AGRICULTURE IS facing destructive activities of pests and weeds resulting in dramatic loss of productivity. Advancement in fertilizer and pesticides resolved these crises to great extent. But the overuse of these substances sometime leads to serious threats for soil environment and crops and damaging microbial population in soil and also resistance is produced in pests against these pesticides. Moreover the persistent time of residues of these pesticides is very high. The gradual reduction in the use of pesticides in agriculture without effecting the quantity and quality of crops production can only be possible if new technologies are adopted that are economically attractive, easily degradable and environmental friendly pesticides. Sustainable agriculture is the system in which crop yield is obtained with exploiting the natural resources.
Biopesticides are substances of pesticidal activities and considered as low risk compounds obtained from natural resources e.g. animals, plants, bacteria, fungi or mineral source, garlic, mint and canola oil. These biopesticides provides protection against pest and soil borne diseases. The key component in integrated pest management (IPM) is biopesticides. There are four types of biopesticides a) Microbial biopesticides b) Plant incorporated protectant c) Biochemical pesticides and d) RNAI pesticides. Another classification of these biopesticides, the natural source from which they are obtained, is classified as microbial pesticides, botanical pesticides, zooid pesticides and genetically modified plants. Out of 1 million species of insects, 15,000 are considered as pest and most of them pathogenic microorganism is associative with them and hence controlled naturally. More than 300 species of pest requires some sort of control. The biopesticides obtained from Bactria, viruses, protozoa and nematods are considered as microbial biopesticides. Bacteria are the most potent among bioagents. Due to pathogenicity basis bacteria have four groups but crystalliferous spore forming bacteria is most effective. B. thuringiensis is the example of spore forming bacteria with 6000 isolates stored in all over the world. Bt producealpha and beta exotoxins and delta endotoxins toxins that paralyze the digestive system of pest. Formulation of Bt depends on the properties of pest, soil physical, chemical and biological properties and environmental factors also effect it. The toxic crystal of Bt is commercially affected by eaten by insect gut at specific pH (alkaline pH) at specific temperature. It damages the gut lining and cause paralyzed the insect. It is quite stable and sensitive to heat, so protective measure should be taken during storage.
Viral biopesticides are host specific and efficiency can be seen among 1600 viruses and effective especially caterpillar insects. Most popular viral biopesticide belong to baculoviruses family. Viruses enter in insects body through gut. First virus enters in to tissue and replicate there. It lay eggs there and feeding and by movements viruses disturb the insect physiology. Within 3-8 days the insect died due to viral infection. Genetic modification can be used to increase its killing efficiency.
750 are entomopathogenic fungi but 20 have serious attention as bio-control gents are known, the fungi invade the exoskeleton/ cuticle of the pest by direct penetration. Fungi degrade these cuticles by releasing extracellular as well as intracellular enzymes. Death of host occurs due to tissue damages and through toxins. Fungus came out of the insect body after producing spores in insect body. These spores spread through wind or water can cause infection in insects.
Many substances are produced by plants genetically that have pesticidal activities. Sometimes foreign material/ particle are introduced in plants and then plants able to produce resistant against the specific organisms. Bt protein is introduced in the genetics of plant material. As a response the plant produces the substance that shows resistance against pasts and disease.
Biochemical pesticides are natural substances that are produced by plant itself to control pest. It is the nontoxic mechanisms of pest control. These include substances that interfere with insect mating e.g. Allellochemicals and phytohormones. Hence no change of natural biological and ecological cycle. In this way pest population is controlled because further pest generations are not possible. RNA interference is recent technology and understudy for possible use as spray on pests. Similarly the efficiency bioagents can be improved through recombinant DNA technology. RNA is fragile molecule that degrades within days or week after application. It does not modify the genome of plant.
Biopesticides have many advantages 1) environmental friendly 2) No harmful residues detected 3) Cheaper than chemical pesticides when locally produced. 4) More effective than chemical pesticides in the long-term 5) short biodegradable period. While it has some disadvantages 1)Slow speed of action 2) Inconsistency due to the influences of various biotic and abiotic factors 3) Lack of expertise 4) Lack of good microbes testing laboratories
Conclusion: Pesticides are chemical substances that kill insect by chemical action, shelf life and wide spectrum of activity, fast in killing. Frequently excessive use of these chemical have adverse effect on soil microbial ecology and also for environment. While biopesticides have small shelf life and easily degradable, high target specificity, promote beneficial microbe population. They are environmental friendly and less toxic.