Devils first appeared in the MM1 (vs. demons who were introduced in Eldritch Wizardry), so they should have been designed by Gary, per the info from the Preface.
I don't recall Gary otherwise talking about his devilish inspirations, but they surely included Dante and Milton, at least indirectly.
https://en.wikipedia.org/wiki/The_Deadly_Mantis
I think I found a possible origin - 1957 creature feature
giant mantis thawed from a glacier and attacks towns
@grodog do you happen to know the source material for our insectoid friend?
I have no idea!