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Biological Control: An Ecological Approach to IPM


Biological Control: An Ecological Approach To Pest Management For Farms, Ranches, & Gardens

by: Everett Dietrick, about 1990


Biological control is nature's way of regulating insect pest populations. Damage due to plant-feeding insects and mites can best be prevented when sufficient predatory and parasitic organisms keep the pests reduced to tolerable or "economic" levels (that level below which the pest does no damage to the plant). These natural enemies have been regulating plant-feeding pests since ancient times. Today, more than ever, we need to exploit their usefulness in the family garden as well as on the modern farm.What is biological control?Insects have been controlled by other insects, and diseases of insects, since the beginning of time. For our purposes here, we define beneficial insects as those insects beneficial to man in his efforts to harvest nature; and we define pest insects as those insects which are harmful to plants and animals. Certain beneficial insects called predators feed on several different kinds of prey, and they require multiple prey individuals in order to complete their development to the adult stage. Parasites, on the other hand, usually complete their development on or inside a single host individual (a host is that insect on or in which the parasite feeds and grows). Predators and parasites do not become pests themselves, since these beneficial insects are programmed by nature to adjust their own populations to fit those of the pests. This is all part of the balance of nature which regulates pest populations all over the world. In the natural scheme of things, each insect species has its own population range set up by mother nature. If one species should increase its numbers above that range, the insects which prey on that particular species (or parasitize it) will increase their own populations accordingly, since there is so much more food available. The carnivorous beneficial insects devour the pests, thus increasing their own populations at the expense of the pest populations. When the pest population has been brought down to its normal range in nature, the reduced amount of food will cause the predatory and parasitic populations to be reduced again (through starvation or lack of hosts); thus, nature is brought back into a satisfactory balance.


Augmentation of this natural control, or the balance of nature, is also called biological control. Biological control is merely another name for aiding the balance of nature, by adding beneficial insects to the fields to help control the pest insects. Entomologists at Rincon–Vitova Insectaries have developed pest management programs that exploit this natural control through habitat management (farming & gardening practices) and colonizations of beneficial predators and parasites. Our programs are designed to help biological control of pests on farms, ranches, and gardens.Pests are only pests when they occur in intolerable numbers!


Biological control does not mean eradication of the pest populations. It is, rather, a balance of insects, both good and bad, that keeps the pests from expanding to dangerous levels. This concept is essential to the understanding and implementation of successful biological control. It is only the intolerable numbers of surplus pest individuals causing intolerable damage to plants that are truly pests. The balance between good bugs and bad bugs is never static, but changes constantly, and is never equally distributed; some areas or branches are more heavily infested with pests than certain others; on the other hand, in certain areas of the garden there are reservoirs of beneficial predators and parasites in greater concentration. Pests will concentrate in spots or on branches that protrude, etc.; they may concentrate in a spot where some factor has previously eliminated biological control (ants protecting aphids, road dust interfering with predation, pesticide residues killing beneficial insects, winds carrying in pests from neighboring fields, etc.). Little pest fires like this can rapidly turn into holocausts, wiping out an entire garden, unless there is a complex of beneficial insects present to suppress them. The aim of biological control, therefore, is to create the best possible overall balance of beneficial insects in the garden, so that these little pest flareups can be quickly put out before they start to spread. Successful biological control can be achieved when there is a wide variety of all kinds of insects in the garden, both good and bad ones.


Low populations of some of the less destructive pest insects are necessary in a garden, for they serve as food to keep the beneficial insects healthy and in the garden. Another great source of food for the beneficial insects are the pollenators and other incidental species which are attracted to decomposing organic wastes (leaves, prunings, animal manures, etc.). If there were no pest or decomposing insects to feed on, the beneficial insects would either die off or leave the garden in search of food. Again, the idea here is one of a balance of insects. When this balance is established in the garden, the insects will then take over the job os regulating their own populations.Good cultural practices are essential to biological control.


