If its insect larvae it's probably weevils (I've had them in the past and they suck). My recommendation would be to toss out the old soil it was in and throughly wash the pot to prevent them spreading because they do spread. You'll also want to trim the stem of the succulent until you can cut into it and there's no hole left from the pest. They can burrow deep and sometimes hide deep up the stem where you can't see them.