As the plants develop, the insecticidal repellent effect 400 million years for a security system to protect them against insect attack has developed. The oldest known pest control method is human sacrifice, but since it is not effective, or maybe because of the lack of volunteers, plant dusts began being used and also plant extracts which are mentioned even in the Bible. Massive use of these insecticides has had a long and difficult road because the earliest data gathering done by researchers among farmers and natives revealed a lot of practices based on superstition, which, when tested by scientific methods were not shown to be effective. After the World War II the few plant and plant extracts that had shown promising effects, and were of widespread use, were replaced by synthetic insecticides. When synthetic insecticides appeared in the 1940’s some people thought that botanical insecticides would disappear forever but problems like environmental contamination, residues in food and feed and pest resistance brought them back to the fore. There is no doubt botanical insecticide is an interesting alternative to insect pest control, and on the other hand only a few of the more than 250,000 plant species on our planet have been properly evaluated for this purpose. This means the potential for the future may be huge. In fact, plants like neem, (Azadirachta indica A. Juss., Meliaceae), have shown excellent results and there already are commercial products in the market made from it. But one should not think success is at hand and botanical insecticides will replace all synthetic products. They are only alternatives that may be used in the Integrated Pest Management programs and they should be used together with other available control measures.
Use of plant extracts and powdered plant parts as insecticides goes back at least as far as the Roman Empire. For instance, there are reports that in 400 B.C. during Persian King Xerxes reign, the delousing procedure for children was with a powder obtained from the dry flowers of a plant known as pyrethrum (Tanacetum cinerariaefolium, Compositae). The first botanical insecticide, used as such, dates back to the XVII Century when it was shown that nicotine, obtained from tobacco leaves, would kill plum beetles. Around 1850 rotenone was introduced from the roots of plants called timbó. Up to that time this plant was used for fishing purposes only as natives hat known for a long time that throwing root pieces to the water caused fish to start floating a few minutes later, making them very easy to catch. Later on plants with irritating properties like incense are used: extracts from the later plant were used as decongestants. These plants did not kill insects directly but it was said that they scared them off. More recently other plants used are (Quaisa amara, Simaroubaceae), neem or margosa (A. indica) mentioned above, which besides giving excellent results for insect control are also a source of compounds used against cancer. Furthermore, the utilization of plant materials to protect field crops and stored commodities against insect attack has a long history. Many of the plant species concerned have also been used in traditional medicine by local communities and have been collected from the field or specifically cultivated for these purposes. Leaves, roots, twigs and flowers have been admixed as Protestants with various commodities in different parts of the world, particularly in India, China and Africa. Plant derived materials and phytochemicals, which once formed the basis of pest control technology, are again being scrutinized for potentially useful products or a s models for new classes of insecticides.
Amongst the most promising of the natural products investigated to date are the metabolites. Although only anout 10,000 secondary plant metabolites have been chemically identified, the total number of plant chemical may exceed 4,00,000. They are a vast commucopia of defense chemicals, comprising repellents, feeding and oviposition detterents, growth inhibitors, sterilants, toxicants, etc.
In Mexico and several Central American countries even today it is common practice to treat pests with plants known for their insecticidal properties as far back as the era of the Aztecs and Mayans. A case is this point is the use of a mixture of corns and beans with chili peppers (Capsicum frutescens; Solanaceae), rue (Ruta graveolens; Rutaceae) or garlic (Allium cepa; Alliaceae) still prevalent in these days.
At the present time there are a number of botanical insecticides being marketed, which are extracted from neem, grapefruit seeds and garlic, among other plants. Besides there are the synthetic copies of natural active ingredients like neonicotinoids where imidacloprid stands out. Lastly, it is worth mentioning that this is a field where new discoveries are made every day. However, the earth is inhibited by about one million insect species. Roughly a half of them feed on plants (Schoonhaven, 1983). Only plant species, which during millions of years have developed strong chemical defense system have survived the heavy selection pressure by greedy early created animals. Although, each of the defense systems having own intrinsic merit, some of them have featured which render them more generally applicable and from a technical point of view, easier to handle than others. It seems that modern science has discovered one of these rare opportunities to the pest.
