Rotenone is an odorless, colorless, crystalline isoflavone used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the seeds and stems of several plants, such as the jicama vine plant, and the roots of several members of Fabaceae. It was the first described member of the family of chemical compounds known as rotenoids. Evidence has come to suggest that rotenone may cause Parkinson's disease to develop from both acute and prolonged exposure.
hence the correct answer is D) a natural insecticide

Rotenone as a Natural Insecticide:
Rotenone is a naturally occurring substance derived from the roots of several tropical plants. It has been used for centuries as an insecticide due to its ability to effectively kill a wide range of insects.

Mechanism of Action:
- Rotenone works by disrupting the function of the mitochondria in insect cells, leading to a buildup of toxic byproducts and ultimately causing cell death.
- It interferes with the electron transport chain, which is crucial for energy production in cells, leading to the insect's inability to generate ATP and eventually causing paralysis and death.

Effectiveness:
- Rotenone is highly effective against a variety of pests such as aphids, mites, beetles, and caterpillars.
- It is particularly useful for organic farming as it is a natural product that breaks down quickly in the environment and poses minimal risk to non-target organisms.

Environmental Impact:
- While rotenone is considered safe for use in organic farming, it is toxic to fish and other aquatic organisms.
- Care must be taken to prevent runoff into water bodies to avoid harming aquatic ecosystems.

Regulation:
- Due to its potential environmental impact, the use of rotenone is regulated in many countries to ensure proper application and minimize negative consequences.
In conclusion, rotenone is a powerful natural insecticide that can be an effective tool for controlling insect pests in a sustainable and environmentally friendly manner when used responsibly.