Question:
Effect of pyrethrum on mosquitoes is described as
Effect of pyrethrum on mosquitoes is described as
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Pyrethrum is famous for causing fast, temporary insect paralysis, not for long lasting surface action.
Updated On: Jul 7, 2026
- Residual
- Repellent
- Knock down
- Contact
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The Correct Option is C
Solution and Explanation
Step 1: Recall what pyrethrum is.
Pyrethrum is a natural insecticide taken from the dried flowers of the Chrysanthemum plant. It acts on the sodium channels of an insect's nerve cells, causing repeated firing and rapid paralysis.
Step 2: Recall the term used for this effect.
This fast paralysis, seen within seconds to minutes of exposure, is called the knock down effect. It is the hallmark property pyrethrum is known for in vector control, this is why space spraying with pyrethrum is used to get a quick, visible fall of mosquitoes.
Step 3: Compare with the other choices.
Residual effect means the insecticide stays active on a surface for a long time after spraying, which is a strength of DDT, not pyrethrum, since pyrethrum breaks down fast in sunlight and air.
Repellent action means keeping insects away without killing them, which describes agents like DEET, not pyrethrum.
Contact only describes the route by which an insecticide enters the insect body, through the outer cuticle, which is true of many insecticides in general and is not the specific, named effect this question is asking about.
Step 4: Final answer.
The property that pyrethrum is specifically described by is \[ \boxed{\text{Knock down effect}} \]
Pyrethrum is a natural insecticide taken from the dried flowers of the Chrysanthemum plant. It acts on the sodium channels of an insect's nerve cells, causing repeated firing and rapid paralysis.
Step 2: Recall the term used for this effect.
This fast paralysis, seen within seconds to minutes of exposure, is called the knock down effect. It is the hallmark property pyrethrum is known for in vector control, this is why space spraying with pyrethrum is used to get a quick, visible fall of mosquitoes.
Step 3: Compare with the other choices.
Residual effect means the insecticide stays active on a surface for a long time after spraying, which is a strength of DDT, not pyrethrum, since pyrethrum breaks down fast in sunlight and air.
Repellent action means keeping insects away without killing them, which describes agents like DEET, not pyrethrum.
Contact only describes the route by which an insecticide enters the insect body, through the outer cuticle, which is true of many insecticides in general and is not the specific, named effect this question is asking about.
Step 4: Final answer.
The property that pyrethrum is specifically described by is \[ \boxed{\text{Knock down effect}} \]
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