This piece first appeared in the Winter 2009 Issue of Master Gardener Magazine; www.mastergardeneronline.com
Did the bugs do a number on your garden plants this past growing season? Did they chomp up the leaves of a special plant or suck the life out of your roses? Regardless they took some of the joy out of your garden.
In the days before environmentally friendly gardening became the norm, this would have meant getting out the chemicals and spraying the heck out of everything in the garden. The bad bugs usually died off but unfortunately so did all the rest of the good bugs.
We have grown wiser in the last couple of decades and have begun to recognize that the beneficial predator insects are allies in the effort to keep detrimental bugs in check. A garden full of predator insects means you have an unbeatable crew of garden clean-up artists who, for little more than food and shelter, are on the job 24/7 during the growing season.
All you have to do is learn what they need and adapt your gardening methods to help them thrive.
Who are Some of the Good Guys
Just what are beneficial predator insects? They are insects and their larvae who find that bugs like aphids, thrips, mealy bugs, spider mites, scale, and soil organisms including slugs make tasty snacks or are a good place to lay eggs. Often their activity is on such a small scale that you don’t know they are out there working. The lack of aphids or thrips in the garden doesn’t mean they aren’t there. It may mean that the predator insects got to them before they did major damage to your plants.
Lady beetles or bugs are small red-orange insects with black markings. The larvae are black with yellow markings and are found crawling on plants. The adults will fly short distances between plants. Both the adult and larvae stage will eat aphids, scale insects, spider mites and mealy bugs.
Lacewings are brown or green with lacey clear wings. They are found flying around plants. They and their larvae, known as aphid lions, prey on scale insects, mealy bugs, whiteflies, caterpillars, leafhoppers and thrips. Beetles such as solider, tiger, ground and rove inhabit leaves, flowers and seeds or spend their time on the ground foraging for soil organisms. Some fly while others run very quickly over the plants and ground. They generally eat slugs, snails, cutworms, root maggots and Colorado Potato beetles.
True bugs from the Hemiptera family including assassin, ambush, big-eyed, minute pirate, damsel and predacious stink bug are often found at various levels of vegetation and feed on a general list of other insects they encounter. Pirate bugs in particular go after thrips, mites, scale, aphids, and whiteflies.
Predacious hoverflies and parasitoid tachinid flies are both members of the Diptera family. Hoverfly adults mimic bees and wasps in appearance and manner but are smaller, fly more quickly and will hover around flowers. The larvae look like small maggots that prey on aphids and scale insects. The adults feed on insects they find feeding on flowers. Hoverflies are active early in the season before many other predators are out.
Tachinid flies can resemble house and blow flies and are found near flowers looking for hosts for their eggs. They lay eggs on worms, beetles, sawflies and other bugs. The larvae enter the host to feed before pupating outside the host, killing it in the process.
Wasps are an important group of predator insects and the group most likely to run into a conflict with humans. Thread-waist wasps, yellowjackets and hornets are all meat eaters that will eat a variety of insects they find in the garden. Adults will bring masticated insects back the young in their hives. Being opportunists, they often don’t see much difference between the bugs and the burgers or fish on the picnic table.
Parasitic wasps are tiny in comparison with larger wasps. They are found around flowers where they seek out cutworms, corn earworm, horn worms, gypsy moths, leafrollers, cockroach eggs and beetles to lay their eggs in.
Attracting Them to Your Garden
Encouraging predatory beneficial insects to take up residence in your garden involves creating a balance between the beneficial insects and the detrimental bugs and providing the right food, shelter and breeding environments.
One of the first things many gardeners have to do is change their mind set. Many of us see bugs on our plants or find damage and immediately think we have to get rid of the offenders. In the bad old days that meant grabbing the spray and nuking everything in sight. In this new environmentally friendly era, this means learning to live with a few detrimental insects to keep the beneficial insects around the garden. In agriculture this is often referred to as the economic threshold and represents the point at which the populations of detrimental bugs begin to make more of an impact on the crop than the farmer is willing to accept.
For the home gardener, this means determining what level of damage he or she is willing to tolerate before their enjoyment of the garden is reduced to an unacceptable level. This enjoyment threshold will be very different for every gardener. If the environment is favorable, the populations of beneficial predators and detrimental insects will ebb and flow. The detrimental insect populations will grow and a few weeks later the predator populations will expand to take advantage of the abundant food source. The detrimental insect population then shrinks and the cycle begins again.
Creating an Insectary for Beneficial Insects
Beneficial insects are no different than other wildlife in the garden. To survive they need a relatively undisturbed place in the garden with adequate food sources, access to water, shelter from the elements and their predators and places to lay eggs. While they eat other bugs, many predator insects also need pollen for protein and nectar for the carbohydrates provided by flowering plants. A group of such plants is called an insectary.
Insectaries are usually groupings of preferred plants such as blooming annuals, perennials, shrubs and trees where the insects can live undisturbed and venture to other parts of the garden to feed and mate. Research has shown that the most effective way to create the proper environment is to plant preferred plants in either blocks around the garden or in hedgerows along a property line or a lightly used part of the yard. These groupings or hedgerows then need to be maintained with the insects in mind.
