mirid bug vs plant bug

mirid bug and plant bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
mirid bug	Yes	No	No	No
plant bug	Yes	No	No	No

As nouns, plant bug is a hypernym of mirid bug; that is, plant bug is a word with a broader meaning than mirid bug:

Other hypernyms of mirid bug include leaf bug.

mirid bug (noun)	plant bug (noun)
a variety of leaf bug	small bright-colored insect that feeds on plant juices