mealybug vs mealy bug

mealybug and mealy bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
mealybug	Yes	No	No	No
mealy bug	Yes	No	No	No

As nouns, mealybug and mealy bug are synonyms defined as:

mealybug and mealy bug: scalelike plant-eating insect coated with a powdery waxy secretion; destructive especially of fruit trees

mealybug (noun)	mealy bug (noun)
scalelike plant-eating insect coated with a powdery waxy secretion; destructive especially of fruit trees	scalelike plant-eating insect coated with a powdery waxy secretion; destructive especially of fruit trees