Either Yasuomi is really curious about this new "species", which is understandable, or he's using Rie to find Himeno (he didn't expect Himeno to come see him herself earlier). His perspective about those cicadas makes me think the former is more probable.
Even if Himeno was bullied by most of her "soldiers", they're the only "friends" she have made so far. Other people go full megatherium for losing less friends than her.
Wonder if the mind control gimmick wears off if Himeno isn't around for long enough, which could make her mom's rescue pointless (if that's the case, even Rie might not know enough about this new wasp species to tell Himeno about it, or be sure about it -- it might still not matter for Himeno, actually trying to rescue a non-"brainwashed" mom would further cement the fact that Himeno does try to get along with other people, "soldiers" or not).
Finally, it's respectable that Himeno's caring enough about others to not have tried taking revenge on them.