Living with a few weeds may also help draw beneficial insects because some of them are a highly favored source of pollen and nectar. Dandelions are a good source of food early in the spring before some detrimental insects fully emerge. Plants in the insectary need to be of varying heights and densities to give insects a flexible habitat. Some insects live near the top of plants while others like ground beetles live near the soil and need the protection of dense cover. Others like lacewings lay their eggs in shady, protected areas in dense foliage.
The best flowers to plant for beneficial insects are those with small flowers in large clusters. Because many of the beneficial insects are small, a small flower is easy to get into to get pollen and nectar. The small insects can actually drown trying to get into large flowers. Flower clusters that are flat or composed of single petals also make good landing places and places to search out a mate.
There needs to be something blooming in the insectary from early spring to late in the fall. Because the beneficial insects are out as long as the detrimental insects are active, they need access to food sources throughout the season. Research has also shown that providing a variety of flowering plants not only sustains adult beneficial insects but also allows longer survival periods and higher breeding rates
While there are dozens of plants that the beneficial insects like, three families of plants in particular are very popular with the beneficial insects. In any case, it is important not to plant noxious weeds or other invasive species. Be sure to check your state’s noxious weed lists first.
The Apiaceae or carrot family (formerly the Umbelliferae) is comprised of more than 3,000 species of plants many of which are very familiar to us. The family includes common culinary favorites such as carrots, parsley, coriander, dill, fennel (invasive in western Washington), parsnips, cumin and garden plants such as sea holly, lovage, angelica and wild carrot. The Apiaceae is characterized by flat topped flowers held up on hollow stems. The flowers are a mass of smaller individual florets that the beneficial insects find very easy to get nectar and pollen from and are an easy place to land.
The Brassicaceae or mustard family (also known as the Cruciferae) is another large group of plants beneficial insects find attractive because of their small but abundant flowers. Culinary members of the family include broccoli, Brussels sprouts, cauliflower, cabbage, turnip, rapeseed (canola), horseradish, Chinese cabbage and others. Herbaceous members of the family include bittercress, alyssums, tumble mustards and arabis. Vegetable gardeners wanting to encourage beneficial insects should let a few broccoli plants flower to attract them.
The third family is the Asteraceae which includes asters, sunflowers and daisies. Gardeners prize members of this family for their color and bloom periods that starts in mid summer and goes well into the fall; perfect for keeping beneficial insects around late in the season. The flowers are a composite flower made up of rays of ray-shaped petals around a center of tiny disk flowers.
If all your plantings work, you should be able to attract native populations of beneficial insects to your garden. Sometimes however, there aren’t enough around or you need a large quantity to go after a particular pest. Beneficial insects can be purchased from garden centers or online from several sources. Local garden centers are likely to have the most popular varieties while the online sources will have a broader selection. Remember the insects are alive and will need to be deposited in the garden immediately after delivery or purchase. Read the instructions carefully so that you put them in the right place in the garden.
The bugs will disperse around the garden on their own and a few will venture away from it. There is no way to keep them in one place especially if there isn’t enough food or if they are wanderers by nature. Lady bugs are notorious for this but they will set up shop somewhere close and be back when conditions are right.
Beneficial predator insects are a great ally in the garden especially when they are on the job 24/7. Adapting our gardens and our perspective is a small change to make to encourage them to establish themselves.
Flowers used by beneficial insects
Source: Colorado State University Cooperative Extension.
All plants on this list will grow state-wide.
Early Season Blooming
- Basket of gold (Aurinia saxatilis)
- Rocky Mountain penstemon (Penstemon strictus
- Creeping thyme (Thymus praecox)
- Sweet alyssum (Lobularia maritima)
- Columbine (Aquilegia x hybrida) – look for native species Aquilegia formosa
- Carpet bugle (Ajuga reptans)
- Common yarrow (Achillea filipendulina ‘Coronation Gold’)
- Dwarf alpine aster (Aster alpinus)
- Spike speedwell (Veronica spicata)
- Wine cups or poppy mallow (Callirhoe involucrata)
- Cilantro or coriander (Coriandrum sativum)
- English lavender (Lavandula angustifolia)
- Edging lobelia (Lobelia erinus)
- Stonecrop (Sedum species)
- Lavender globe lily (Allium tanguticum)
- Dill (Anethum graveolens)
- Dyers chamomile (Anthemis tinctoria)
- Sea lavender (Limonium gerberi)
- Wild bergamot (Monarda fistulosa)
Attracting Beneficial Insects to Your Garden http://www.grinningplanet.com/2005/04-26/beneficial-insect-natural-pest-control-article.htm
Plants for Pollinators in Oregon
A Pocket Guide to Common Pests of Crops and Gardens in the Pacific Northwest
Washington State Noxious Weed List – 2008
USDA Plants Database – Good source of natives of some of the plants listed in Plants List.
Sources of Beneficial Insects
P.O. Box 8910
Tucson, AZ 85738-0910
P.O. Box 87
Mathis, TX 78368
5100 Schenley Place
Lawrenceburg, IN 47025
M & R Durango
P.O. Box 886
Bayfield, CO 81122
8864 Little Creek Dr
Orangevale, CA 95662
P.O. Box 35
Medford, OR 97501
P.O. Box 1555
Ventura, CA 93002