Plants are like natural laboratories where a great number of chemicals are biosynthesized and in fact they may be considered the most important source of chemical compounds there are. Primary plant metabolism synthesizes essential compounds, which are present in all plant species. On the other hand, the end products of secondary metabolism are neither essential nor universally present in all plants. Common among these metabolites compounds with protective action against insects, such as alkaloids, not-proteic amino acids, steroids, phenols, flavonoids, glycosids, glucosinolates, quinines, tannins and terpenoids. Until now only a small part of the plant kingdom (estimated at 2,50,000 – 5,00,000 species around the globe) has been investigated phytochemically and the fraction subjected to biological and pharmacological screening is even lower. Since plants may contain hundreds or even thousands of metabolites, there is currently a resurgence of interest in the vegetable kingdom as a possible source of new lead compounds for introduction int the therapeutical screening programs (Hostettmann et al., 1995). The requirements for the prevention of damage and loss by infestation in stored products are simple. The products must be pest-free and admitted to store which they themselves can be maintained free from infestation. These requirements can at a price, be fulfilled and must be the aim in all food storage, providing the ratio of cost of treatment of value of good is economic without doubt, refrigeration cones nearest to perishable and valuable commodities (Hossain, 1990). Preventive measures are designed to keep the pest population below the injury level so that infestation cannot be developed in the stored products. This requires continuous program of work on the persons concerned (Hossain, 1990). Remedial measures are usually applied at a time when the infestation has become quite serious and some damage has already been done. The application of remedial measures also requires considerable preparation and involved expensive insecticides.
The suitability of a plant as food for insects depends on its chemical composition. In many cases, feeding inhibition is of primary importance in determining which plants are eaten and the extent to which they can be consumed (Thorsteinson, 1960; Hsiao, 1969). Antifeedants are significant importance in insect pest management because they are pest specific, non-poisonous and hence harmless to pest’s natural enemies. Antifeedants, which retard feeding activities of pest insect and reduce their damage by rendering treated plants unattractive, offer considerable scope in crop-protection (Munakata, 1970). These materials could be applied to crop plants in much the same way as insecticide.
Use of pesticides is often considered to be the most potent control technology for pests. But continuous or heavy use of some pesticides has created serious problems arising from factors such as, direct toxicity to parasites, predators, pollinators, fish and man (Munakata, 1977; Pimental, 1981), pesticide resistance (Brown, 1968; Georghiou andTaylor, 1977; Schmutterer, 1981; Waise et al., 1981) susceptibility of crop plants to insect pests (Pimental, 1977), and increased environmental and social costs (Pimental et al., 1980). Resistance to one or more pesticides has been reported in at least 477 species of insects and mites (Georghiou and Mellon, 1983), cross and multiresistant strains in many important insect species have also been reported (Dyte, 1970; Pasalu and Bhatia, 1983; Dyte and Halliday, 1985; Irshad and Gillani, 1990; Zettler and Cuperus, 1990; Zettler, 199)
The increasing serious problems of pest resistance to pesticides and of contamination of the biosphere associated with the large scale use of broad spectrum synthetic pesticides have dictated the need for effective biodegradable less hazardous safe pesticides with greater selectivity (Saxena, 1983). The awareness has created a worldwide interest in the re-evaluation and use of age-old, traditional botanical pest control agents (Heyde et al., 1983) Further synthetic insecticides are not only a threat to the farmers’ major resources but also used beyond the permissible limits (Lepigre and Pointel, 1971). Safe and inexpensive insecticides coupled with simple application methods are needed at the rural level (Periera and Wohlgemuth, 1982). In many areas of the world locally available materials are widely used to protect stored products (Golob and Webley, 1980).
Insecticides of plant origin are considered as alternatives to the synthetic chemicals from begin pest specific and biodegradable in nature (Periera and Wohlgemuth, 1982). So, derivatives of some plants have had temporary to restricted use in pest control or have been considered items of regional interest (Saxena et al., 1983). The chemistry and biological activity of these plants have recently been studied, but even after a long history of pest control potential, these plants have not been fully utilized for pest control. This paradox can be attributed to the earlier prediction to research workers for chemicals that will rather than those that subtly alter the pests’ behavior and physiology. Only recently the potential of behavioral and physiological aberrations may be highly desirable to minimize the risk of exposing the pests’ natural enemies to poisoned food or starvation.
Renewed interest in botanical pest control agents is motivated by three major objectives; to encourage traditional use of simple formulation of locally available plant materials by farmers who can not afford commercial insecticides; to identify sources of new botanical pesticides for commercial extraction; and to elucidate the chemical structure of active principles. Botanical pest control agents extracted on large scale may also be used to replace for supplement the activity of existing synthetic pesticides against refractory pests. Structural elucidation of the active constituents may provide further insight into structure-activity relationships. Novel metabolites identified may serve as models for chemical synthesis of new pesticides with more desirable properties (Saxena et al., 1983).
