That's what I'd originally used that white slider board for; to check for mites after the OA dribble treatment. Never occurred to me it would chill them if I took it out permanently .. hopefully, the eggs and larvae survive and can warm up today.I use a screened bottom board over a solid bottom board all year. Under the screen is a slot for my inspection board. So I'm not using it as ventilation per se but more as a tool to look at hive trash/varroa drop. Just thought I'd mention it just in case you're considering removing it all together.