medfly vs fruit fly

medfly and fruit fly both are nouns.

Word	Noun	Adjective	Verb	Adverb
medfly	Yes	No	No	No
fruit fly	Yes	No	No	No

As nouns, fruit fly is a hypernym of medfly; that is, fruit fly is a word with a broader meaning than medfly:

medfly: small black-and-white fly that damages citrus and other fruits by implanting eggs that hatch inside the fruit
fruit fly: any of numerous small insects whose larvae feed on fruits

Other hypernyms of medfly include pomace fly.

medfly (noun)	fruit fly (noun)
small black-and-white fly that damages citrus and other fruits by implanting eggs that hatch inside the fruit	any of numerous small insects whose larvae feed on fruits