UPSC Prelims 2021 Q21: Environment & Ecology – Sustainable Agriculture & Forestry
- (a) Congress grass
- (b) Elephant grass
- (c) Lemongrass
- (d) Nut grass
Answer: (c) Lemongrass
Explanation
Natural Mosquito Repellent Plants
| Plant | Repellent Use? | Active Compound |
|---|---|---|
| Congress grass (Parthenium) | NO - Invasive weed, allergen | None useful |
| Elephant grass (Napier grass) | NO - Fodder crop | None useful |
| Lemongrass (Cymbopogon citratus) | YES | Contains citronella oil, citral, geraniol - proven mosquito repellents. Used in candles, sprays, lotions. |
| Nut grass (Cyperus rotundus) | NO - Weed, used in Ayurveda for other purposes | None useful |
Correct answer: (c) Lemongrass. Citronella oil (extracted from lemongrass) is a WHO-recognised mosquito repellent. Cymbopogon nardus (citronella grass) is a related species also used commercially.
Answer: (c) Lemongrass.
Why each option is right or wrong
- (a) Incorrect. Congress grass (Parthenium hysterophorus) is an invasive weed causing allergies, not a repellent.
- (b) Incorrect. Elephant grass (Napier) is a fodder crop, not a repellent.
- (c) CORRECT. Lemongrass contains citronella oil, citral and geraniol - proven natural mosquito repellents used in candles, sprays and lotions.
- (d) Incorrect. Nut grass has other uses (Ayurveda for digestion, skin) but not as a mosquito repellent.
Key point
Lemongrass = source of citronella oil = natural mosquito repellent. Also contains citral and geraniol. WHO-recognised. Used in candles, sprays. Related plant: Cymbopogon nardus (citronella grass).
Remember
Lemongrass (Cymbopogon citratus) is used in preparing natural mosquito repellents. It contains citronella oil, citral and geraniol - all proven repellents. Congress grass (Parthenium) is an invasive weed. Correct answer: (c).
Common mistakes
- Confusing lemongrass with citronella grass. Both are Cymbopogon species and both yield citronella-family oils.
- Not knowing Congress grass (Parthenium) is an invasive alien species harmful to biodiversity and human health.
- Assuming any aromatic grass is a repellent. Only lemongrass/citronella have proven active compounds.
Exam tip
Natural mosquito repellents: Lemongrass, Neem (azadirachtin), Tulsi, Peppermint, Eucalyptus (PMD/oil of lemon eucalyptus). DEET is the synthetic standard. PMD is WHO-approved alternative to DEET.
Sources
- WHO - Vector Control Guidelines: Botanical Repellents
- ICMR - National Institute of Malaria Research: Herbal Repellents