Introduction to biopesticides
Biopesticides are biological agents used to control pest populations.They include botanicals, pathogenic microbes such as fungi, bacteria, viruses, other natural enemies of pests such as parasitoids, predators, nematodes and semiochemicals.
Biopesticides can be divided into three major categories.
1. Microbial pesticides
These consist of microorganisms as the active ingredient. Microbial pesticides can control many kinds of pests. However, the active ingredient of the biopesticide is relatively specific for its target pest.
E.g., Bacillus thuringiensis: each strain of this bacterium produces a different mix of proteins that specifically kills one or few related species of insect larvae.
2. Biochemical Pesticides
These are naturally occurring substances that control pests by non–toxic mechanisms in contrast to conventional pesticides that either kill or inactivate pests.
E.g., Sex pheromones, various scented plant extracts that interfere with the mating behavior of pests.
3. Plant-incorporated protectants (PIPs)
This is where plants produce certain pesticidal constituents by themselves from genetic material that are inserted to the plant genome.
E.g., Scientists can extract the gene for the Bacillus thuringiensis (Bt.) pesticidal protein and introduce the gene into the plant genome. Thereby, the plant can manufacture the particular pesticidal protein that inhibit the pest when it feeds on the plant.
An insight to microbial biopesticides
In this category, the active ingredient is a microorganism that either occurs naturally or is genetically engineered.
The pesticide action may be from the organism itself or from a substance it produces. The most commonly used microbial biopesticides are the living organisms which are pathogenic for the pest of interest. They include,
(i) Biofungicides (E.g., Trichoderma, Pseudomonas, Bacillus)
(ii) Bioherbicides (E.g., Phytophthora)
(iii) Bioinsecticides (E.g., Bacillus thuringiensis)
The active ingredient of the microbial pesticide (which is a microorganism such as bacterium, fungus, virus, protozoa, alga, rickettsia, mycoplasma or nematode) suppresses pests either by producing toxic metabolites, competition, or various other modes of action.
An example for a microbial biopesticide; Bacterial biopesticides
Bacterial biopesticides are the most common form of microbial pesticides that function in multiple ways. Generally, they are used as insecticides, although they can be used to control the growth of plant pathogenic bacteria and fungi.
As an insecticide, they are generally specific to individual species of moths, butterflies, beetles, flies, and mosquitoes. To be effective, they must come into contact with the target pest and may require to be ingested. In insects, bacteria disrupt the digestive system by producing endotoxins that are often specific to the particular insect pest.
When used to control a pathogenic bacteria or fungus, the bacterial biopesticide colonizes the plant and crowds out the pathogenic species. The most widely used microbial pesticides are subspecies and strains of B. thuringiensis during its sporulation synthesizes crystalline infusions containing proteins known as endotoxins or Cry proteins, which have insecticidal properties.
Due to their high efficiency and safety in the environment, B. Thuringiensis and Cry proteins are considered as sustainable alternatives to chemical pesticides for the control of insects.
References
Ruiu, L. (2018). Microbial Biopesticides in Agroecosystems. Agronomy, 8(11), 235. https://doi.org/10.3390/agronomy8110235
What are Biopesticides? | US EPA. US EPA. (2022). Retrieved from https://www.epa.gov/ingredients-used-pesticide-products/what-are-biopesticides.
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