A microbial biocontrol agent that can be used to control butterfly caterpillars is

Options

A. Trichoderma polysporum
B. Bacillus thuringiensis
C. Streptococcus
D. mycorrhiza

Explanation

To solve the question regarding which microbial biocontrol agent can be used to control butterfly caterpillars, we will analyze the given options step by step.

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are:
- Trichoderma polysperma
- Bacillus thuringiensis
- Streptococcus
- Mycorrhiza

2. **Evaluate Trichoderma polysperma**:
- Trichoderma polysperma is a fungus that primarily releases a chemical called cyclosporine A, which acts as an immunosuppressive agent. It is not known for controlling insect pests, including butterfly caterpillars.

**Hint**: Look for the primary function of each organism to determine its relevance to pest control.

3. **Evaluate Bacillus thuringiensis**:
- Bacillus thuringiensis (Bt) is a gram-positive bacterium that acts as a biocontrol agent against various insect pests. It produces an endotoxin that is toxic to the gut of insect larvae, including caterpillars. When these larvae ingest the bacterium, the endotoxin disrupts their gut, leading to their death. It is commonly used in agriculture as a natural pesticide.

**Hint**: Consider whether the organism is known for its insecticidal properties.

4. **Evaluate Streptococcus**:
- Streptococcus is a genus of bacteria that primarily produces enzymes like streptokinase, which is involved in blood clotting. It does not have any known application in controlling insect pests.

**Hint**: Determine if the organism has any relation to pest control or agriculture.

5. **Evaluate Mycorrhiza**:
- Mycorrhiza refers to the symbiotic association between fungi and higher plants. While beneficial for plant health and nutrient uptake, it does not serve as a biocontrol agent for insects.

**Hint**: Assess whether the organism has a symbiotic or mutualistic role that relates to pest management.

6. **Conclusion**: After evaluating all the options, it is clear that the correct answer is **Bacillus thuringiensis**, as it is specifically recognized for its effectiveness as a biocontrol agent against butterfly caterpillars and other insect pests.

### Final Answer:
The microbial biocontrol agent that can be used to control butterfly caterpillars is **Bacillus thuringiensis**.