Which is not ecomically useful

Options

A. Apis dorsata
B. Lac insect
C. Bombyx mori
D. Lepisma.

Answer

To determine which organism is not economically useful among the given options, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Identify the First Option: Apis dorsata**
- Apis dorsata is commonly known as the giant honeybee. It is economically useful because it is involved in apiculture, which is the practice of keeping bees for honey and wax production. Therefore, this option is economically useful.

2. **Identify the Second Option: Lichen insect**
- The lichen insect is important in lac culture. Lac is a natural resin that is harvested from the secretions of these insects and is used to produce dyes and in various industries, including textiles. Hence, this option is also economically useful.

3. **Identify the Third Option: Bombix mori**
- Bombix mori, or the silkworm, is crucial in sericulture, which is the cultivation of silkworms for silk production. This makes Bombix mori economically valuable as it contributes significantly to the silk industry.

4. **Identify the Fourth Option: Lepisma**
- Lepisma, also known as silverfish, is an insect that is not known for any significant economic usefulness. It is often considered a pest and does not contribute to any major industries or economic activities.

### Conclusion:
Based on the analysis, the organism that is not economically useful is **Lepisma**.

### Final Answer:
**Lepisma**

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