BIOPESTICIDES

 Biopesticides

• Biopesticides are the types of natural pesticides derived from such natural materials as animals, plants, microorganisms, and certain minerals.
• The term Biopesticides defines compounds that are used to manage insect pests by means of specific biological effects rather than as broader chemical pesticides
• Biopesticides can be used to eliminate several different types of pests from Agricultural crops.
• Biopesticides is a broad term and includes Bioinsecticides, Biobactericides, Biofungicides, Bioherbicides and Bionematicides.
• Biobactericides and Biofungicides are combinedly referred as Biocontrol agents.

 

Classes of Biopesticides

a) Biochemical Biopesticides

• Biochemical pesticides are naturally occurring substances that control pests by non-toxic mechanisms. Conventional pesticides, by contrast, are generally synthetic materials that directly kill or inactivate the pest.
• Biochemical pesticides include substances that interfere with mating (insect sex pheromones) and attract insect pests to traps (plant extracts).
• Biochemical pesticides are further classified into different types depending upon whether they function in controlling infestations of insect pests by exploiting (i) Pheromones (semiochemicals), (ii) Plant extracts/oils or (iii) Natural insect growth regulators.

i) Pheromones

• Pheromones are chemicals produced by insects which are used in controlling insects in the Integrated Pest Management (IPM) programs.
• Pheromones are effective in disrupting insect mating to prevent the success of mating, thus reducing the number of insect progeny.
• Insect pheromones are not true ‘insecticides’ since they do not kill insects but influence their olfactory system to affect behaviour.

ii) Plant based extracts or Essential oils

• Plant-based extracts and Essential oils have emerged as attractive alternatives to synthetic insecticides for Insect Pest Management.
• Plant-based extracts and Essential oils are naturally occurring insecticides as they are derived from plants and contain a range of bioactive chemicals.
• Depending on physiological characteristics of insect species as well as the type of plant, plant extracts and essential oils exhibit a wide range of action against insects:

ü  Act as repellents, attractants, or antifeedants.

ü  Inhibit respiration, hamper the identification of host plants by insects.

ü  Inhibit oviposition and decrease adult emergence by ovicidal and larvicidal effects.

iii) Insect Growth Regulators (IGRs)

• Insect Growth Regulators (IGRs) inhibit certain fundamental processes required for the survival of insects, thereby killing them. Furthermore, these compounds are highly selective and less toxic to non-target organisms.
• Depending on the mode of action, IGRs had been recently grouped in Chitin Synthesis Inhibitors (CSIs) and substances that interfere with the action of insect hormones (i.e., juvenile hormone analogues and ecdysteroids).
• IGRs can control many types of insects including fleas, cockroaches, and mosquitos even though they are not so fatal for adult insects. Although low in toxicity to humans, they prevent reproduction, egg-hatch, and molting from one stage to the next in the young insects, while mixing them with other insecticides is able to kill even the adult insects

b) Microbial Biopesticides

• Microbial pesticides contain microorganisms (Entomopathogens) such as protozoan, viruses, fungi and bacteria as active ingredients. The active compounds isolated from these microorganisms attack specific pest species.
• Microbial pesticides can control many different kinds of pests, although each separate active ingredient is relatively specific for its target pests. For example, there are fungi that control certain weeds (Bioherbicides) and other fungi that kill specific insects (Bioinsecticides).
• The most widely used bacterial biopesticide against insect pests is Bacillus thuringiensis (Bt). This bacterium produces an Insecticidal Protein Crystal (IPC) that can be sprayed against pest targets.
• Major groups of bacterial entomopathogens include species of Pseudomonas, Yersinia, Chromobacterium, etc., while fungi comprise species of Beauveria, Metarhizium, Verticillium, Lecanicillium, Hirsutella, Paecilomyces, etc.
• Other important microbial pesticide producers are Baculoviruses that are species specific and their infectivity is associated with the crystalline Occlusion bodies that are active against chewing insects (Lepidopteran caterpillars)
• Entomopathogenic nematodes used as biocontrol agents belong primarily to species in the genera Heterorhabditis and Steinernema, associated with mutualistic symbiotic bacteria of the genera Photorhabdus and Xenorhabdus and are safe to mammals, environment, and non-target organisms.
• The commercial development of Microbial biopesticides has been convenient because of their ease in mass production, using in vivo or in vitro techniques.

