green June beetle vs June bug

green June beetle and June bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
green June beetle	Yes	No	No	No
June bug	Yes	No	No	No

As nouns, June bug is a hypernym of green June beetle; that is, June bug is a word with a broader meaning than green June beetle:

green June beetle: large greenish June beetle of southern United States
June bug: any of various large usually brown North American leaf-eating beetles common in late spring; the larvae feed on roots of grasses etc.

Other hypernyms of green June beetle include June beetle, May beetle, May bug.

green June beetle (noun)	June bug (noun)
large greenish June beetle of southern United States	any of various large usually brown North American leaf-eating beetles common in late spring; the larvae feed on roots of grasses etc.