Biological Controls

Establishment of Beneficial Organisms

Ladybugs (Family Coccinellidae)
Lacewings (Families Chrysopidae and Hemerobiidae)
Praying Mantis (Family Mantidae)
Trichogramma Wasps (Family Trichogrammatidae)
Ichneumon Wasps (Family Ichneumonidae)
Tachinid Flies (Family Tachinidae)
Mites (Phytoseiidae and Others)
Mosquito Fish (Gambusia affinis)

Use of Pathogenic Bacteria

Establishment of Toads and Frogs
Use of Beneficial Nematodes
Use of Limonoid Sprays
Use of Liquefied Pest Sprays
Use of Resistant Varieties
Interplanting with Plants That Produce Natural Insecticides or Substances Offensive to Pests

Weeds

Table 1: Specific Weeds and the Agents Involved in Their Biological Control

Insects

Table 2: Specific Biological Controls for Several Types of Insect Pests

Table 3: Companion Plants

If you were to ask the average farmer or backyard gardener how to control a particular insect or plant pest, you might be given the name of some poisonous spray or bait that has proved "effective" in the past. However, evidence that spraying with such substances yields only temporary results has been mounting for many years, and the spraying is frequently followed by even larger invasions of pests. Also, the residues of poisonous sprays often accumulate in the soil and disrupt the microscopic living flora and fauna essential to the soil's health. The problem is compounded and the ecology further upset when large amounts of inorganic fertilizers are added. As increasing numbers of people become aware of the devastating effects on the environment of pesticides and herbicides, they have been turning to biological controls as an alternative to the use of poisonous sprays. To the surprise of some, such controls are often more effective than traditional controls.

Poisonous sprays often promote pest invasions because the sprays usually kill beneficial insects along with the undesirable ones. In addition, the pests, through mutations, often become resistant to the sprays. In undisturbed natural areas, weeds are never a problem, and even though pests may be present, they seldom destroy the community. Why is this so? You may recall from your reading that all members of a community are in ecological balance with one another. The plants produce a variety of substances that may either repel or attract insects, inhibit or promote the growth of other plants, and generally contribute to the health of the community as a whole.

Virtually all insects have their own pests and diseases, as do most other living organisms. Each pest ensures, at least indirectly, that the various species of a community are perpetuated. This principle of nature can be applied, to a certain extent, to farming and gardening. Following are some general and specific biological controls that are currently either in widespread use or undergoing testing and showing promise for the future.

The small and often colorful beetles called ladybugs, particularly their larval stages, consume large numbers of aphids, thrips, insect eggs, weevils, and other pests. They are obtainable from various commercial sources (e.g., Planet Natural, P.O. Box 3146, Bozeman, MT 59772 (1-800-289-6656 or http://www.planetnatural.com/); Nature's Way Organics, P.O. Box 228, Rimrock, AZ 86335 (1-800-493-1885). However, if given a chance, ladybugs will probably establish themselves without being imported. When obtained from outside the local area, they should be placed in groups at the bases of plants on which pests are present, preferably in the early evening after watering.

Lacewings are slow-flying, delicate-winged insects that consume large numbers of aphids, mealybugs, and other pests. They lay their eggs on the undersides of leaves, each egg being borne at the tip of a slender stalk. The larvae consume the immature stages of leafhoppers, bollworms, caterpillar eggs, mites, scale insects, thrips, aphids, and other destructive pests. Commercial sources include: Nature's Way Organics, P.O. Box 228, Rimrock, AZ 86335 (1-800-493-1885); All Pest Control, 6030 Grenville Lane, Lansing, MI 48910.

About 20 species of praying mantis are now established in the United States. These are voracious feeders that prey somewhat indiscriminately on flying insects, and sometimes even on other mantises. They can be established by tying their egg cases to tree branches or other locations above the ground. The egg cases, which form compact masses about 2.5 to 5.0 centimeters (1 to 2 inches) long, are obtainable from various commercial sources, including: Peaceful Valley Farm Supply, P. O. Box 2209, Grass Valley, CA 95945; Planet Natural, P.O Box 3146, Bozeman, MT 59772 (1-800-289-6656 orhttp://www.planetnatural.com/).

