He kept the smoke inside for 60 seconds, then removed the bees. It gave us the idea to start looking at other plants that, when burned, give off chemicals that removed the mites without harming bees. Among the 40 different plants Eischen has tested, the most promising plants are creosote bush and dried grapefruit leaves. Creosote bush smoke achieves a 90 to 100 percent mite knockdown after 1 minute, but Eischen says that excessive exposure can harm the bees. It's hard to find chemicals that remove mites without harming bees.
Grapefruit leaves fit that description.
After 30 seconds, smoke from the grapefruit leaves knocked down 90 to 95 percent of the mites in the cage test. With grapefruit leaves, however, few of the mites are killed. Most simply fall off the bees. The smoke chemicals either irritate the mites or confuse them. But we do know that the grapefruit leaf smoke doesn't seem to have any bad effects on the bees at all.