This overall balance in the garden can best be established with the creation of a suitable habitat for the insects in the garden, both the pests and the beneficial insects. One of the most interesting aspects of biological control is the beneficial insect habit of being attracted to a suitable physical habitat, and then turning to attack their hosts present in that habitat. The insects, therefore, need a habitat in which they can thrive, or many of them will die off or leave the garden. Implementation of good cultural practices to create a good habitat is essential to a successful biological control program.The key to creating a good habitat for the insects is establishing a diversity of nature in the garden. Nature is based on diversity, and it is a complex of interacting factors which favors successful biological control. It is very rare that a single beneficial insect species ever gives complete control of a certain pest; rather, it is the interaction of several different predator and parasite species that gives effective overall pest regulation. For example, if one set of predators and parasites can destroy a certain percentage of pest eggs, another set will more easily be able to reduce the remaining population of adults on which they feed. Thus, the idea is to attract and retain as many kinds of beneficial insects as possible in the garden, as a general buffer against pests. This can best be accomplished through a diversity of plants. Different kinds of plants attract different kinds of insects, resulting in a biological balance in the garden. Plant as wide a variety of plants as possible, and plant them in small blocks. Plant flowering plants as well as vegetables and fruit trees; they will not only make the garden more beautiful, but will also help create a biological balance by providing pollen and nectar for the beneficial insects. Strong, healthy plants can outgrow many potentially serious pest situations; humus-forming mulch can help control weeds and provide additional plant food, while helping retain moisture in the ground. Limited numbers of natural grasses and even weeds can provide a protective niche for predators and parasites, providing host insects, nectar, pollen, and sources of water in dews and moist organic litter on the soil surface. Beneficial insects are small, with a high surface-to-volume ratio, and they lose their water content quickly in unfavorable environments. In order to survive, they must be able to replenish their water content. In general, most insects need a drink of water each day; if water is not provided in the habitat, predators may turn to the plants as a source of moisture, and thus become minor pests themselves. It is very important, therefore, that we provide free water in the garden for the beneficial insects.In addition to diversifying plantings, try to keep a sequence of plants planted in the garden at all times, even if this means planting green manures or sod grasses for the compost heap. Crop rotation can be accomplished in the garden just as it is on the farm, only on a smaller scale, especially if the plantings are in permanent beds with permanent walk areas. This sequence of plantings (which is just a matter of planting whatever can be grown in each season throughout the year) will retain the complex of insects in the garden. When the garden is abandoned during the winter, the insects will overwinter in the plant refuse. Surplus plant residues, litter, and other garden waste products should be rapidly composted to remove them as potential habitats for the pests. This composting helps provide the decomposing organisms which are a valuable alternate food source for the beneficial insects. A constantly active garden will retain a constantly active complex of insects, ready at all times to help control garden pests.All in all, the more diversity the better. The more plants in a garden, the more kinds of insects will reside there. The more kinds of insects in a garden, the better the biological balance will be. The many varieties of insects will help control each other; and the beneficial ins will remain there even when pest populations are low, because there will be pollen, nectar, alternate hosts, and sources of water for the feed on until they are needed again to help suppress the pests. In this way, an overall balance is created in the garden, providing a su habitat for all insects, and helping to give better pest control. WARNING - Ant control is important! Ants protect aphids and other hoi producing pests from their natural enemies by destroying them and otherwise disturbing their control effects.Release of insectary-grown beneficial insects helps biological control.


Biological control can be augmented by colonizations of insectary-grown predators and parasites. The addition of even low numbers of beneficial insects can tip the balance of nature in favor of the good insects. The insectary can guarantee the presence of certain beneficial species through periodic releases, thus improving the ratio of good insects to pests. The battle of the bugs is won when there are sufficient predators and parasites present to destroy the majority of pests. Thus, the number of beneficial insects required depends completely on natural complex present in the garden and the extent of the pest problem. The more beneficial insects present in the garden, the better pest control will be. On many occasions, there is an insufficient number of natural enemies present for effective pest control. Therefor releases of these insects into the garden will augment the populations already there, and give more effective pest control by helping to establish a better balance of insects in the garden. In order to cover all potential pest situations, it is advisable to make a series of re of beneficial insects, rather than just a single large release.