Trichogramma wasps are minute insects, usually less than 1 millimeter (1/25 inch) long; they parasitize insect eggs and are known to have significantly reduced populations of well over 100 different insect pests, including alfalfa caterpillars, armyworms, cabbage loopers, cutworms, hornworms, tent caterpillars, and the larvae of many species of moths. As with other insects used as biological controls, trichogramma wasps should not be released unless there are pest eggs in the vicinity, since the wasps may otherwise parasitize the eggs of beneficial butterflies and other useful insects. They are available from commercial sources such as: Unique Insect Control, P.O. Box 15376, Sacramento, CA 95851; New Earth, 4422 East Hwy. 44, Shepherdsville, KY 40165.

The ichneumon wasps belong to a very large family of wasps that are mostly stingless. These tiny wasps tend to be slender and have long ovipositors that are sometimes longer than the body. Most insects are parasitized by at least one species of ichneumon; many species parasitize the larval stages of insects, consuming the host internally after hatching from eggs deposited on the body; alternatively, they may complete development in a later stage. Ichneumons usually appear naturally in a backyard or farm population of pests if toxic sprays and other unnatural conditions have not interfered with their normal activities.

Many members of the large family of tachinid flies resemble houseflies or bumblebees. All parasitize other insects, including a large variety of caterpillars, Japanese beetles, European earwigs, grasshoppers, gypsy moths, tomato worms, sawflies, and various beetles. Contact Mad Planter Beneficials at 1-800-548-8199 for further information.

Species of several genera of mites prey on red spider mites and have been used successfully to control other mites and scale insects.

Mosquito fish have been added to bodies of fresh water all over the world to control mosquitoes. The fish feed on mosquito larvae, particularly as the larvae rise to the surface for air. One mosquito fish can consume thousands of larvae per day.

Bacillus thuringiensis (BT) is one of several pathogenic bacteria registered for use on edible plants in the United States. It reproduces only in the digestive tracts of caterpillars and is harmless to humans and all other wildlife, including earthworms, birds, and mammals. It is exceptionally effective against a wide range of caterpillars, such as tomato hornworms and fruitworms, cabbage worms and loopers, grape leaf rollers, corn borers, cutworms, fall webworms, and tent caterpillars. It is mass-produced and sold in a powdered spore form at nurseries and garden supply stores under the trade names of Dipel, Biotrol, and Thuricide. The powder is mixed with water and applied as a spray. Beneficial bacteria are available from Solutions Unlimited, Sharon Springs, NY 13459.

It has been estimated that a single adult toad consumes about 10,000 insects and slugs in one growing season. Toads and frogs feed at night when snails, slugs, sowbugs, earwigs, and other common pests are active.

Several species of nematodes, which are abundant microscopic roundworms, are notorious for damaging economically important crops when they invade plant roots and other underground organs. Most species, however, are either harmless or beneficial to plants. They have been used successfully in parasitizing cabbage worm caterpillars and codling moth larvae, Japanese beetle grubs, and tobacco budworms. They have shown considerable potential against other pests as well. One species that has been particularly effective in controlling ants, beetles, bugs, flies, wasps, and many other insects is the caterpillar nematode (Neoaplectana carpocapsae). It carries a symbiotic bacterium (Xenorhabdus nematophilus), which multiplies rapidly in the host, killing most insects within 24 hours after initial contact. It may be obtained from Nematode Farm, Inc., 2617 San Pablo Avenue, Berkeley, CA 94702.

Limonoids are bitter substances found in the rinds, seeds, and juices of citrus fruits (especially grapefruit). After grinding up the rinds and seeds of two or three fruits, soaking this substance overnight in a pint of water, and then straining out the solid material, the resulting liquid may be sprayed on plants. The bitter principle apparently stops or reduces the feeding of larvae on the foliage. In experiments, limonoid sprays have proved effective against corn earworm, fall armyworm, tobacco budworm, and pink bollworm, but undoubtedly will deter many other pests as well.

