**Core Concept**
Paris green is a toxic substance used in the control of mosquito larvae, particularly those of the Anopheles species responsible for malaria transmission. Its mechanism of action involves disrupting the larval nervous system.

**Why the Correct Answer is Right**
Paris green acts as a stomach poison for mosquito larvae, causing their death by interfering with their nervous system function. When ingested, it is absorbed into the larval body and exerts its toxic effects. The precise mechanism involves the disruption of the larval nervous system, leading to paralysis and ultimately death.

**Why Each Wrong Option is Incorrect**
**Option A:** DDT is a contact poison, not a stomach poison. It works by disrupting the insect's nervous system upon contact, rather than after ingestion.
**Option C:** Pyrethrum is a natural insecticide derived from the flowers of Chrysanthemum cinerariaefolium. While it is toxic to insects, it is not typically used as a stomach poison for mosquito larvae.
**Option D:** Antilarva oil is not a widely recognized or established substance for controlling mosquito larvae. Its efficacy and mechanism of action are not well-documented.

**Clinical Pearl / High-Yield Fact**
Paris green is an example of a larvicide, a type of insecticide that targets the larval stage of an insect's life cycle. This is an important concept in the control of mosquito-borne diseases, such as malaria.

**Correct Answer:**
✓ Correct Answer: B. Paris green