Which of the following arthropods are harmful?
(a) Culex
(b) apis
(c) Bombyx
(d) Locusta

Options

A. a and b
B. b and c
C. b and d
D. a and d

Explanation

To determine which arthropods from the given options are harmful, we will analyze each option based on their effects on humans and the environment.

### Step-by-Step Solution:

1. **Analyze Culex:**
- Culex is a genus of mosquitoes.
- They are known vectors for various diseases, including filariasis.
- **Conclusion:** Culex is harmful to humans as it can transmit diseases.

2. **Analyze Apis:**
- Apis refers to honey bees, specifically Apis indica in this context.
- Honey bees are primarily known for producing honey.
- While they can sting, they are not generally considered harmful and are economically important.
- **Conclusion:** Apis is not harmful.

3. **Analyze Bombyx:**
- Bombyx mori is the scientific name for the silkworm.
- Silkworms are cultivated for silk production and do not pose any harm to humans.
- **Conclusion:** Bombyx is not harmful.

4. **Analyze Locusta:**
- Locusta refers to locusts, which are a type of grasshopper.
- Locusts can be agricultural pests that cause significant damage to crops, leading to economic loss.
- **Conclusion:** Locusta is harmful as it negatively impacts agriculture.

### Final Answer:
The harmful arthropods from the options provided are:
- (a) Culex
- (d) Locusta