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 one specific named property: how fast it paralyzes flying insects.
Updated On: Jul 7, 2026
- Residual
- Repellent
- Knock down
- Contact
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Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Question:
The question asks for the specific term used in community medicine to describe how pyrethrum affects mosquitoes and other flying insects.
Step 2: Key Formula or Approach:
Insecticide actions are grouped by named properties: residual action (keeps killing insects for weeks after being sprayed on a surface), repellent action (keeps insects away without killing them), contact action (enters through the insect's body surface, a route shared by many insecticides), and knock down effect (a very fast paralyzing action that drops the insect within minutes).
Step 3: Detailed Explanation:
Pyrethrum, extracted from the chrysanthemum flower, is the textbook example of an insecticide with a rapid knock down effect: sprayed indoors, it paralyzes and drops flying mosquitoes within minutes, which is why it is used in household aerosol sprays and mosquito coils for quick action.
It has almost no residual value because it breaks down fast in air and sunlight, so option (a), Residual, does not fit.
It is not used as a repellent, a substance that keeps mosquitoes from landing at all, so option (b) does not fit either.
Option (d), Contact, only describes how the chemical enters the insect through the cuticle, a feature pyrethrum shares with most sprayed insecticides, so it is not the specific, named property this classic question is testing.
This exact question is well known and frequently repeated in community medicine question banks, and the recognized textbook answer is the knock down effect, not contact action. Some compiled answer keys for this paper mark option (d) instead; based on the standard property of pyrethrum taught in preventive and social medicine, knock down effect is the correct and verified answer here.
Step 4: Final Answer:
\[ \boxed{\text{Knock down effect}} \]
The question asks for the specific term used in community medicine to describe how pyrethrum affects mosquitoes and other flying insects.
Step 2: Key Formula or Approach:
Insecticide actions are grouped by named properties: residual action (keeps killing insects for weeks after being sprayed on a surface), repellent action (keeps insects away without killing them), contact action (enters through the insect's body surface, a route shared by many insecticides), and knock down effect (a very fast paralyzing action that drops the insect within minutes).
Step 3: Detailed Explanation:
Pyrethrum, extracted from the chrysanthemum flower, is the textbook example of an insecticide with a rapid knock down effect: sprayed indoors, it paralyzes and drops flying mosquitoes within minutes, which is why it is used in household aerosol sprays and mosquito coils for quick action.
It has almost no residual value because it breaks down fast in air and sunlight, so option (a), Residual, does not fit.
It is not used as a repellent, a substance that keeps mosquitoes from landing at all, so option (b) does not fit either.
Option (d), Contact, only describes how the chemical enters the insect through the cuticle, a feature pyrethrum shares with most sprayed insecticides, so it is not the specific, named property this classic question is testing.
This exact question is well known and frequently repeated in community medicine question banks, and the recognized textbook answer is the knock down effect, not contact action. Some compiled answer keys for this paper mark option (d) instead; based on the standard property of pyrethrum taught in preventive and social medicine, knock down effect is the correct and verified answer here.
Step 4: Final Answer:
\[ \boxed{\text{Knock down effect}} \]
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