In this investigation D. metel Linn was selected of screening against T. castaneum for its insectidal potential.
Morphological attributes systemic position and distribution of the plant species
D. metel Linn. is a native plant of tropical Asia, now pantropic in distribution. It is found in open waste lands all over the country. This plant is a hybrid between D. fastuosa Linn. and D. alba Nees. D. metel is known as “mad egg plant” in some places of our country.
Datura are herbaceous, leafy annuals and short-lived perennials which can reach up to 2 meters in height. The leaves are alternate, 10-20cm long and 5-18cm broad, with a lobed or toothed margin. The flowers are erect or spreading (not pendulous like those of the closely allied Brugmansia), trumpet-shaped, 5-20 cm long and 4-12cm broad at the mouth, colors vary from white to yellow, pink and pale purple. The fruit is a spiny capsule 4-10cm long and 2-6cm broad, splitting open when ripe to release the numerous seeds. The seeds disperse freely over pastures, fields and even wasteland locations. Datura belongs to the classic witches weeds along with deadly nightshade, henbane, and mandrake. Most parts of the plants contain toxic hallucinogens, and Datura has a long history of use for causing delirious states and death. It was well known as an essential ingredient of love potions and witches brew.
Species: Datura metel
Background information on the test organisms
The rust-red flour beetle, T. castaneum (Herbst) is one of the most serious products. It is commonly known as ‘red flour beetle’ (Coleoptera: Tenebrionidae). Mouth-parts of this pest insect are not adapted to feed on hard whole grains and they are thus found in almost any kind of flour, cracked grains etc. (Chittenden, 1897) listed the specific food of T. castaneum, which includes whole-wheat flour, bran, rice flour, cornmeal, barley flour and oatmeal. It also feeds upon dried fruits, dried plant roots, nuts chocolates, drugs, snuff, cayenne pepper, pulses and prepared cereal foods such as corn flakes (Metcalf and Flint, 1950).
They are found in great numbers on infested materials and caused serious losses and considerable damage to flour and grains that have previously been attacked by other pests. Much of the damage done by T. castaneum is directly to kernels (germ and endoplasm). In case of severe infestation flour or other materials invaded may have a characteristics pungent odor as a result of the gaseous secretion exuded by the beetle. Such flour has an exceedingly low viscosity and its elasticity is markedly affected, which may cause gastric disturbance if used as food (Payne, 1925). In severe infestation, the flour turn grayish and moldy and has a pungent, disagreeable odor making it unfit for human consumption (Good, 1936). Infested material will show many elongate reddish brown beetles, about 1/7 inch ling crawling over the material when it is disturbed and brownish white (somewhat flattened) six-larval larval bedding on the inside of the grain kernels and crawling over the infested seeds. They are generally known among millers as bran bugs. T. castaneum contaminates more than they consume.
Both the larva and adults cause damage. The young larva is yellowish white and measures 1 mm in length. As it matures, it turns reddish yellow, becomes hairy and measures over 6 mm in length. Its head, appendages and the last abdominal segment are darker. The adult is a small reddish-brown beetle, measuring about 3.5 mm in length and 1.2 mm in width. Its antennae are bent and bear a distinct club formed by the three enlarged terminal joints. The last antennal segment is transversely rounded. The exact origin of T. castaneum is not known but according the Blair (1930) it was commonly found in the wild state in rotting wood and in loose bark of trees in India.
Tribolium species are major pests of stored grains and grain products in the tropics (Howse, 1965) Control of these insects relies heavily on the use of synthetic insecticides and fumigants, which has led to problems such as disturbances of the environment, increasing costs of application, pest resurgence, pest resurgence, pest resistance to pesticides and lethal effects on non-target organisms in addition in addition to direct toxicity to users (Jembere et al., 1995; Okonkwn and Okoye, 1996).
Aim and objective of this work
D. metel is one kind of plants that has been studied a lot phytochemically and only a few studies have been done only with its medicinal properties, but in details a very few works have done till to date on its use for the control of crop pests. Accordingly, a research topic entitled “Insecticidal activity of Datura metel Linn. against the red flour beetle, Tribolium castaneum (Hbst.) adults” was taken into consideration.
- To trace presence of pest control potentials (pesticidal) in the target plant, D. metel.
- . To evaluate efficacy of the promising extracts against the stored grain pest, T. castaneum by establishing LD50 values through surface film assay.