Biological control can be used against all types of pests, including vertebrates, plant pathogens, and weeds as well as insects, but the methods and agents used are different each type of pest. CBSE Class 12 Biology - Microbes in Human Welfare notes.pdf Author:Approaches to the Biological Control of Insect PestsConnecticut Agricultural Experiment StationTelephone: (203) 974-8458 Fax: (203) 974-8502E-mail: control is the use of living organisms to suppress pest populations, making them less damaging than they would otherwise be. Microbes as Biocontrol Agents : Insecticides and Pesticides toxic, harmful & are pollutants. The ‘New Association’ or ‘Neoclassical’ approach targets native pests with non-native biological control. ‘Classical’ biocontrol targets a non-native pest with one or more species of biocontrol agents from the pest’s native range 2. There are several general approaches to using biocontrol agents: 1.
The adults are typically free-living, and may be predators. Spiders and some families of mites are also predators of insects, pest species of mites, and other arthropods.Parasitoids: Parasitoids are insects with an immature stage that develops on or in a single insect host, and ultimately kills the host. Important insect predators include lady beetles, ground beetles, rove beetles, flower bugs and other predatory true bugs, lacewings, and hover flies. Insect and other arthropod predators are more often used in biological control because they feed on a smaller range of prey species, and because arthropod predators, with their shorter life cycles, may fluctuate in population density in response to changes in the density of their prey. These insectivorous vertebrates usually feed on many insect species, and rarely focus on pests unless they are very abundant.
This fungus is believed to have been introduced about 1911, but was not discovered in forests until 1989, when it was widespread and abundant in New England. Under certain environmental conditions, diseases can multiply and spread naturally through an insect population, particularly when the density of the insects is high.An example of an established population of an insect pathogen which has been successfully controlling its host is the fungus Entomophaga maimaiga, a pathogen of the gypsy moth. In addition, insects are also attacked by some species of nematodes that, with their bacterial symbionts, cause disease or death. These diseases may reduce the rate of feeding and growth of insect pests, slow or prevent their reproduction, or kill them. Thus, accurate identification of the host and parasitoid species is critically important in using parasitoids for biological control.Pathogens: Insects, like other animals and plants, are infected by bacteria, fungi, protozoans and viruses that cause disease. Because parasitoids must be adapted to the life cycle, physiology and defenses of their hosts, they are limited in their host range, and many are highly specialized.
Although there are variations by crop and class of pesticide, the overall trend is that previous reductions, due to the substitution of economic thresholds for calendar spraying and the use of pesticides effective at lower dosages, are being reversed by increases in acreage treated and number of treatments per season. Has been stable or increasing since the late 1980’s. Many IPM programs, however, have not been able to move beyond the first stage of developing sampling methods and economic thresholds for pesticide application.Several USDA and EPA surveys of pesticide use in major crops indicate that the quantity of pesticides used in the U.S. The need for pesticides can be reduced by use of resistant varieties, cultural methods that reduce pest abundance or damage, methods of manipulating pest mating or host-finding behavior, and, in some cases, physical methods of control. The original idea that inspired integrated pest management (IPM) was to combine biological and chemical control by reducing pesticide use to the minimum required for economic production, and applying the required pesticides in a manner that is least disruptive to biological control agents. Conservation of existing natural enemiesReducing pesticide use: Most natural enemies are highly susceptible to pesticides, and pesticide use is a major limitation to their effectiveness in the field.
In general, systemic insecticides, which require consuming plant material for exposure, and insecticides that must be ingested for toxicity affect natural enemies much less than pests.Pesticides may also have more subtle effects on the physiology of natural enemies than direct toxicity. Among the insecticides, synthetic pyrethroids are among the most toxic to beneficials, while Bacillus thuringiensis and insect growth regulators were among the least toxic. This database compares the toxicity of different pesticides and the "selectivity ratio" - the dose required to kill 50% of the target pest divided by the dose that kills 50% of the affected natural enemy species. A database has been compiled on the effects of pesticides on beneficial insects, spiders and mites (summarized in Croft 1990 and Benbrook 1996). While insecticides and acaricides are most likely to be toxic to insect and mite natural enemies, herbicides and fungicides are sometimes toxic as well. This strategy is sometimes called "biointensive IPM."Selecting and using pesticides to minimize the effect on natural enemiesThe effect of a pesticide on natural enemy populations depends on the physiological effect of the chemical and on how the pesticide is used - how and when it is applied, for example.
A classic example is the overwintering of predacious mites in fruit orchards. Some parasitoids and pathogens overwinter in the bodies of their hosts (which may then have overwintering requirements of their own), but others may pass the winter in crop residues, other vegetation, or in soil. The effectivenss of limiting the areas treated may depend on the mobility of the natural enemy and the pest.Providing habitat and resources for natural enemiesNatural enemies are generally not active during the winter in the Northeast, and thus, unless they are re-released each year, must have a suitable environment for overwintering. Spot applications in the areas of high pest density or treatment of alternating strips within a field may leave natural enemies in adjacent areas unaffected. Less persistent pesticides reduce contact, especially if used with knowledge of the biology of the natural enemy to avoid susceptible life stages. Certain herbicides (diquat and paraquat) make the treated soil in vineyards repellent to predacious mites.The impact of pesticides on natural enemies can be reduced by careful timing and placement of applications to minimize contact between the beneficial organism and the pesticide.
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