Cause of decline in population of reptiles and birds is

Options

A. Bioinsecticides
B. Biofertilizers
C. DDT
D. Both A and B

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the cause of the decline in the population of reptiles and birds. This requires us to analyze various factors that could contribute to this decline.

2. **Evaluating Options**: We need to consider the provided options one by one to determine which is responsible for the decline in reptile and bird populations.

3. **Analyzing Bio Insecticides**: The first option is bio insecticides. These are biological agents used to control pests. Since they are not harmful to reptiles and birds, this option can be ruled out as a cause of decline.

4. **Analyzing Bio Fertilizers**: The second option is bio fertilizers. These are microorganisms that enhance soil fertility. Similar to bio insecticides, bio fertilizers do not negatively impact reptiles and birds, so this option is also incorrect.

5. **Analyzing DDT**: The third option is DDT (Dichlorodiphenyltrichloroethane). DDT is a synthetic insecticide that has been widely used. It can runoff into water bodies and accumulate in aquatic organisms.

6. **Understanding Bioaccumulation and Biomagnification**: When fish consume DDT, it accumulates in their bodies. When birds and reptiles eat these fish, the DDT concentration increases in their bodies due to a process called biomagnification. This means that as you move up the food chain, the concentration of DDT becomes higher.

7. **Impact on Calcium Metabolism**: High levels of DDT disrupt calcium metabolism in birds and reptiles. This disruption leads to the thinning of eggshells, causing eggs to break prematurely, which directly contributes to the decline in their populations.

8. **Conclusion**: Based on the analysis, the correct answer to the question regarding the cause of the decline in the population of reptiles and birds is DDT.

### Final Answer:
The cause of the decline in the population of reptiles and birds is DDT (Dichlorodiphenyltrichloroethane).

---