This is fantasy, not SF. It was a novel, alone in its own book, but it was a rather small book. And I read it in the 60's, I am sure. (I understand that the tag "fantasy" should not be used for a question to identify a fantasy story, only on questions on the genre itself)
It starts rather small scale, a girl (I think) who could control insects, bees if I remember properly, and uses them to pester another child (probably a boy) who has ways to get rid of the bees. Then it starts escalating.
In the end it becomes an epic fight between the forces of Good and those of Evil. I remember that the Zoroastrian deities Ahura Mazda and Ahriman are mentioned (I got this spelling in Wikipedia right now, the spelling in the book might well have been different but I am sure they were the ones from Zoroastrian religion)