Last year a friend bought screened inner covers to help with summertime ventilation. When we checked his hives I spotted a small hive beetle running around on the wooden frame above the screen....ahaa!!! The black bug escaped the bees by fleeing through the screen.
I built me some screened inner covers but I used aluminimum window screen instead of hardware cloth. I put them under the telescoping covers with 1/4" wooden blocks to hold them up for the air to flow.
Sure enough...small hive beetles try to get inside by slipping under the tel cover and they can't figure out how to get in. And they are easy to squish (though I've never had a big beetle problem in my apiary). So we changed out the hardware cloth on his inner covers as a beetle control measure.
Fast forward to this year.... I introduced a swarm into the nuc bottom of my brand new Ulster Observation Hive. Rather than leave the windowed top out in the weather, I made a telescoping cover and (window) screened inner cover and put the box to the real SHB test. In the past I have been unable to keep bees in the back yard because of huge numbers of hive beetles coming from somewhere. Undeterred, I set up the nuc bottom out back with an AJ's Beetle Eater inside and the new inner cover. The first week's count:
40 SHB's squished on the inner cover screen
4 SHB's dead in the Beetle Eater
It sure will be easier to use the observation hive if I can just run out back to set it up for the next day. So far so good...in fact when I squished a SHB the other day, a bee grabbed a hold of it from below the screen and held on as I tried to get rid of it.