Insatiable is not applying to Mutation Stacks gained through Larva. I have 374% chance for an additional Mutation Stack but I only gain the default 1/5 through Larva, I have tested it in both missions and Simulacrum.
Nothing in its wording implies Larva shouldn't be affected by the mod.
Much like how, in the past, you weren't able to get Mutation Stacks if you infused an ability over Virulence which made you lose your passive completely. I did a bug report on that back then and it was changed, so I feel like this is in line with the same idea.
Larva gains stacks, it should be affected just like Virulence. Not only does it make sense but it also allows for more build diversity.
