A natural way to control those pesky Varroa is with Drone Foundation. Varroa prefer to deposit their eggs on drone comb. By inserting a piece of Drone Foundation into your brood nest, you can lure Varroa Mites to the developing drone brood. Eleven days after the egg has been laid, the bees will cap the cells. You should remove the comb before the bees emerge in approx. 21 days. Put the comb in the freezer for a few days and it will kill the brood and the mites. Then scrape the caps off with a cappings scratcher and return it to the hive. The bees will clean it up, drag the dead out and refill the comb, starting the cycle over again. Measures 8-1/2" and sold in 10 sheet packs only.
I purchased this foundation for the purposed of IPM without chemicals. The foundation arrived with no vertical wire supports. After installing the foundation into frames with double horizontal cross wiring, the foundation did not remain in place in the frame. This sagging and folding of the wax foundation occurred both in the hive and while in storage.
I do not recommend this product as currently offered. I believe if vertical crimped wiring is added to the foundation I believe it would ideally serve its purpose.