| Pesticides Essay, Research Paper
Pesticides
Some 10,000 species of the more than 1 million species of insects are crop-eating, and of these, approximately 700 species worldwide cause most of the insect damage to crops, in the field and in storage. Humans have been on earth for more than 3 million years, while insects have existed for at least 250 million years. The first materials likely used by our primitive ancestors to reduce insect annoyance were mud and dust spread over their skin to repel biting and tickling insects, a practice resembling the habits of elephants, swine, and water buffalo. Under these circumstances, mud and dust would be classed as repellents, a category of insecticides.Historians have traced the use of pesticides to the time of Homer around 1000 B.C., but the earliest records of insecticides pertain to the burning of sulfur as a fumigant. Pliny the Elder (A.D. 23-79) recorded most of the earlier insecticide uses in his Natural History. Included among these were the use of gall from a green lizard to protect apples from worms and rot. Later, we find a variety of materials used with questionable results: extracts of pepper and tobacco, soapy water, whitewash, vinegar, turpentine, fish oil, brine, lye and many others.(Ware) There are specific control techniques that include chemical, physical, and biological mechanisms. Pests destroy about thirty-five percent of all crops worldwide. Even after harvesting the food, insects, microorganisms, rodents, and birds destroy another ten to twenty percent of the crops. Overall pests destroy forty to fifty percent of all crops. This causes may food shortages, so researchers are trying to find the best pest control to reduce food loss.
Pesticides contain herbicides(for weed control), insecticides, and fungicides. Over half of the pesticides used in the United States are herbicides that control weeds, and a small percentage of land in the UNited States are treated with pesticides. There is twenty-four percent, nine percent with insecticides, and one percent fingicides. The amount of pesticides that agriculturists use depend on what they are growing. Agriculturers in the United States, sixty-sven percent of them to be exact, use pesticicdes are applied to two crops, cotton and corn. about seventy percent of herbicides are applied to corn and soybeans, and most of the fungicides are applied to fruit and vegetable crops.
Some pesticides contain resmethrin, like Crossfire, Derringer, Raid, and Sun-Bugger(other brands use this too). Resmethrin is slightly toxic to practically non-toxic compound in EPA toxicity class III. The prodicts that contain resmithrin must have a word of caution on the label. This product is also letheal to fish. Resmithrin’s chemical class is pyrethroid and is used for control of flying and crawling insects, and mosiquito control. It’s also used for fabric control, pet sprays, and shampoo. It’s also applied to horses or horse stables. Resmithrin contains two main isomers; 20 to 30 percent of cis-isomer and 70 to 80 percent of trans-isomer.
Another popular pesticide is diaziron. Many brands like Basudin, Dazzel, and garden-tox use this. This too is a restricted pesticide, and only certified pest control operators can use it. In 1988, EPA canceled regristration od diazinon for use on golf courses and sod farms because many birds were dying. It is classified as toxicity class II- moderatley toxic. Products with diazinon must have WARNING or CAUTION labled somewhere on the bottle. Diazon’s chemical class is organophosphate. It’s used to control cockroaches, silverfish, ants, and fleas in residential, non food buildings. It’s also used on rice, fruit trees, sugar cone, tobacco, corn, and on norticultural plants. Its alos an ingredient in pest strips. Diazinon has a vettrenary use for fleas and ticks, and is available on granules, dust, wettable powder, seed dressings, and emulsifable solution formulations.
Many brands like Celthion, Cythion, Dielathion, and Emmaton use an ingredient called malathion. It is slightly toxic, therefore, making it class III, according to the EPA. This product must also say CAUTION or WARNING on it. Malathion is a general use pesticide and is available in emulsifable concentrate, wettable powder, dustable powder, and low form liquid forms. Like diazinon, its chemical class is organophosphate and is a widely used insecticide. It was one of the first organophosphate insecticides developed in 1950.The organochlorines are insecticides that contain carbon , hydrogen, and chlorine. They are also known by other names: chlorinated hydrocarbons, chlorinated organics, chlorinated insecticides, and chlorinated synthetics. Malathion is used for the control of mosquitoes, flies, house insects, anamil parasites like fleas and ticks, and head and body lice. It might also be found in formulations with many other pesticides.
Hexchlorocyclohexane (HCH)–the insecticidal properties of HCH were discovered in 1940 by French and British entomologists. In its technical grade, there are five isomers, alpha, beta, gamma, delta and epsilon. Surprisingly, only the gamma isomer has insecticidal properties. Consequently, the gamma isomer was isolated in manufacture and sold as the odorless insecticide lindane. In contrast, technical grade HCH has a strong musty odor and flavor, which can be imparted to treated crops and animal products. Because of its very low cost, HCH is still used in many developing countries.
