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Questions and Answers
The high specificity of microbial insecticides means they target a specific species or group of insects, allowing other harmful ______ to survive.
The high specificity of microbial insecticides means they target a specific species or group of insects, allowing other harmful ______ to survive.
pests
Some microbial insecticides can be affected by environmental factors such as high temperatures and exposure to ______ radiation.
Some microbial insecticides can be affected by environmental factors such as high temperatures and exposure to ______ radiation.
ultraviolet
The most successful commercial bioinsecticide produced by microorganisms is the ______ toxin, which is effective against certain insects.
The most successful commercial bioinsecticide produced by microorganisms is the ______ toxin, which is effective against certain insects.
Bt
The binding of the active toxin to specific receptors in the midgut leads to an ______ in ion concentration, causing cell damage.
The binding of the active toxin to specific receptors in the midgut leads to an ______ in ion concentration, causing cell damage.
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Preparation of Bt toxin suspension requires a ______ broth medium for inoculation with Bacillus thuringiensis.
Preparation of Bt toxin suspension requires a ______ broth medium for inoculation with Bacillus thuringiensis.
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Microbial insecticides are highly specific to a single group or species of ______.
Microbial insecticides are highly specific to a single group or species of ______.
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Microbial insecticides do not negatively impact ______ insects in treated crops.
Microbial insecticides do not negatively impact ______ insects in treated crops.
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The residues of microbial insecticides have no harmful effect on ______ or other animals.
The residues of microbial insecticides have no harmful effect on ______ or other animals.
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The primary mechanism of Bt toxin involves the ______ of the insect gut.
The primary mechanism of Bt toxin involves the ______ of the insect gut.
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Once the Bt toxin invades the insect's gut, it leads to the ______ of the pathogen within the host.
Once the Bt toxin invades the insect's gut, it leads to the ______ of the pathogen within the host.
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One disadvantage of microbial insecticides is that they may have limitations that require users to select effective ______ and application methods.
One disadvantage of microbial insecticides is that they may have limitations that require users to select effective ______ and application methods.
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Microbial insecticides are considered ______ because they come from natural sources and are safe for non-target organisms.
Microbial insecticides are considered ______ because they come from natural sources and are safe for non-target organisms.
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Many microbial insecticides are derived from ______ organisms such as bacteria, fungi, and viruses.
Many microbial insecticides are derived from ______ organisms such as bacteria, fungi, and viruses.
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The active toxin of Bacillus ______ is not formed in the acidic pH found in the intestinal tract of mammals.
The active toxin of Bacillus ______ is not formed in the acidic pH found in the intestinal tract of mammals.
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BT plants express cry genes from B. ______ to provide insect tolerance.
BT plants express cry genes from B. ______ to provide insect tolerance.
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The ______ concentration (LC50) is the lethal concentration of a substance that kills 50% of the population within a specific time.
The ______ concentration (LC50) is the lethal concentration of a substance that kills 50% of the population within a specific time.
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In a bioassay, mortality is calculated using Abbott's ______, a formula to correct control mortality.
In a bioassay, mortality is calculated using Abbott's ______, a formula to correct control mortality.
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One advantage of microbial insecticides is their specific action against ______, making them safer for non-target organisms.
One advantage of microbial insecticides is their specific action against ______, making them safer for non-target organisms.
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The ______ dose (LD50) refers to the amount of a substance required to kill 50% of the population in a specific time.
The ______ dose (LD50) refers to the amount of a substance required to kill 50% of the population in a specific time.
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Preparing a spores and crystals suspension in ______ water is part of the process for bioassays.
Preparing a spores and crystals suspension in ______ water is part of the process for bioassays.
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Bt toxin is considered harmless to humans and mammals because of its ______ in action.
Bt toxin is considered harmless to humans and mammals because of its ______ in action.
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Study Notes
Bioinsecticides - Bt Toxin
- Bioinsecticides are biochemical pesticides derived from natural sources like animals, plants, and microorganisms.
