He was just mentioned in passing when Rimuru was eating honey. I forgot which chapter tho, sry.
I found it! His first appearance is at chapter 30, when Rimuru just build his country after the fight with Orc Disaster. Though, it's just an appearance of a beetle and a bee, so non-novel readers wouldn't know about it. I think the name Zegion and Apito first appeared in slime diaries. I'm sure there's a chapter where they get bullied by Milim, I think?
Zegion and Apito appeared in chapter 77, right before he goes to Walpurgis. It was when he goes to the forest with the fairy girl to build bodies for her subordinates so that they can go to the meeting with her. Hope this helps!
Thanks you all for your replies i'm gonna check that ahah !<3
When did Zegion appeared in the manga ? I don't remember it at all... ;(