Write what do phytophagous insects feed on.

Explanation

### Step-by-Step Solution:

1. **Definition of Phytophagous Insects**:
- Phytophagous insects are those that primarily feed on plants. The term "phytophagous" comes from the Greek words "phyto" meaning plant and "phagein" meaning to eat.

2. **Plant Parts Consumed**:
- These insects can feed on various parts of a plant, including:
- **Roots**: Some phytophagous insects target the roots of plants, extracting nutrients and damaging the plant's foundation.
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