aphid vs plant louse

aphid and plant louse both are nouns.

Word	Noun	Adjective	Verb	Adverb
aphid	Yes	No	No	No
plant louse	Yes	No	No	No

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

aphid: any of various small plant-sucking insects
plant louse: any of several small insects especially aphids that feed by sucking the juices from plants

Other hypernyms of aphid include louse.

aphid (noun)	plant louse (noun)
any of various small plant-sucking insects	any of several small insects especially aphids that feed by sucking the juices from plants