to attract and host pest insects, which in turn will attract more beneficials.
I first learned about banker plants from Dr. Lance Osborne, a professor of entomology at the University of Florida who explained that “An ideal banker plant system utilizes a pest insect that does not hurt the crop or plant you are trying to protect but attracts the beneficial that will move off that plant and onto the other pests in your garden.”
Dr. Russell F. Mizell, III, another professor of entomology from the University of Florida, said that crape myrtles can be excellent banker plants.
“Crape myrtles attract an aphid which is host specific. In other words, it does not feed on any plants other than crape myrtles. However, the crape myrtle aphid and their sugar-laden honeydew serve as food for twenty or thirty species of beneficial predators as well as countless bees and wasps. Because the [crape myrtle] aphids are not native to the U.S., most of our native predators do not prefer these aphids over the native species. So the predators will leave the crape myrtles periodically to search the surrounding vegetation -- your yard and garden -- for their more preferred prey, your other plant pests, thereby, enhancing natural biological control. To be successful, you have to ignore the sooty mold and the aphids on the crape myrtles.”
Studies by universities and the USDA have shown that spraying plants with artificial insect attractants greatly increases egg laying of beneficial insects. Artificial food sources such as Wheast® are available for purchase from organic garden suppliers. Or you can make your own “fast food” for beneficials by mixing one part whey yeast (or brewer’s yeast) with one part sugar and 10 parts water and spraying the mixture on your plants. Plants should be sprayed when temperatures are below 80F. You extra "bug food" can be stored in a sealed container in the refrigerator for 7-10 days.
It should go without saying that if you want to attract ladybugs, and other beneficial insects, you should eliminate pesticides from your garden. Pesticides will hurt both the ladybugs and the insects that they feed on.
You can also purchase ladybugs at local garden centers and many online sources.
The first time I purchased and released live ladybugs, I had the experience that many people do: they all immediately flew away. This was despite the fact that I followed the suggestions to help retain them, such as watering the site before releasing the ladybugs (or releasing after a rain) and releasing the bugs in the evening, rather than the heat of the day. Another suggestion is to release only a few ladybugs at a time, over a period of about a week, instead of emptying the entire bag all at once. The rest can be stored in the refrigerator (NOT in an airtight container!) until their release. On severely infested plants, you can drape a thin sheet over the plant and release the ladybugs underneath.
I had better luck with Sta-Home Lady Beetles (1 pkg for $13.95 – enough to cover 1000 sq ft.) which I ordered from Gardens Alive, an online source for “Environmentally Responsible Products.” According to their advertisement, their ladybugs are ‘screened to remove parasitized bugs, they are ready to lay eggs, and they are hungry for pests.’ After releasing the ladybugs into my garden, I was quite impressed that many of them stayed around for weeks and even months. I did not do anything special to retain them, but I did have a plant that was well infested with aphids.
One Note: The Asian Ladybug
There are two types of ladybugs that can be found in our gardens: the native ladybugs species, Hippodamia convergens, and the Asian ladybug, Harmonia axyridis, which was imported into our country at the beginning of the 20th century to help reduce the populations of tree-killing aphids. If you decide to buy ladybugs, it is best to make sure you are getting the native species.
For more information:
Try Pesticide Alternatives (PDF File)
Where to buy ladybugs in Washington, DC