Well, "ζουζούνι" is an onomatopoeic word, because insects sound like "ζουν ζουν" when they're flying!
Bees. And other pollinators. Honey. Fruit. Ladybugs kill aphids. Dragonflies and preying mantises also kill other pesky insects.
Ζουζούνι = bug; the word is used in informal contexts the way bug is used informally in English. (There is a formal definition of bugs as a very specific group of insects - these are the "true bugs" in English.)
Έντομο = insect; a clear zoological classification is implied here, but the word can be used in both formal and informal situations.