The Ayurveda system attributes the cure of an ailment to the entire plant or its crude extract containing multiple chemicals, while the allopathy system attempts to extract the particular chemical from the plant or other organisms, purifies and prepares it as a tablet or capsule. According to the latter system, there is one chemical for one cure and emphasis is laid on purity of the chemical, while the former aims at utilising all possible chemicals.
A similar dichotomy prevails in the use of pesticides in agriculture. Farmers have traditionally used crude extracts from plants as pesticides, while the modern pesticide industry emphasises the use of the particular chemical responsible for the action. The stress is on purifying and concentrating the chemical in commercial formulations. Which is a better option? The crude extract or the purified chemical?
This has been a subject of debate for a long time in both medicine and agriculture.
A recent publication in the journal, Current Science (June 2003), by a team of scientists namely A R V Kumar, K Chandrashekara, H C Jayadevi and H J Ashoka at the Department of Ento-mology, University of Agricultural Sciences addresses this issue using neem and its most active insecticidal chemical azadir-achtin as the model system.
Neem (Azadirachta indica) is widely recommended for use in agriculture as an alternative to synthetic insecticides. It leads the list of plants with the highest potential to control pests largely because it contains a variety of biologically active compounds. These compounds together called limonoids, are present in various parts of the plant including the leaf, bark and seeds. However the seeds contain the highest quantities.
Crude water extract of neem seed kernels has been widely used traditionally for pest management in crops as in Ayurveda and is shown to be a highly potent pesticide. The crude extracts are known to contain more than 100 chemicals of which many are biologically active against insects. Neem has multiple modes of action against insects including repellence, feeding deterrence, growth disruption, reduced fecundity, mating disruption, etc. Much of this activity is however, attributed to azadirachtin, the most abundant limonoid in neem.
Employing modern chemical technology, like in Allopathy, extracts of azadirachtin (which is found in high concentrations in the seed) have been extensively used in commercial neem formulations (CNFs). In the last decade farmers have had access to several azadirachtin based formulations available in the market in the form of liquids or water-soluble powders. Earlier, products with azadirachtin concentrations of 300 and 1,500 parts per million (ppm) were available. Of late, CNFs are available with concentrations as high as 65,000 ppm. On the face of it, formulations with higher azadirachtin content should fare better as a pesticide than formulations having lower content. But the UAS scientists have found some surprising results.
They carried out two separate studies to understand the effects of azadirachtin at varying concentrations on the diamond moth (Plutella xyloste-lla), which is a notorious pest on cabbage. The researchers chose eight brands of CNFs prepared using different formulation techniques and having a wide range of concentrations (from 300 to 50,000 ppm) of azadirachtin. Bioassay tests were carried out using the leaf dip method to understand the amount of azadirachtin required for obtaining 50 per cent kill of the insect for all the products under test. To their surprise, they found that the quantity of azadirachtin required for obtaining 50 per cent kill of the test insect increased with the concentration of the azadirachtin in the CNF. Repeated tests confirmed the results and clearly indicated a commensurate reduction in the biological efficiency of azadirachtin in products with higher concentration. Why is this so?
According to the researchers, neem has a bouquet of limonoids. Many of them are biologically as active as azadirachtin. Besides, many compounds related to azadirachtin might act as synergists in enhancing its biological activity. But during the process of concentration of azadirachtin in the development of commercial formulations, it is likely that other potent chemicals are lost. As a result, greater the concentration of azadirachtin, lower will be the diversity of other biologically active compounds leading to the loss of other potent chemicals and the possible synergists of azadirachtin. Eventually, this leads to decrease in effectiveness of the chemical at higher concentration thus making CNFs with higher azadirachtin content to be less biologically efficient than crude extracts.
These surprising results have made the investigators to intensify their efforts to get a better understanding of the process at work which determines the efficiency of azadirachtin based formulations vis-à-vis crude neem extracts. Other field studies by the team has also shown the superiority of home made crude aqueous extract of neem seed kernels (NSKE) in managing the caterpillar pests and thus the call for the farming community to make full use of the local neem resources.
Drawing parallels, the researchers also feel that the phenomenon could be much more widespread than being limited to neem and its formulations. Recent studies at the Bangalore based Foundation for Revitalisation of Local Health Traditions (FRLHT), on Brahmi plant and its extracts seem to agree with the findings of UAS team. Brahmi plant is known to contain Bacosides, the memory enhancing drugs.
Bacosides are now extracted, formulated into pills and marketed in India under various brand names. Preliminary studies carried out at FRLHT have indicated that the fresh leaves of Brahmi have more memory enhancing activity as compared to the extracts (Amita Kaushal in Amruth, September- October, 2003, Vol. 7, issue 5).
