June bug vs June beetle

June bug and June beetle both are nouns.

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

As nouns, June bug and June beetle are synonyms defined as:

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

Other synonyms of June bug include May beetle, May bug.

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