HI Jerry. I did some research on your question and find no definite answer to it. Some sites say the glue used to make plywood may emit gases over time but also says there's no research on whether the bees tendency to coat the inside of the hive with propolis reduces that or not.
Personally I don't think non pressure treated plywood is a big contributing factor to the loss of bees. I believe it is a combination of factors such as how healthy the bees are, how much stress they are under and how healthy the environment they forage is.
I wouldn't use plywood to build a hive myself. Cypress, cedar, beech and oak woods would be much better and last longer.
Also, honey bees won't live in anything that is seriously hazardous to them. They seal all cracks no matter how tiny we think they are with propolis which guards against viruses and bacteria. Some studies have shown thaty even use propolis to seal off unsafe honey in the hive.