What does Rincon-Vitova, Inc. offer for biological control?Trichogramma wasps: these very tiny wasps, which are harmless to people, attack all kinds of moth and butterfly eggs. They lay their eggs in the eggs of the moth or butterfly. The immature Trichogramma devour the moth egg and hatch into parasites; in this way, more Trichogramma parasites are grown each generation. It is important to start colonizations as soon as there are any host eggs present. Black-light insect traps are good indicators for the presence of egg-laying moths. Trichogramma develop more quickly in summer than in winter. A generation takes 10 days at 80 degrees. Maximum kill of pest eggs can prevent worms from hatching. It is advisable to colonize this egg killer frequently to prevent as many worms as possible from hatching. Trichogramma recommendations are as follows:Vegetable and Flower Gardens -For a moderate sized garden, 15,000 Trichogramma is usually sufficient for each release. Make three releases two weeks apart, preferably starting when the garden is growing well in the spring. Additional releases should be made when pest problems are severe.Deciduous Fruit and Nut Orchards -Release 15,000 to the acre as soon as the leaves are fully emerged and repeat this colonization for five weeks. This will cover the spring flights of most moths that enter the orchards. Some varieties of fruit have more severe pest situations and therefore larger numbers released will give better results. We cannot recommend an exact number because of the difference in size of trees and the degree of infestation. However, we do know that Trichogramma work if good judgment is used. Ornamentals, Citrus, Avocados–The above recommendations hold for non–deciduous trees and bushes except that the timing of the releases should begin in early summer when moth activity speeds up. Try to match your releases to the flights of the moths and butterflies that lay the eggs.Alfalfa, Cotton, Sorghum, Field Corn, Grains -All are infested by various worm pests. Weekly releases of 2,000 to 5,000 Trichogramma per acre starting with the first warm weather in early summer have been found to help biological control.Green lacewings );Chrysopa carnea) these small, pale green insects have gained national attention as all–purpose predators of insects and mites. Lacewings are an effective natural enemy of aphids, mites, whiteflies, mealybugs, leafhoppers, thrips, all sorts of moth and butterfly eggs, and caterpillars. The larva is known as the "aphid lion" because of its voracious appetite for aphids. Just as Trichogramma is the universal egg parasite, lacewings are the "broad-spectrum" predators that are useful in biological control of nearly every crop and pest situation. It is common sense to augment this beneficial predator wherever and whenever possible in all pest situations in all crops.The ladybugs (Hippodamia convergens) that are field collected in the hibernation sites and sold by other insectaries, fly away from the yard where they are needed more often than not.


Rincon–Vitova has developed a program of conditioning the diapausing ladybugs so as to wake their reproductive activity. Rincon–Vitova ladybugs are pre-fed and conditioned so they are ready to feed and lay eggs in the garden when they encounter aphids. It is important to point out that ladybugs are dependent upon aphids to trigger their egg-laying response, whereas lacewings are released as hatching eggs that will eat any pest they encounter. Lacewings go right to work on the widest spectrum of pests without conditioning.


Our recommendations for using lacewings are: minimum order of approximately 3 to 5 thousand for a small garden. These tiny larvae should be released in as many pest situations as possible so as to "seed" these important predators into the garden early in the spring. Best timing is with the first aphids of the year. However, lacewings may be released successfully at any time of the year. Augmentation releases made in all pest situations as they develop gives maximum biological control. Lacewings control orchard pests equally as well. Eggs and larvae can be placed where tree branches touch the ground or in the crotch of the tree, or by being salted onto leaves. Larvae are extremely secretive and hold on to plant surfaces.


Fly parasites: these tiny parasitic wasps are released for fly control in breeding sites on poultry and egg farms, dairy and beef cattle feed lots, and backyard horse stalls and other domestic animal manure accumulations. The parasites attack flies by laying their eggs in the larvae and pupae. The eggs hatch inside the flies, and the parasites eat the immature flies, then emerge as adult parasites. They cannot become pests themselves, since they can only survive by finding other immature flies on which to lay their eggs.Costs of these biological control insects varies according to the severity of the problem; there is no set amount to purchase in order to achieve control. See our accompanying brochures for some suggestions on amounts needed. In addition to the insects listed above, Rincon–Vitova Insectaries also market several other kinds of beneficial insects for use in controlling farm, ranch, and garden pests.


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