- They are living organisms or their products (phytochemicals, microbial products) used to control pests harmful to crops.
- Microbial pesticides come from naturally occurring or genetically modified microorganisms like bacteria, fungi, algae, and viruses.
- The effect of microbial entomopathogens involves invasion of the insect gut, multiplication of pathogens, insecticidal toxin production, and insect death.
Advantages of Microbial Insecticides
- Highly specific to target insect groups or species, reducing harm to beneficial insects and other organisms.
- Microorganisms used are typically non-toxic and non-pathogenic to humans, animals, and other insects not closely related to the target.
- Suitable for application to crops ready to eat, as residues have no harmful effect on humans or animals.
Disadvantages of Microbial Insecticides
- High specificity can lead to other harmful pests surviving in treated areas.
- Effectiveness is impacted by factors like high temperatures, desiccation, ultraviolet radiation, requiring careful timing and application procedures.
- Some microbial pesticides require specific formulations and storage methods to maintain their efficiency.
Bt Toxin - Details
- The most successful commercial bioinsecticide produced by microorganisms is Bt toxin, also known as 8-endotoxins or Cry protein.
- Bt toxin is a protein produced by Bacillus thuringiensis.
- It's a larvicide toxin, appearing as a parasporal crystal, produced during sporulation, released with spores, and effective against insects with alkaline pH midguts.
- Cry genes are often located on a plasmid in most B. thuringiensis strains.
Bt Toxin Mode of Action
- Cry Endotoxin (inactive toxin) is inactivated until it dissolves after the alkaline pH.
- Gut proteases (trypsin-like proteases) convert the inactive toxin into its active form, Polypeptide toxin.
- The active toxin binds to specific receptors on epithelial cells in the midgut of the target insect.
- Insertion into the cells disrupts ion concentration, causing epithelial cell swelling, and basement membrane destruction.
- Release of gut contents leads to paralysis and larval death.
Bt Toxin Preparation
- Preparation involves using a sterile broth medium, inoculating it with B. thuringiensis, incubating at 30°C for 48 hours, and centrifuging the mixture.
- A supernatant then is separated from the spores and crystals of the Bt toxin, and will be washed to be ready as a suspension (spores and crystals).
- The spore-crystal mix would then go into a suspension in distilled water.
Bioassay - Definition and Types
- A bioassay is a scientific experiment to detect or measure the effects of a substance (toxin) on a living organism.
- Qualitative bioassays estimate the physical effects of a substance.
- Quantitative bioassays determine the concentration of a substance that causes a specific effect, such as killing 50% of a population (LC50).
Bioassay of Bt Toxin - Procedure
- Procedure for a quantitative bioassay of Bt toxin includes 100 ml of water, 10 larvae, starving them, adding food and a defined volume of spore-crystal suspension (toxin), and incubating at room temperature.
- Mortality is calculated using Abbott's formula for correcting control mortality.
Bt Toxin Harmlessness
- Bt toxin is harmless to mammals and humans because of its specificity and the lack of active toxin formation in the low pH of the mammalian intestinal tract.
Bt Toxin in Transgenic Plants
- Bt plants are genetically modified crops with insect tolerance, expressing Cry genes from B. thuringiensis, resulting in delta endotoxin production.
Bt Toxin in Approved Crops
- Potato plants producing Bt toxin were approved in 1995 in the USA.
- Genetically modified maize producing Bt Cry protein was approved in 1996, targeting European corn borer.
- In India, by 2014, using Bt cotton was commonplace in large quantities by farmers.
Microbial Insecticides - Ecological Safety
- Microbial insecticides are ecologically safe because they are highly specific to target insects and do not harm humans or animals.
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Description
This quiz explores bioinsecticides, focusing on Bt toxins derived from natural sources. It highlights the advantages and disadvantages of microbial insecticides, including their specificity and safety for non-target organisms. Test your understanding of these environmentally friendly pest control methods.
