Correct Option: B. Mealybug Detailed Explanation: Swollen shoot disease of cocoa is a viral disease that significantly affects cocoa plants, leading to reduced yield and quality of cocoa beans. The disease is primarily transmitted by specific insect vectors, and in this case, the correct answer is the Mealybug.

1. Understanding the Disease:
2. Swollen shoot disease is caused by the Cocoa swollen shoot virus (CSSV). The symptoms include swelling of the stems, leaf distortion, and ultimately, the death of the plant. This disease can devastate cocoa plantations if not managed properly.
3. Role of Insects in Transmission:
4. Insects play a crucial role in the transmission of many plant viruses. They can carry the virus from infected plants to healthy ones as they feed on the sap of the plants.
5. Why Mealybug is Correct:
6. Mealybugs are known vectors of the Cocoa swollen shoot virus. They feed on the phloem sap of cocoa plants and can transmit the virus when they move from an infected plant to a healthy one. Their feeding habits and life cycle make them effective carriers of the virus.
7. Mealybugs are small, soft-bodied insects that often appear as white, cottony masses on the stems and leaves of plants. Their presence is often a sign of viral infection in cocoa.

Why the Other Options are Incorrect:

• A. Steam Borer:
• The steam borer is a pest that primarily affects the cocoa tree by boring into the stems and pods, causing physical damage. However, it does not transmit swollen shoot disease. Its role is more about causing structural damage rather than viral transmission.
• C. White Fly:
• Whiteflies are known to transmit other plant viruses, but they are not the primary vectors for the Cocoa swollen shoot virus. While they can cause stress to the plant and may be involved in other diseases, they do not have a significant role in the transmission of swollen shoot disease.
• D. Scale Insect:
• Scale insects can also affect cocoa plants by feeding on sap and causing stress, but like whiteflies, they are not known to transmit the Cocoa swollen shoot virus. Their impact is more related to plant health rather than viral transmission.

Summary of Key Points:

• Correct Answer: B. Mealybug is the primary vector for swollen shoot disease in cocoa.
• Disease Impact: Swollen shoot disease leads to severe yield loss and plant death.
• Insect Transmission: Mealybugs feed on cocoa sap and effectively transmit the virus.
• Other Insects: Steam borers, whiteflies, and scale insects do not transmit swollen shoot disease.

This understanding is crucial for effective management and control of swollen shoot disease in cocoa cultivation.