If you want to leave Zoology and Entomology, then it seems like continued work focused on the fruit fly-- just because you’ve done it before- isn’t going to propel you forward.
Have you discussed your long term goals with any of these advisors to hear what they have to say about career prospects, advantages/disadvantages?
It all feels a little random to me. For most people by the time they apply for a doctorate program, they know they want to study with X professor (X can be 3 or 4 people in different institutions) researching Y topic with an end goal of Z. Are you there yet in your thinking?