c) Plant-Incorporated-Protectants (PIPs)

• Plant-Incorporated-Protectants (PIPs) are the genes and proteins, which are introduced into plants by Genetic engineering. They allow the genetically modified plant to protect itself from pests, like certain insects or viruses.
• For example, some plants produce insect-killing proteins within their tissues. They can do this because genes from Bacillus thuringiensis were inserted into the plant’s DNA. Different types of proteins target different types of insects. 

Types of Microbial Insecticides (Entomopathogenic Microorganisms)

Some of the commonly used Microbial Biopesticides are

a)     Bacterial Bioinsecticides (Entomopathogenic Bacteria)

§  Bacillus thuringiensis

§  Bacillus sphaericus (Mosquito control)

§  Paenibacillus popilliae

b)     Viral Bioinsecticides (Entomopathogenic Virus)

§  Cydia pomonella granulosis virus (CpGv)

§  Nucleopolyhedrovirus (NPV)

c)     Fungal Bioinsecticides (Entomopathogenic Fungi)

§  Beauveria bassiana

§  Isaria fumosorosea

§  Lecanicillium lecanii

§  Lecanicillium longisporum

§  Metarhizium anisopliae

§  Hirsutella thompsonii

d)     Protozoan Bioinsecticides (Entomopathogenic Protozoa)

§  Nomasa locustae

 

Biocontrol agents (Plant Disease Control Agents)

• Plant diseases need to be controlled to maintain the quality and abundance of food, feed, and fiber produced by growers around the world.
• The terms “Biological control” and its abbreviated synonym “Biocontrol” have been used in different fields of Biology, most notably Entomology and Plant pathology.

ü  In Entomology, it has been used to describe the use of live Predatory insects, entomopathogenic nematodes, or microbial pathogens to suppress populations of different pest insects.

ü  In Plant pathology, the term applies to the use of microbial Antagonists to suppress diseases as well as the use of host-specific pathogens to control weed populations.

• In both fields (Entomology and Plant pathology), the organism that suppresses the pest or pathogen is referred to as the Biological Control Agent (BCA).
• About 30 % of the yield in agriculture is lost because of the combined effects of biotic and abiotic stresses, with pathogenic fungi alone responsible for a reduction of about 12 %.
• Phytopathogens can act as Root pathogens, Stem pathogens, Leaf pathogens, Flower pathogens and Fruit pathogens.
• Biological control using microbial antagonists has received a great deal of attention as an alternative and promising measure to control different plant diseases.
• Most research and development efforts have focused on isolates of three genera, Bacillus subtilis, Pseudomonas fluorescence and Trichoderma sp.
• Biological control, using microorganisms to suppress plant disease, offers a powerful alternative to the use of synthetic chemicals. The rich diversity of the microbial world provides a seemingly endless resource for this purpose.
• The use of Biological control agents, alone or in combination with other management measures, has gained attention over the past decades, driven by the need to seek for sustainable and eco-friendly alternatives to confront plant pathogens.

Advantages of Microbial Biopesticides

• Biopesticides important components of Integrated Pest Management (IPM) programmes, and they are said to be a safer (non-toxic) alternative to synthetic chemicals.
• Biopesticides have a narrow target range and a very specific mode of action. Biopesticides affect only the target pest and closely related organisms. But, conventional pesticides that may affect organisms such as birds, insects and mammals.
• Biopesticides are often effective in small quantities.
• Biopesticides decompose quickly and do not leave problematic residues.
• Biopesticides are safer to humans and less toxic to the environment when compared to conventional pesticides.
• Cost wise Biopesticides are cheaper than the Chemical pesticides.