Not to sure what you mean by: "leaf hoppers" but, I have found that in my garden, the most beneficial insect to add was the Ladybug.
Make a solution of sugar and water up and spray the insects (ladybugs) with it, then spray the infected plants and dump the ladybugs over the infected plants and let them do their thing. They are voracious eaters.
I do know that people usually use ladybugs for aphids but, I put a couple of bags of them on my vegetable garden last summer and they worked like a charm.
