Microbial Insecticides Quiz

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Questions and Answers

What is a major advantage of microbial insecticides?

They are specific to a single group or species of insects. (correct)

They have long-lasting residues on crops.

They are effective against all insects.

They are derived from synthetic chemicals.

Microbial insecticides can be harmful to humans and beneficial insects.

False

What are biopesticides derived from?

Natural sources such as animals, plants, and microorganisms.

Microbial insecticides can be applied on crops that are ready to eat, such as _____ and fruits.

vegetables Signup and view all the answers

Match the following terms with their definitions:

Biopesticides = Derived from natural sources for pest management Microbial insecticides = Pesticides from microorganisms that target specific insects Entomopathogens = Microorganisms that invade and cause disease in insects Toxin production = Process where harmful substances are produced by microbes Signup and view all the answers

What is the primary action of the Bt toxin produced by Bacillus thuringiensis?

It paralyzes the larva and leads to its death. Signup and view all the answers

Microbial insecticides affect both harmful and beneficial insects equally.

False Signup and view all the answers

What environmental factors can affect the efficiency of some microbial insecticides?

High temperatures, desiccation, or exposure to ultraviolet radiation. Signup and view all the answers

The efficient storage of microbial pesticides depends on following the ______ directions provided on the label.

label Signup and view all the answers

Match the following components of Bt toxin action with their function:

Cry Endotoxin = Inactive toxin Gut proteases = Activate the toxin Polypeptide toxin = Active toxin Epithelial cell receptors = Binding site for toxins Signup and view all the answers

What is LD50 in the context of a bioassay?

The lethal dose to kill 50% of the population Signup and view all the answers

Bt toxin is harmful to mammals and humans.

False Signup and view all the answers

What are BT plants?

Transgenic plants or genetically modified crops with insect tolerance expressing cry genes from B. thuringiensis. Signup and view all the answers

The unit of LC50 is ___.

mg/l Signup and view all the answers

What is the first step in preparing a spores and crystals suspension?

Incubating inoculated medium Signup and view all the answers

The ____ is a mathematical equation used to calculate mortality in bioassays.

Abbott's formula Signup and view all the answers

Delta endotoxin is produced in potato plants approved by the Environmental Protection Agency.

True Signup and view all the answers

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 manage pests harmful to crops.
Microbial pesticides come from naturally occurring or genetically modified microbial entomopathogens, including bacteria, fungi, algae and viruses.
The effect of microbial entomopathogens involves the invasion of the insect gut, multiplication of the pathogen, insecticidal toxin production and eventually the death of the insect.

Advantages of Microbial Insecticides

Highly specific to a single pest species or group of insects
Do not directly affect beneficial insects
Microorganisms used in microbial insecticides are essentially non-toxic and non-pathogenic to animals, humans and other insects not closely related to the target pest.
Residues have no harmful effect to humans or other animals; can be used in crops ready to consume (fresh vegetables and fruits).

Disadvantages of Microbial Insecticides

High specificity to only a specific insect species in a treated area; other harmful pests will survive.
Effectiveness affected by environmental factors (high temperatures, desiccation, UV radiation)
Special formulation and storage procedures are necessary for some microbial pesticides to maintain their efficiency

Bt Toxin

The most successful commercial bioinsecticide produced by microorganisms is Bt toxin.
It's called 8-endotoxins, crystal protein or Cry protein.
It's a protein produced by Bacillus thuringiensis.
It's a larvicide toxin.
It appears as a parasporal crystal.
It's produced during sporulation.
Released along with the spores.
Effective against insects with an alkaline pH in their midgut.
In most strains of B. thuringiensis, the cry genes are located on a plasmid.

Mode of Bt Toxin Action

Cry Endotoxin (inactive toxin) in the alkaline pH condition.
Dissolving the crystal and formation of Protoxin.
Gut proteases (trypsin-like proteases) convert Protoxin into Polypeptide toxin (active toxin).
Active toxin binds to specific receptors located on the epithelial cells of the midgut.
Toxin inserts into the cells, causing an imbalance in ion concentrations.
This leads to swelling of epithelial cells, destruction of the basement membrane, release of gut contents into the larva body, and eventually paralysis and death.

Preparation of Bt Toxin Suspension

Sterile broth medium
Inoculating the medium with B. thuringiensis
Incubating the inoculated medium at 30°C for 48 hours.
Centrifugation of the medium
Washing of the sediment
Preparation of spores and crystals suspension in distilled water

Bioassay

Scientific experiment to detect or measure the effects of certain substances (toxins) on living organisms.
Types of bioassays:
- Qualitative: estimating the physical effects of a substance.
- Quantitative: estimating the concentration of a substance.
In quantitative bioassays:
- LD50: lethal dose of a substance to kill 50% of a population in a specified time (unit: g or mg/kg body weight)
- LC50: lethal concentration of a substance to kill 50% of a population in a specified time (unit: mg/l of the toxin).

Bioassay of Bt Toxin

100 ml of water + 10 larvae
Starve the larvae
Add food larvae and definite volume of spore-crystal suspension
Incubate at room temperature
Calculate mortality using Abbott's formula.

Bt Toxin Harmless to Mammals and Humans

The toxin is very specific in its action.
The active toxin is not formed in the acidic pH found in the intestinal tract of mammals.

Bt Toxin in Transgenic Plants (BT plants)

Genetically modified plants with insect tolerance.
Expressing cry genes from B. thuringiensis.
Resulting crops contain delta-endotoxin.

Bt Toxin in Commercial Applications

Potato plants producing Bt toxin were approved in 1995 by the Environmental Protection Agency (first human-modified pesticide-producing crop in the USA).
Genetically modified maize producing Bt Cry protein, approved in 1996, killed the European corn borer and related species.
In India, by 2014, more than seven million cotton farmers adopted Bt cotton, occupying over 26 million acres.

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Description

Test your knowledge on microbial insecticides and their applications in agriculture. This quiz covers their advantages, effects on insects, and the action of the Bt toxin produced by Bacillus thuringiensis. Assess your understanding of biopesticides and environmental factors influencing their efficiency.