Ecological Indicators The presence of dragonflies can reveal changes in the water ecosystems more quickly than studying other animals or plants. In fact, from the nymph to the adult stage, the dragonfly has a significant, positive ecological impact. Dragonfly eggs are laid and hatched in or near water, so their lives impact both water and land ecosystems. Once hatched, dragonfly nymphs can breathe underwater which enables them to eat mosquito larvae, other aquatic insects and worms, and even small aquatic vertebrates like tadpoles and small fish and in the air. Adult dragonflies capture and eat adult mosquitoes. Community wide mosquito control programs that spray insecticides to kill adult mosquitoes also kill dragonflies.
The most effective stages in the life cycle of dragonfly that eradicate mosquitoes are-

Options

A. Larvae and Adult
B. Caterpillar and Adult
C. Nymph and Adult
D. Pupa and Adult

Explanation

To determine the most effective stages in the life cycle of dragonflies that help eradicate mosquitoes, we need to analyze the information provided about their life cycle and feeding habits.

### Step-by-Step Solution:

1. **Understanding Dragonfly Life Cycle**:
- Dragonflies undergo several stages in their life cycle: egg, nymph (larval stage), pupa, and adult.
- Each stage has different habitats and feeding behaviors.

2. **Identifying the Feeding Habits**:
- **Nymph Stage**: Dragonfly nymphs live in water and are known to eat mosquito larvae, other aquatic insects, worms, and small aquatic vertebrates like tadpoles and small fish. This indicates that they play a significant role in controlling mosquito populations in aquatic environments.
- **Adult Stage**: Adult dragonflies are aerial predators that capture and consume adult mosquitoes. This further contributes to the reduction of mosquito populations.

3. **Evaluating the Options**:
- **Option 1: Larvae and Adult**: This is incorrect because "larvae" is not a term used for dragonflies; they are referred to as nymphs.
- **Option 2: Caterpillar and Adult**: This is incorrect as caterpillars are the larval stage of butterflies and moths, not dragonflies.
- **Option 3: Nymph and Adult**: This is correct as both the nymphs and adults are effective in eradicating mosquitoes.
- **Option 4: Pupa and Adult**: This is incorrect because while adults are effective, the pupa stage does not feed and thus does not contribute to mosquito control.

4. **Conclusion**:
- The most effective stages in the life cycle of dragonflies that help eradicate mosquitoes are the **Nymph and Adult** stages.

### Final Answer:
The correct answer is **Option 3: Nymph and Adult**.