Blowing the deceased
insecta species back the way they came is vastly easier than blowing them through the screen that caught them, so you will want to
work from below. If you have compressed air, this is the time to use it. Using
water from below is likely to be messy. But then, those screens are advertised as easy to mount, so they should be easy to dismount and wash.
Which way does your air flow? If you can arrange to
exhaust rather than suck into the
cabin, fewer bugs will sacrifice themselves on the screens.