fruit fly vs medfly

fruit fly and medfly both are nouns.

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

As nouns, medfly is a hyponym of fruit fly; that is, medfly is a word with a more specific, narrower meaning than fruit fly:

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

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