First, I guess you'll have to downsize a bit. Elephants are classed as being to big for the spell to work, so you'll have to go with something like horses.
Second: is the range/area of 30 feet in reference to how close they have to be to you, as well as the aoe?
Rules as written, it affects an unlimited number of willing creatures within a 30 foot AoE of you.
But it has a duration of 24 hours, and you can continually retrigger it as many times as you want during that time by expending a standard action. I could see an argument being made to ready an action to transform the bugs when they come into range as they dive bomb the opponent, but even if that works, the caster is going to be awfully close to ground zero.
As far as I can tell this would work actually. I can't see anything in the rules text that says it wouldn't. The creatures would certainly die on impact (excess damage in this case will carry over to their normal form's HP pool) but they were fine being summoned into battle to possibly die anyway so I don't see what changes, they'd probably still be considered willing considering they are summoned creatures under control of the caster. And the spell states they retain the transmuted form for the duration (24h) or until dropped to zero hit points, and does not state the creatures would revert when leaving the spell area.
Well fuck me. I don't want that to work, but I think it does. I can't argue a reason it wouldn't. Have fun carpet bombing your enemies with horses, I guess.