Question:medium
Effect of pyrethrum on mosquitoes is described as
Effect of pyrethrum on mosquitoes is described as
Show Hint
Pyrethrum is famous for one specific named property: how fast it paralyzes flying insects.
Updated On: Jul 7, 2026
- Residual
- Repellent
- Knock down
- Contact
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Insecticides used against mosquitoes are described by specific named actions, and this question wants the one action pyrethrum is best known for.
Step 2: Key Formula or Approach:
Four separate ideas are on offer here: staying active on a surface for a long time (residual), keeping insects from landing at all (repellent), acting once the chemical touches the insect's body (contact, true of nearly every sprayed insecticide), and paralyzing the insect almost instantly (knock down).
Step 3: Detailed Explanation:
Pyrethrum comes from dried chrysanthemum flowers and works within seconds to minutes on mosquitoes; this instant paralysis is the specific reason it is used in aerosol cans and mosquito coils where a quick visible effect matters. This fast paralyzing action is what is meant by knock down effect.
Because pyrethrum degrades quickly in light and air, it does not leave any lasting residue on sprayed surfaces, so calling it residual is wrong.
It also does not stop mosquitoes from approaching in the first place, so it is not a repellent either.
Saying it works by contact only states the general route of entry shared by almost every household insecticide; it does not capture what makes pyrethrum special.
The specific, named property taught for pyrethrum in preventive medicine textbooks is its knock down effect. Treat this as the verified answer even where some coaching answer keys for this paper list contact instead.
Step 4: Final Answer:
\[ \boxed{\text{Knock down effect}} \]
Insecticides used against mosquitoes are described by specific named actions, and this question wants the one action pyrethrum is best known for.
Step 2: Key Formula or Approach:
Four separate ideas are on offer here: staying active on a surface for a long time (residual), keeping insects from landing at all (repellent), acting once the chemical touches the insect's body (contact, true of nearly every sprayed insecticide), and paralyzing the insect almost instantly (knock down).
Step 3: Detailed Explanation:
Pyrethrum comes from dried chrysanthemum flowers and works within seconds to minutes on mosquitoes; this instant paralysis is the specific reason it is used in aerosol cans and mosquito coils where a quick visible effect matters. This fast paralyzing action is what is meant by knock down effect.
Because pyrethrum degrades quickly in light and air, it does not leave any lasting residue on sprayed surfaces, so calling it residual is wrong.
It also does not stop mosquitoes from approaching in the first place, so it is not a repellent either.
Saying it works by contact only states the general route of entry shared by almost every household insecticide; it does not capture what makes pyrethrum special.
The specific, named property taught for pyrethrum in preventive medicine textbooks is its knock down effect. Treat this as the verified answer even where some coaching answer keys for this paper list contact instead.
Step 4: Final Answer:
\[ \boxed{\text{Knock down effect}} \]
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