ether roll levels. Return the bees back to their colony. If the numbers are at or above the economic threshold, you should treat your colony. If the numbers are below then you can wait. Overnight sticky sheets can also be executed with little effort. Various beekeeping equipment vendors sell sticky sheets. Place these into your colony and the next day (18-24 hours) remove them and count the number of mites. It’s best to keep screens in the colonies for 3 days, count mites, and calculate an average mites per day. If the mite number exceeds those above it is time to treat.
Cultural methods for Varroa mite control include using drone comb or bottom screens to trap Varroa mites. Varroa mites prefer drone brood. Using a few frames of drone comb per colony draws mites into the cells which are then capped by the worker bees, trapping the mites within. The frames are removed and put into the freezer 24-48 hours to kill the mites.
Bottom screens are also an effective control method. They are basically a wood-bound screen (8-mesh hardware cloth) that is placed underneath the brood chamber. The mites fall through the screen onto the bottom board or ground. The mites are thus separated from the bees and eventually die. It should be stressed that these two treatments alone will not rid your colonies of all Varroa mites and should be used as a means to delay the economic threshold and the need for a chemical application. Hopefully in the future, genetic bee stocks resistant to Varroa mites will become more available to beekeepers.
Tracheal Mites (Acarapis woodi):
Tracheal mites were first detected in the United States in 1984 and have since caused the loss of tens of thousands of colonies and millions of dollars. Tracheal mites infest the tracheal system of the adult honey bee. Levels are highest during the winter and spring. Mites prefer adult bees less than four days old. Once they are on the bee, mites are attracted to carbon dioxide emissions and enter the spiracles located on the thorax which lead to the tracheal system. They puncture the wall of the trachea and suck the hemolymph of the bee. Tracheal mites live, breed and lay eggs in the tracheal system. The adults and eggs plug the tubes of the trachea which impairs oxygen exchange. They also spread secondary diseases and pathogens since they puncture the trachea in order to feed. Individual bees die due to the disruption to respiration, damage to the tracheae, microorganisms entering the hemolymph, and from the loss of hemolymph. Honey production may be reduced when over 30 percent of the population is infested with tracheal mites. Also, the likelihood of winter survival decreases with increasing infestation of the mite. Mites are transmitted from bee to bee within a colony and to other colonies by robbing or drifting bees.
Infested bees will be seen leaving the colony and crawling on the grass just outside the hive. They will crawl up the blades of grass or the hive, fall back down and try again. The wings may be disjointed and the bees unable to fly. The abdomens may be swollen. In late stages of infestation, bees will abscond from the hive. If you are unsure if you have tracheal mites, send a sample of bees in alcohol to your local county extension agent for verification.