Cyclodienes–The cyclodienes appeared after World War II: aldrin and dieldrin, 1948; heptachlor, endrin, mirex, endosulfan, and chlordecone. There were other cyclodienes of minor importance developed in the U.S. and Germany. Most of the cyclodienes are persistent insecticides and are stable in soil and relatively stable to the ultraviolet of sunlight. As a result, they were used in greatest quantity as soil insecticides for the control of termites and soil-borne insects whose larval stages feed on the roots of plants.
Polychloroterpenes–Only two polychloroterpenes were developed– Toxaphene had by far the greatest use of any single insecticide in agriculture, while strobane was relatively insignificant. Toxaphene was used on cotton, first in combination with DDT, for alone it had minimal insecticidal qualities. Then, after several major cotton insects became resistant to DDT, toxaphene was formulated with methyl parathion, an organophosphate insecticide mentiond later.
ORGANOPHOSPHATES
Organophosphates is the currently used generic term that includes all insecticides containing phosphorus. All organophosphates are derived from one of the phosphorus acids, and as a class are generally the most toxic of all pesticides to vertebrates. Because of the similarity of OP chemical structures to the “nerve gases”, their modes of action are also similar. Their insecticidal qualities were observed in Germany during World War II in the study of the extremely toxic OP nerve gases sarin, soman, and tabun. Initially, the discovery was made in search of substitutes for nicotine, which was heavily used as an insecticide but in short supply in Germany.
ORGANOSULFURS
These few materials have very low toxicity to insects and are used only as acaricides (miticides). They contain two phenyl rings, resembling DDT, with sulfur in place of carbon as the central atom. These include tetradifon propargite, comite, and ovex.
CARBAMATES
The carbamate insecticides are derivatives of carbamic acid. Like the OPs, their mode of action is that of inhibiting the vital enzyme cholinesterase.
The first successful carbamate insecticide, carbaryl, was introduced in 1956. More of it has been used worldwide than all the remaining carbamates combined. Two distinct qualities have made it the most popular carbamate: its very low mammalian oral and dermal toxicity and an exceptionally broad spectrum of insect control. Other carbamates are methomyl, carbofuran ,aldicarb, oxamyl, thiodicarb, methiocarb, propoxur, bendiocarb, carbosulfan, aldoxycarb, promecarb, and fenoxycarb.
FORMAMIDINES
The formamidines comprise a small group of insecticides. Three examples are chlordimeform, which is no longer registered in the U.S., formetanate, and amitraz. Their current value lies in the control of OP- and carbamate-resistant pests.
ORGANOTINS
The organotins are a group of acaricides that double as fungicides. Of particular interest is cyhexatin, one of the most selective acaricides known. Fenbutatin-oxide has been used extensively against mites on deciduous fruits, citrus, greenhouse crops, and ornamentals.
PYRETHROIDS
Natural pyrethrum has seldom been used for agricultural purposes because of its cost and instability in sunlight. Over the past two decades many synthetic pyrethrin-like materials have become available. They were originally referred to as synthetic pyrethroids. Currently, the better nomenclature is simply pyrethroids.
The pyrethroids have been evolutionized to better itself against insects, which is divided into four generations. The first generation contains only one pyrethroid, allethrin. Its synthesis was very complex, involving 22 chemical reactions to reach the final product.
The second generation includes tetramethrin, followed by resmethrin in 1967, then bioresmethrin, and finally phonothrin.
The third generation includes fenvalerate, and permethrin. These became the first agricultural pyrethroids because of their exceptional insecticidal activity and their photostability. They were virtually unaffected by ultraviolet in sunlight, lasting 4-7 days as efficacious residues on crop foliage.
The fourth and current generation, is the best because of their effectiveness.. These include bifenthrin, lambda-cyhalothrin, cypermethrin, deltamethrin, esfenvalerate, fenpropathrin, flucythrinate, fluvalinate, prallethrin, tau-fluvalinate, tefluthrin, tralomethrin, and zeta-cypermethrin. All of these are photostable, that is, they do not undergo photolysis in sunlight. And because they have minimal volatility they provide extended residual effectiveness, up to 10 days under optimum conditions.
Recent additions to the fourth generation pyrethroids are acrinathrin, and the still experimental imiprothrin.
NICOTINOIDS
The nicotinoids are a new class of insecticides with a new mode of action. They have been previously referred to as nitro-quanidines, neonicotinyls, neonicotinoids, chloronicotines, and more recently as the chloronicotinyls. Just as the synthetic pyrethroids are similar to and modeled after the natural pyrethrins, so too, are the nicotinoids similar to and modeled after the natural nicotine . Imidacloprid was introduced in Europe and Japan in 1990 and first registered in the U.S. in 1992.
Imidacloprid is a systemic insecticide, having good root-systemic characteristics and good contact and stomach action. It is used as a soil, seed or foliar treatment in cotton, rice cereals, peanuts, potatoes, vegetables, pome fruits, pecans and turf, for the control of sucking insects, soil insects, whiteflies, termites, turf insects and the Colorado potato beetle, with long residual control. Imidacloprid has no effect on mites or nematodes.