For more details, contact Department of Entomology, UAS, Bangalore.
A similar dichotomy prevails in the use of pesticides in agriculture. Farmers have traditionally used crude extracts from plants as pesticides, while the modern pesticide industry emphasises the use of the particular chemical responsible for the action. The stress is on purifying and concentrating the chemical in commercial formulations. Which is a better option? The crude extract or the purified chemical?
This has been a subject of debate for a long time in both medicine and agriculture.
A recent publication in the journal, Current Science (June 2003), by a team of scientists namely A R V Kumar, K Chandrashekara, H C Jayadevi and H J Ashoka at the Department of Ento-mology, University of Agricultural Sciences addresses this issue using neem and its most active insecticidal chemical azadir-achtin as the model system.
Neem (Azadirachta indica) is widely recommended for use in agriculture as an alternative to synthetic insecticides. It leads the list of plants with the highest potential to control pests largely because it contains a variety of biologically active compounds. These compounds together called limonoids, are present in various parts of the plant including the leaf, bark and seeds. However the seeds contain the highest quantities.
Crude water extract of neem seed kernels has been widely used traditionally for pest management in crops as in Ayurveda and is shown to be a highly potent pesticide. The crude extracts are known to contain more than 100 chemicals of which many are biologically active against insects. Neem has multiple modes of action against insects including repellence, feeding deterrence, growth disruption, reduced fecundity, mating disruption, etc. Much of this activity is however, attributed to azadirachtin, the most abundant limonoid in neem.
Employing modern chemical technology, like in Allopathy, extracts of azadirachtin (which is found in high concentrations in the seed) have been extensively used in commercial neem formulations (CNFs). In the last decade farmers have had access to several azadirachtin based formulations available in the market in the form of liquids or water-soluble powders. Earlier, products with azadirachtin concentrations of 300 and 1,500 parts per million (ppm) were available. Of late, CNFs are available with concentrations as high as 65,000 ppm. On the face of it, formulations with higher azadirachtin content should fare better as a pesticide than formulations having lower content. But the UAS scientists have found some surprising results.
They carried out two separate studies to understand the effects of azadirachtin at varying concentrations on the diamond moth (Plutella xyloste-lla), which is a notorious pest on cabbage. The researchers chose eight brands of CNFs prepared using different formulation techniques and having a wide range of concentrations (from 300 to 50,000 ppm) of azadirachtin. Bioassay tests were carried out using the leaf dip method to understand the amount of azadirachtin required for obtaining 50 per cent kill of the insect for all the products under test. To their surprise, they found that the quantity of azadirachtin required for obtaining 50 per cent kill of the test insect increased with the concentration of the azadirachtin in the CNF. Repeated tests confirmed the results and clearly indicated a commensurate reduction in the biological efficiency of azadirachtin in products with higher concentration. Why is this so?
According to the researchers, neem has a bouquet of limonoids. Many of them are biologically as active as azadirachtin. Besides, many compounds related to azadirachtin might act as synergists in enhancing its biological activity. But during the process of concentration of azadirachtin in the development of commercial formulations, it is likely that other potent chemicals are lost. As a result, greater the concentration of azadirachtin, lower will be the diversity of other biologically active compounds leading to the loss of other potent chemicals and the possible synergists of azadirachtin. Eventually, this leads to decrease in effectiveness of the chemical at higher concentration thus making CNFs with higher azadirachtin content to be less biologically efficient than crude extracts.
These surprising results have made the investigators to intensify their efforts to get a better understanding of the process at work which determines the efficiency of azadirachtin based formulations vis-à-vis crude neem extracts. Other field studies by the team has also shown the superiority of home made crude aqueous extract of neem seed kernels (NSKE) in managing the caterpillar pests and thus the call for the farming community to make full use of the local neem resources.
Drawing parallels, the researchers also feel that the phenomenon could be much more widespread than being limited to neem and its formulations. Recent studies at the Bangalore based Foundation for Revitalisation of Local Health Traditions (FRLHT), on Brahmi plant and its extracts seem to agree with the findings of UAS team. Brahmi plant is known to contain Bacosides, the memory enhancing drugs.
Bacosides are now extracted, formulated into pills and marketed in India under various brand names. Preliminary studies carried out at FRLHT have indicated that the fresh leaves of Brahmi have more memory enhancing activity as compared to the extracts (Amita Kaushal in Amruth, September- October, 2003, Vol. 7, issue 5).
For more details, contact Department of Entomology, UAS, Bangalore.
This n article appeared in Deccan Herald on 2nd December, 2003.
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