Evidence: Farmers Burns and Dexter-Kemp are at their wits end. It has been a rough year farming
their crop of oranges. They have noticed an increase in insects climbing on their fruit. The veins on
the leaves are yellow and there is splotchy mottling all over the leaves. Some of the leaves are falling
off prematurely. After the fruit ripens, it starts to turn green.

What is the disease ?

Citrus greening disease

Explanation:

The symptoms sound like citrus greening disease. This disease is characterised by yellowing of the veins in the leaves, splotchy mottling of the entire leaf, leaves that fall off too early, and fruit that can turn green and tastes bitter.

Citrus greening disease is caused by a bacteria, and transferred by insects such as the Diaphorina citri.

the answer to your question is tooth decay.