FIPROLES (or Phenylpyrazoles)
Fipronil is the only insecticide in this new class, introduced in 1990 and registered in the U.S. in 1996. It is a systemic material with contact and stomach activity. Fipronil is used for the control of many soil and foliar insects, on a variety of crops, primarily corn, turf, and for public health insect control. It is also used for seed treatment and formulated as baits for cockroaches, ants and termites. Fipronil is effective against insects resistant or tolerant to pyrethroid, organophosphate and carbamate insecticides.
PYRROLES
Chlorfenapyr is the first and only member of this unique chemical group, as both a contact and stomach insecticide-miticide. It is used on cotton and experimentally on corn, soybeans, vegetables, tree and vine crops, and ornamentals to control whitefly, thrips, caterpillars, mites, leafminers, aphids, and Colorado potato beetle. It has ovicidal activity on some species.
PYRAZOLES
The pyrazoles consist of tebufenpyrad and fenpyroximate. These were designed primarily as non-systemic contact and stomach miticides, but do have limited effectiveness on psylla, aphids, whitefly, and thrips. Tebufenpyrad is used experimentally on cotton, soybeans, vegetables, pome fruits, grapes and citrus. Fenpyroximate controls all stages of mites, gives fast knockdown, inhibits molting of immature stages of mites, and has long residual activity.
PYRIDAZINONES
Pyridaben is the only member of this class. It is a selective contact insecticide and miticide, also effective against thrips, aphids, whiteflies and leafhopprs. Registrations are for pome fruits, almonds, citrus, ornamentals and greenhouse ornamentals. Pyridaben provides exceptionally long residual control.
QUINAZOLINES
The quinazolines offer a unique chemical configuration, consisting only of one insecticide, fenazaquin. Fenazaquin is a contact and stomach miticide. It has ovicidal activity, gives rapid knockdown, and controls all stages of mites. It is used on cotton, stone and pome fruits, citrus, grapes and ornamentals.
BENZOYLUREAS
Benzoylureas are an entirely different class of insecticides that act as insect growth regulators (IGRs). Rather than being the typical poisons that attack the insect nervous system, they interfere with chitin synthesis and are taken up more by ingestion than by contact. Their greatest value is in the control of caterpillars and beetle larvae.
Benzoylureas were first used in Central America in 1985, to control a severe, resistant leafworm complex outbreak in cotton. The withdrawal of the ovicide chlordimeform made their control very difficult because of their high reistance to almost all insecticide classes, including the pyrethroids.
The first benzoylureas were introduced in 1978 by Bayer of Germany, triflumuron being the first. Others appearing since then are chlorfluazuron, followed by teflubenzuron, hexaflumuron, flufenoxuron, and flucycloxuron. Others are flurazuron, novaluron, and diafenthiuron. Lufenuron is the newest addition to this group, appearing in 1990. .
Most insecticieds now applied are long lasting synthetic compounds that affect the nervous system of insects on coontact. Most of the very affective products like chlorinated hydro carbons,DDT, chlordane, and toxaphane aree banned.DDT, colorless chemical pesticide, dichlorodiphenyltrichloroethane, used to eradicate disease-carrying and crop-eating insects. It was first isolated in Germany in 1874, but not until 1939 did the Swiss Nobel Prize-winning chemist Paul M ller recognize it as a potent nerve poison on insects. First used heavily in World War II for preinvasion spraying, DDT was disseminated in great quantities thereafter throughout the world to combat yellow fever, typhus, elephantiasis, and other insect-vectored diseases. In India, DDT reduced malaria from 75 million cases to fewer than 5 million cases in a decade. Crops and livestock sprayed with DDT sometimes as much as doubled their yields.
With the publication of the American marine biologist Rachel Carson’s Silent Spring in 1962, suspicion grew that DDT, by entering the food chain and eventually concentrating in higher animals, caused reproductive dysfunctions, such as thin eggshells in some birds. Some insect pests also gradually developed DDT-resistant strains whose populations grew unchecked while their natural predators, such as wasps, were being eradicated by spraying. In 1973 DDT was banned in the U.S. except for use in extreme health emergencies. Many other nations have also banned it or placed it under strict control.
Agricultural pesticides prevent a monettery loss of about one billion dollars each year in the United States alone. For every one dollar invested in pesticides, the average American farmer gets about four dollars in return. The costs include human poisonings, fish deaths, honeybee poisonings, and the contamination of livestock products. The United States have estimated at least one billion each year for the cost of pesticides.
Intergrated pest management is a recently developed technology for pest control that is aimed at acheiving the desired control while reducing the use of pesticides. To accomplish this, various combinations of chemical, biological, and physical controls are employed on the past , pesticides were all too often applied routinley weather, needed or not. IMP might reduce pesticide use by as much as fifty percent, while at the same time improving pest control. If this goal ia acheived, the environmental problems would be minimized, and significant benefits would result for farmers and society as a whole
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