There might be literally millions of insects in a field, how many lasers would you need for that? Also, you would need much more precise sensors as detecting an insect is way harder than a bird. Such system would be way too expensive, unless you'd like to pay 100 euros for a loaf of bread.

Bill Gates is funding some efforts to that effect to kill mosquitos.

https://www.ted.com/talks/nathan_myhrvold_could_this_laser_z...

But some are good to have around, that's the whole problem...

We can use deep learning for that :)