Jeff Cox, an editor of Rodale'sOrganic Gardening, called attention to this method of pest control in the magazine in October 1976 and again in May 1977. Insect pests or slugs are gathered in small quantities and liquefied with a little water in a blender. The material is then further diluted with water and sprayed throughout the infested area. It is not known why spraying with "bug juice" is effective against pests. However, it is known that virtually all organisms harbor viruses. Thus, it has been theorized that even the inactive viruses carried by healthy insects and slugs may somehow be activated in the process of liquefaction. The viruses would be spread throughout an entire yard or farm if all parts of the area were sprayed. Most viruses are highly specific, generally attacking a single species of organism. M. Sipe, a Florida entomologist who recommended the "bug juice" technique, also suggested that the odor of the liquefied insects possibly attracts their predators and parasites or that the insects' distress pheromones (naturally produced insect chemicals that influence sexual or other behavior) are released by the blender, with the pheromones acting as an insect repellent. Possibly the observed effects of spraying "bug juice" are the result of a combination of viruses, predator attraction, and repellent pheromones. Sipe warns that a person who tries this method of pest control should take care to use only pest species and only those that are doing significant damage. Failure to heed this warning could disrupt the activities of the natural predators and other natural controls present. This approach needs extended testing and investigation of its safety for use by humans, but test results over the past twenty years in various areas of North America have yielded impressive results with no evidence of harm to either humans or beneficial organisms.

Many plants may kill or inhibit disease fungi or bacteria with chemicals known as phytoalexins. Phytoalexins are synthesized at the point of attack or invasion by the pathogen and are toxic to the fungus or bacterium. In selecting for improved fruit quality, vigor of growth, or other desirable characteristics, horticulturists in the past have sometimes unknowingly bred out a plant's capacity to produce certain phytoalexins, although general vigor is usually accompanied by disease resistance. Now that this aspect of a plant's defense mechanisms is known, breeders are concentrating on developing varieties capable of producing phytoalexins against various fungi, bacteria, and even nematodes. Several tomato varieties, for example, are listed as being VFN. The letters V and F indicate a resistance toVerticilliumandFusarium (common pathogenic fungi), while the letter N denotes a resistance to root-knot nematodes.

Other aspects of plant disease resistance include thick cuticles; the secretion of gums, resins, and other metabolic products that may interfere with fungal and bacterial spore germination; and the presence within all the plant’s cells of chemical compounds toxic to pathogens.

Many plant species produce substances that repel a significant number of pests, but none produce anything that repels all pests. Among the best-known plant producers of insect repellents are marigolds, garlic, and members of the Mint Family, such as pennyroyal, peppermint, basil, and lavender. An expanded discussion of this subject is given in Useful Plants and Poisonous Plants.

In 1974, the Weed Science Society of America published a special committee report (Weed Science 22:490-95) on the biological control of weeds, summarizing the status of projects on the biological control of weeds with insects and plant pathogens in the United States and Canada.Table 1 is condensed from that report and supplemented with additional information. Many other biological controls for these and other weeds are currently under investigation.

The maintenance of ecological balance in nature includes a vast array of predator-prey relationships between animals, birds, insects, and other organisms. Specific biological controls for several types of insect pests, in addition to the general controls previously discussed, are given inTable 2.

The Additional Reading on Biological Controls list reveals that the literature on the chemical interactions between plants and also between plants and their consumers is already extensive. However, despite the scientific evidence on the subject to date, a significant amount of the "backyard biological control" that is practiced today is based primarily on empirical information. Such information has been obtained from thousands of gardeners and farmers who have tried various techniques with their plantings and pest controls. As a result, they have come to conclusions that certain things work while others do not, but they have not deliberately set up controlled experiments, nor have they necessarily understood the scientific basis for what they have observed. This does not mean that their observations are not useful or that they are invalid. In fact, such empirical observations have often been the inspiration for investigations and experiments by scientists. Although the scientific investigations have sometimes revealed that the empirical observations were biased or not carefully made or that erroneous conclusions were drawn, sound scientific bases for these observations have frequently been uncovered. Further insights into how plants inhibit or enhance the growth of others and the nature of their resistance to disease or insect-repelling mechanisms continue to be discovered.

