Give an example of biological weed control.

Explanation

### Step-by-Step Solution:

1. **Understanding Weeds**:
- Weeds are unwanted plants that grow alongside crops in agricultural fields. They compete with crops for essential resources such as nutrients, water, and sunlight, which can negatively affect crop health and yield.

2. **Importance of Weed Control**:
- Effective weed control is crucial for maintaining the health of crops. Weeds can hinder growth and reduce the overall productivity of agricultural lands.

3. **Traditional Weed Control Methods**:
- One common method for controlling weeds is the use of herbicides (chemical weed killers). However, these chemicals can have harmful effects on the environment and may also affect the crops themselves.

4. **Biological Weed Control**:
- An alternative to chemical herbicides is biological weed control, which involves using living organisms to manage weed populations. This method is more environmentally friendly and sustainable.

5. **Example of Biological Weed Control**:
- A specific example of biological weed control is the use of certain insects that target specific weeds. For instance, the use of *Collyria* insects to control the weed *Opuntia* (commonly known as prickly pear) is a notable example. These insects feed on the sap of the *Opuntia*, effectively reducing its population and impact on crops.

6. **Conclusion**:
- Biological weed control is a viable and environmentally friendly method to manage weed populations, and using specific insects like *Collyria* to target weeds such as *Opuntia* illustrates this approach effectively.