Best gun for shooting cicadas with the least amount of physical damage?

Hi. New here.

I study cicadas (I grew up calling them locusts). Generally I collect them with a net, with a light trap at night or by capturing them as nymphs. I'd like to know what those familiar with air rifles would suggest for stunning or killing these generally large insects at distances of 30-60 ft with the least amount of damage. I've been practicing with a Crosman P1377 hand pump pistol and a green Truglo dot sight on a Clevercraft scope mount. The setup seems pretty accurate and I'm sure it would be with more practice or a more experienced shooter. I've been using blunt face pellets at three pumps, which I've read is about 350fps.... but am open to trying a different setup if the consensus is I should. 

Thank you for taking the time to read this and special thanks to anyone who takes the time to respond.
 
A regular airgun is going to turn them to goo, even at only 350 fps; forget it.

If you want to study them, your best bet is catching them in a net, as you've been doing all along. Maybe draw them in with a bug zapper light, but with the fences de-energized and have a net waiting for them?

Also, being out at night looking for them coming out of the ground will be a good strategy.