Observations of such phenomena in the past have led organic gardeners and others to practice companion planting, which involves the interplanting of various crops and certain other plants in such a way that each species derives some benefit from the arrangement.Table 3 is a list of combinations of vegetables, herbs, flowers, and weeds that are mutually beneficial according to empirical information, primarily from current reports of organic gardeners and companion planting traditions. This list appeared in the February 1977 issue ofOrganic Gardening and Farming magazine and is included here with the permission of Rodale Press, Inc.

• China Herb Co., 428 Soledad, Salinas, CA 93901
• Cottage Herbs, P.O. Box 100, Troy, ID 83871
• De Giorgi Co., 6011 N St., Omaha, NE 68117
• Fragrant Fields, Dongola, IL 62926
• Herbs-Liscious, 1702 S. Sixth St., Marshalltown, IA 50158
• Hsu's Ginseng Enterprises, P.O. Box 509, Wausau, WI 54402
• Jude Herbs, Box 56360, Huntington Station, NY 11746
• Otto Richter and Sons, Box 260, Goodwood, Ontario, LOC 1A0
• PG Nursery, R18, Box 470, Bedford, IN 47421
• Putney Nursery, Putney, VT 05346
• Rawlinson Garden Seed, 269 College Rd., Truro, Nova Scotia B2N 2P6
• Sanctuary Seeds, 2388 West Fourth Avenue, Vancouver, British Columbia V6K 1P1
• Sea Island Savory Herbs, 5920 Chisolm, John's Island, SC 29455
• Shoestring Seeds, P.O. Box 2261, Martinsville, VA 24113
• Story House Herb Farm, Route 7, Box 246, Murray, KY 42071
• Sunnybrook Farms Nursery, Box 6, Chesterland, OH 44026
• Sunshine Herbs and Flowers, Rt. 1, Box 234, Comer, GA 30629
• The Thyme Garden, 20546-0 Alsea Hwy., Alsea, OR 97324
• Thompson and Morgan, Inc., P.O. Box 1308, Jackson, NJ 08527
• Wildwood Herbal, P.O. Box 746, Albemarle, NC 28002
• Willhite Seed Company, Box 23, Poolville, TX 76076

• Ananthakrishnan, T. N. 1998.Technology in biological control. Enfield, NH: Science Pubs.
• Barboso, P. 1998.Conservation biological control. San Diego, CA: Academic Press.
• Boyland and Kuykendall, eds. 1998.Plant-microbe interactions and biological control.
  New York: Dekker, Marcel Press, Inc.
• Carson, R. 1999.Silent spring. Boston: Houghton Mifflin Co.
• Cook, R. J., and K. F. Baker. 1983.Nature and practice of biological control of plant pathogens.
  St. Paul, MN: American Phytopathological Society.
• Goeden, R. D., L. A. Andres, T. E. Freeman, P. Harris, R. L. Henry. 1981. Natural and applied control of insects by protozoa.Annual Review of Entomology26:49-73.
• Hawkins, B. A., and H. V. Cornell, eds. 1999.Theoretical approaches to biological control.
  New York: Cambridge University Press.
• Hoy, M., and G.L. Cunningham. 1983.Biological control of pests by mites: Proceedings of a conference.
  Oakland, CA: Agricultural and Natural Resources, University of California.
• Huffaker, C. B., and A. P. Gutierrez, eds. 1998.Ecological entomology, 2d ed.
  New York: Wiley& Sons.
• Jutsum, A. R., and R. F. S. Gordon, eds. 1989.Insect pheromones in plant protection.
  New York: John Wiley and Sons, Inc.
• Pickett, C. H. 1998.Enhancing biological control: Habitat management to promote natural enemies of agricultural pests.
  Berkeley, CA: University of California Press.
• Rechcigl, J. E. 1999.Biological and biotechnological control of insect pests. Los Angeles, CA: Lewis Publishing.
• Rice, E. L. 1984.Allelopathy,2d ed. San Diego, CA: Academic Press, Inc.
• Rice, E. L. 1995.Biological control of weeds and plant diseases: Advances in applied allelopathy.
  Norman, OK: University of Oklahoma Press.