Serious scientists use a organic Malaise trap. Rene Malaise invented it in 1934.
It is a "flight intercept" insect trap.
The trap is essentially a portable dining fly with open sides and screened front and back, a screen hanging in the center, and a peaked roof at one end. The bugs fly into the enclosure, hit the middle netting, and fly up to get out. As they follow the peak seam at the top, it leads to a collection device at the top.
The insect trap is checked about weekly and primarily collects flies and wasps, although many other insects find their way to the collection point as well.
The professional bug collectors use an agent in the collection device to stun or knock out the insects, then they fall into alcohol or onto a strip. This leaves the insects in a condition in which comparison of insect populations is easy.
For insects that fall when they hit the center wall, some naturalists put a collecting pan on the ground against the wall with a preservative to retain the insect.
Why not build one in your backyard?