Q. Is it practical to purchase and release beneficial insects to help control pests in my yard and garden? I try to avoid pesticides, but when the bad bugs are causing too much damage, I feel like I should do something.
A. There are numerous insects that can be considered "beneficial" in that they are predators or parasitoids of pest insects. Predators feed on various life stages of insect pests, while parasitoids live in or on them, eventually killing the pest. Unless you regularly use broad-spectrum insecticides, they already are more active in your garden than you realize.
Everyone recognizes lady beetles and praying mantises, but few are aware of the most effective beneficial insects. These include parasitic wasps, some of which are smaller than the period at the end of this sentence. Still others are parasitic flies that resemble houseflies. You may have even swatted a few of them, thinking that they were nuisance pests. Ground beetles look fierce and may be mistaken for bad guys, but they are important predators of many pests, including gypsy moth larvae and many soil-dwelling insects. Adult flower flies may be mistaken for yellow jackets, but they do not sting; their larvae are voracious aphid predators.
Many species of beneficial insects are available commercially and are becoming increasingly popular to help control pests in greenhouses. The U.S. Department of Agriculture, in conjunction with agricultural research stations, has introduced predators and parasites of foreign pests that were accidentally introduced into this country. These include tachinid flies that are parasites of gypsy moths, twice-stabbed lady beetles that are predators of euonymus scale, and vedalia beetles that are predators of cottony cushion scale on citrus.
While buying and releasing beneficials can help control large populations of insect pests, a better approach in the home garden is to attract and encourage existing populations. The most important thing you can do to protect and encourage beneficial insects in your garden and landscape is to choose insecticides with care. Many beneficials are more sensitive to insecticides than the pests you are trying to control.
While it is true that beneficials can reduce your pesticide use, realistically you will still have to use pesticides to deal with serious pest outbreaks from time to time. The key is to choose products that have little or no residual activity. While the beneficials present when you spray will be killed, new ones coming into your garden will not be affected. These insecticides include insecticidal soap, horticultural oil and botanical insecticides such as neem, pyrethrins, rotenone and sabadilla. The botanicals do have brief periods of residual activity, but they are much shorter than most synthetic insecticides. Most break down rapidly when exposed to the sun.
It is also important to have as much diversity as possible in your plantings. A mix of trees and shrubs, grass (yes, low-maintenance turf is an important habitat for some beneficials), and annual and perennial flowers is best. Permanent plantings such as trees, shrubs and turf provide a place for beneficial insects to overwinter. The adults of many beneficials feed primarily on pollen and nectar, so it is important to have something in bloom from early spring until late fall. Some of the best flowers for attracting beneficials include the following families:
Carrot family (Apiaceae): Plants in the carrot family are especially attractive to small parasitic wasps and flies. Interplant them in your vegetable garden and flower beds. Plants include: caraway (Carum carvi), coriander/cilantro (Coriandrum sativum), dill (Anethum graveolens), fennel (Foeniculum vulgare), Bishop's flower (Ammi majus), Queen Anne's lace (Daucus carota), and toothpick ammi (Ammi visnaga).
Aster family (Asteraceae): attractive to larger predators such as lady beetles and soldier beetles. Incorporate into vegetable garden and flower beds. Includes: blanketflower (Gaillardia spp.), coneflower (Echinacea spp.), coreopsis (Coreopsis spp.), cosmos (Cosmos spp.), golden marguerite (Anthemis tinctoria), goldenrod (Solidago spp.), signet marigold (Tagetes tenuifolia), sunflower (Helianthus spp.), tansy (Tanacetum vulgare), and yarrow (Achillea spp.).
Legumes (Fabaceae): generally grown as cover crops and attractive to many beneficials. Includes: alfalfa (Medicago sativa), fava bean (Vicia fava), hairy vetch (Vicia villosa), and sweet clover (Melilotus spp.).
Mustard family (Brassicaceae): attractive to beneficials that are parasites and predators of insect pests of the mustard family (broccoli, Brussels sprouts, cabbage, cauliflower, kohlrabi, mustard greens). Plant these away from the garden rather than in the garden because these plants attract pests and beneficials. Some are common weeds, such as yellow rocket and wild mustard. Plants in this family include basket-of-gold alyssum (Aurinia saxatilis), mustards (Brassica spp.), sweet alyssum (Lobularia maritima), yellow rocket (Barbarea vulgaris), and wild mustard (Brassica kaber).
Verbena family (Verbenaceae): attractive to a variety of beneficial insects. Many plants in this family are favorite garden flowers, including lantana (Lantana camera), Buenos Aires verbena (Verbena bonariensis), hybrid verbena, and lilac vervain (V.rigida).
Beneficial insects also need water. Shallow containers such as ceramic pot saucers with pebbles for them to rest on are best.
The following books and websites have information on beneficial insects as well as good pictures to help you identify them.
"Controlling Vegetable Pests" by Pamela Pierce, Ortho Books, 1991.
"Insects That Feed on Trees and Shrubs" by Warren Johnson and Howard Lyon, Cornell University Press, 1991.
"Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control" by Mary Louise Flint and Steve Dreistadt, University of California Press, 1999.
Biological Control: A Guide to Natural Enemies in North America: www.biocontrol.entomology.cornell.edu/index.php
Midwest Biological Control News: www.entomology.wisc.edu/mbcn/
Nematodes as Biological Control Agents of Insects: http://nematode.unl.edu/wormepns.htm
The Pennsylvania IPM Program: http://extension.psu.edu/ipmgarden
Send questions to Sandy Feather by email at firstname.lastname@example.org or regular mail c/o Penn State Extension, 400 N. Lexington Ave., Pittsburgh 15208.