BY: RAHUL ANDHARIA (MSIWM001)
- Biocontrol agents or Compounds used for managing agricultural pests by means of specific biological effects are termed as Biopesticide.
- Natural bio-control agents such as plants, certain minerals, microorganisms can be used as biopesticides by modifying them.
- Majority of crop loss is due to pests or insects. As biopesticides has less adverse effects on environment compared to traditional insecticides, hence can be used to control pests.
- Some of the earliest agricultural biopesticides used were plant extracts such as Nicotine during 17th century as reported in records.
- In the year 1835, demonstration experiments involving biological control agents against Lepidopteron pests were carried by Agostine Bassi in White muscardine disease caused by a fungus Beauveria bassiana.
- In the 20th century, studies involving use of biopesticides emerged rapidly and more number of biopesticides was developed. Bacterium Bacillus thuringenesis was considered to be the initial biopesticide.
Key features of bio-control agents used as biopesticides:
- It should be specific to the target host.
- It should have high multiplication rate.
- It should be environment friendly with very less adverse effects.
Types of Biopesticides:
Three main types of biopesticides are used commonly:
Microorganisms used for insect control are called as bioinsecticides. Viruses, bacteria, fungi, protozoa and mites can be used as bioinsceticides.
- Bacterial biopesticides:
- Several different bacterial pathogens specific to type of insect they control are being used as insecticides. Examples: Bacillus, Clostridium, Pseudomonas, Enterobacter, Proteus, etc can be used.
Bacillus Thuringenesis: spore forming, rod shaped, gram positive bacterium. They produce parasporal crystals during sporulation. These crystals can be called as Cry proteins or delta endotoxins. These cry proteins prove to be toxic to insects, specifically to lepidopteron and coleopterans.
Mode of action of Bt:
- Parasporal crystals containing cry proteins are ingested by the insects.
- Once ingested, these crystals get dissolved in the alkaline environment of the gut of the insect.
- Delta toxin which is inactive gets cleaved and thus is activated.
- Specific receptors in the midgut respond to the toxins and binds with it.
- Pores develop in the epithelium layer of the insect as soon as toxin is inserted.
- Thus, epithelium is disrupted leading to cell lysis and death of insect.
Symptoms: Common symptoms include; larvae become static and sluggish, stops feeding, water oozes out from larval bodies, and finally larvae dies and falls off the leaf. Bt cotton works particularly against cotton Bollworms, gypsy moths and cabbage worms.
- Fungal biopesticides:
- Generally, Entomopathogenic fungi are used as biopesticides. Common examples are Beauveria bassiana (causes White muscardine disease) and Metarhizium anisopliae(causes green muscardine disease).
Mode of action of Beauveria bassiana:
- It is a filamentous fungus. It is also called as imperfect fungi and belongs to class Deuteromycetes. Generally, used against American boll worm, Codling moth and Potato beetle.
- By using spores, fungus invades haemocoel of Insects.
- Spores germinate once they attach to the cuticle. Hyphae penetrates insect cuticle.
- Penetration appresorium and penetration Peg is formed which helps in the penetration process.
- Fungal enzymes like chitinases, proteases, and lipases helps to dissolve the cuticle. Once the cuticle is dissolved, hyphae enter the haemolymph and proliferate and colonise the entire insect and release blastospores.
- Due to depletion of nutrition in haemolymph, insect dies.
- Viral biopesticides:
- They attack arthropods and other insects. Commonly used viral biopesticide is Baculoviruses. Viral biopesticides are generally used to control lepidopteron larvae. Baculoviruses are composed of double stranded DNA and are very small viruses. Three subgroups are present in these viruses; Nuclear Polyhedrosis virus (NPV), Granulosis virus (GV), and Non Occluded viruses.
Mode of action of NPV:
- When insect ingests the virus, it enters the mid-gut of insects and infects the gut cells by membrane fusion.
- In the nucleus, NPV un-coats itself and passes through the intestinal epithelium.
- Infects the haemocoel.
Symptoms: includes; discoloration of larvae (turns yellow or brown), larval decomposition, infected larvae hangs itself upside down on twigs and larvae becomes swollen because of accumulation of viral fluid inside them.
- Many fungi are known from genera like Dactylella, Arthrobotrys which can act as nematicide.
Fungus damage nematode in different ways:
- Haustoria: fungi use these haustoria to penetrate into the body of the nematode and then it digests cell contents and uptakes nutrients of the nematode.
- Catching by loop: loops are formed by fungal mycelium. When nematode passes through the loop, it constricts and gets trapped.
- Production of adhesive hyphae: adhesive branches are produced by fungal mycelium which may stick with the nematodes body.
- Hyphal mesh formation: mesh like cobweb is formed to tap the nematode.
- The other groups which can acts as nematicide are soil fungi like Verticillium Chlamydosporium, Dactylella oviparisitica.
- They are primarily used to control the weeds and include use of phytotoxins, pathogens and microbes.
- Living microorganism is the active ingredient in bio-herbicide.
- Most commonly fungi are used, though bacteria can also be used as bio-herbicides.
- High degree of target specifity against weed can be obtained using bio-herbicides.
- Bio-herbicides have no effect on non-target and beneficial plants and hence are used frequently.
Examples: fungi like Phragmidium violacerum, Phytopthora palmivora (targets milk-weeds) are used commonly.
Advantages of Biopesticides:
- Less toxic compared to conventional pesticides.
- The main advantage of using biopesticide is that they only affect target pest.
- It provides correct identification of pest as biopesticides are highly specific.
- Relatively cheaper.
- The risk of pests developing resistance to biopesticides is low as mostly the agents used have multiple mode of action.
Few limitations of biopesticides:
- When compared to conventional pesticides, they have a slower rate of control and lower efficacy and shorter persistence.
- Biopesticides have much greater susceptibility to environmental conditions. This can be avoided by modifying the organism used but the process will be time consuming and costly.
- Grower must require greater knowledge to use biopesticides effectively as they are not as robust as conventional pesticides.