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Have you been able to identify which kind of fruit fly it is? I assume in South FL it's the Caribbean fruit fly, not SWD or oriental, but it looks like the only solution is to bag the fruit before they ripen. I have never heard of correlations with sunny locations, maybe someone else knows more about that.
I have a friend with a very large loquat tree , in full sun and it gets infested. It’s around a lot of other fruit trees though, which may induce cross infestation. Is your neighbors tree isolated? Maybe it’s varietal resistance. I have a ruby quava that is always larva free but other varieties get infested. The same with some of my papayas.