The good thing about coconut trees is that they grow very fast and are cheap. Removal of a diseased tree is best, otherwise it will become a vector for other pests and infections. Pouring a gallon of poison, there by eliminating ever using the fruit, will also poison the ground water beneath it. Plant a resistant variety, remove a tree at any signs of the beetle or infection (or you will loose more) and enjoy the trees while they last.
Remember coconuts are not native to the Caribbean, so they will also suffer more disease and pest then native palms and can pass sickness to the native species. The only animals benefiting from the coconut food growing on these shores are humans and some beetles that carry a virus. We on average loose five trees a year due to storms or disease, replant ten and cut down ones we don't like how they turned out. Keeps things interesting.
Here's the hubby ( Capt. Coconut) replanting with our potlicker.