Agriculture has had to face the destructive activities of numerous pests like fungi, weeds and insects from time immemorial, leading to radical decreases in yields. With the advent of chemical pesticides, this crisis was resolved to a great extent. But the overdependence on chemical pesticides and eventual uninhibited use of them has caused serious health and environmental problems.
Green Alternatives - Biopesticides
Biopesticides or biological pesticides are derived from natural materials like animals, plants, bacteria, and certain minerals. For example, garlic, mint, neem, papaya and baking soda all have pesticidal applications and are considered biopesticides. According to the U. S. Environmental Protection Agency (USEPA), at the end of 1998, there were approximately 175 registered biopesticide active ingredients and 700 products. The most commonly used biopesticides are living organisms (bacteria, viruses and fungi) which are pathogenic for the pest of interest. These include biofungicides (Trichoderma), bioherbicides (Phytopthora) and bioinsecticides (Bacillus thuringiensis).
Advantages of Using Biopesticides
- Biopesticides are obviously less harmful than conventional chemical pesticides.
- Biopesticides generally target one specific pest or a small number of related pests in contrast to broad spectrum chemical pesticides which affect, apart from the pest, other beneficial insects, birds and mammals.
- Biopesticides are more effective in smaller quantities and decompose quickly and thus do not cause the kind of environmental problems associated with chemical pesticides.
- When used in Integrated Pest Management programs, biopesticides can greatly reduce the use of conventional pesticides, while the crop yield remains high.
Biofungicides using Trichoderma
Trichoderma is a fungus which is present in nearly all soils and other diverse habitats. They attack and parasitize other fungi. So far, Trichoderma has been successful in controlling every plant-pathogenic fungus against which it has been used. Preparation of Trichoderma biopesticide is cheap and requires only basic knowledge of microbiology.
Bioherbicides Using Pathogenic Fungi
Biological control of weeds (herbs) is the deliberate use of its natural enemies to control their growth. According to Alan K. Watson of the Plant Science Department at McGill University, Canada, successful bioherbicide development has occurred for weeds like water hyacinth and water fern, strangler vine, northern jointvetch, round-leaved mallow and dodder. Fungi like Phytopthora palmivora and Colletotrichum gloeosporioides have been successfully used in the control of weeds.
Dr. Watson has pointed out a successful experiment in which a fungal pathogen,Puccinia chondrillina, (of the weed Chondrilla juncea, which occurs in wheat fields) had spread over most of eastern Australia in the period of nine months after it was liberated, and is estimated to be saving the wheat industry $10-20 million per year, without any need for extra inputs.
Bioinsecticides Using Bacteria and Fungi
Bacillus thuringiensis (BT) produces a proteinic toxin which it releases inside the gut of the insect after being ingested. Once inside the gut, the toxin induces paralysis of the midgut and brings about cessation in feeding. This ultimately results in the death of the insect. In his FAO document, Professor V. Taborsky of University of Agriculture, Prague, Czechoslovakia enlists the main sources for the production of BT preparations as strains of the subspecies kurstaki, galeriae and dendrolimus.
Another promising candidate, according to Professor Taborsky, for the control of insect pests is the fungus Metarhizium anisopliae. It has been successfully used for the control for the insect pest Clones punctiventris, the sugarcane spittlebug, Mahanarva postica and Colorado beetle Leptinotarsa decemlineata. This fungus attaches to the cuticle of the insect and penetrates the host exoskeleton. Once inside the host body, it produces chemicals called destruxins, which ultimately cause the death of the insect.
Current Scenario and Future of Biopesticides
At present there appears to be a situation in which biocontrol agents would provide a viable commercial option, where conventional chemical control does not give sufficient control or where there is a case of insecticide resistance; where conventional chemicals are too expensive; or where government restricts application of chemicals. This is because either there is still no awareness as far as hazards of chemical pesticides are concerned or there is general disillusionment as to the efficacy of biocontrol methods.
Whatever the scenario, further research and development of biological pest control methods must be given high priority and people in general and agriculturists in particular must be educated about the dangers posed by handling and use of chemical pesticides. The general public should also demand farm products where chemical pesticides are not used. All this will lead to a general enlightenment about the benefits of biopesticides and will force governments to make policy decisions reducing the use of chemical pesticides and increasing the use of a green alternative.
