Two Decades of Varroa, Part II

Bee Culture (November) Vol. 135 (11): 19-21




Dr. Malcolm T. Sanford


Last month I discussed the arrival of the Varroa mite (Varroa destructor) and the seminal decisions made by beekeepers and regulators, which abandoned regulatory efforts and steered beekeepers toward dependence on what has been termed the “pesticide treadmill”.  The first approved pesticide (fluvalinate, brand name Apistan®) would help beekeepers weather the first decade of the Varroa experience in the U.S.  But this “silver bullet” and others of its ilk could only be relied on temporarily as the chemicals and mites engaged in a war of effectiveness.


A problem with Varroa was that it was so devastating to honey bee populations.  Beekeepers observed the effects of the mite on the wild or feral populations left to their own devices.  Over 90 percent died (collapsed), depleting the landscape of this heretofore ubiquitous insect, something that commercial beekeepers could not tolerate and stay in business.  Thus, beekeepers became paranoid about treating their bees in an effort to rid them entirely of mites, more often than not treating due to the presence of a single mite.  Because the first treatment material, the pyrethroid fluvalinate, formulated as Apistan®, was so effective, killing well over 90 percent of the mites in a colony, this appeared to be a definitive answer to mite control.  But in the end this only accelerated the development of resistance by Varroa to the treatment.  In addition, there were rumors of increasingly use of “extra-legal” applications that worried many in the regulatory and research community.


In April, 1992, I wrote: “The rest of the United States is starting to realize what many beekeepers in Florida have learned in the last two years.  Varroa mites are here to stay and monitoring the mite population is the best way to keep parasite populations low.  Dr. Eric Mussen in his January/February 1992 issue of From the UC Apiaries published a piece called ‘Varroa Getting Nasty.’  It seems many beekeepers in California got a surprise when their colonies collapsed last fall.  The symptoms at first seemed to be classical for tracheal mites: 1. rapid loss of adults; 2. tiny clusters of bees with a queen; and 3. abundance of stored honey and pollen.  Not characteristic was varying amounts of capped brood.  The latter revealed that something else was going on; the adults were not being replaced.  Developing pupae were killed in their capped cells by mites and never emerged.

“To prevent colony collapse, Dr. Mussen suggests checking bees for Varroa two to four times per year. Finding a mite or two doesn't mean the colony is in immediate jeopardy, but it will require treatment sooner or later. And if another check, not too much later, turns up a lot of mites, then you are the unlucky recipient of someone else's failure to detect a problem. Choose your method of colony examination (ether roll, tobacco smoke, Apistan®), he concludes, early detection is critical to colony protection.

“ ‘Looking for trouble,’ is the way Dr. Roger Morse categorized the perpetual hunt for Varroa in the April, 1992 issue of Bee Culture.  He concluded, ‘ all probability every beekeeper in the continental U.S. and Canada will have infested hives within two to four years.’  He recommends, therefore, that beekeepers in the U.S., Canada and Mexico check colonies for Varroa at least twice a year.  Although it has been reported that colonies sometimes take years to die after being infested with Varroa, there are exceptions. Dr. Morse speaks of a New York beekeeper whose hives produced over 100 pounds of honey in July and August, yet were dead by late fall.  And Dr. Mussen describes a California beekeeper, who after a good producing season, saw 75 percent of his colonies severely damaged or dead by Christmas.  That beekeeper is no longer in business and had to sell out at submarket prices.  These cases may be because of drift by bees from nearby heavily infested apiaries that were not treated.  Also the fact that mites are hidden and protected in capped brood cells may mean a serious undercount in those found on adults or in bottom board debris.

“Fortunately, detecting Varroa is a fairly simple process. A number of methods are described by Dr. Morse, including: examining brood or adults; sorting through bottom board debris; and using the ether roll.  The technology to determine when a Varroa infestation reaches a treatable level by any detection method currently in use has not been well worked out.  Detection results may vary and are dependent on bee/mite population dynamics.  For example, in the fall, Dr. Morse says, with little or no brood, you are more likely to find mites on adults, whereas in the spring they will be easier to find in brood.  Practical experience by the Florida Division of Plant Industry indicates that when 20 mites in an ether roll of approximately 300 adult bees are found, a colony should be treated with Apistan®.  However, Dr. Harvey Cromroy of the EntomologyNematology faculty, University of Florida, believes more than five mites is a treatable level.  Dr. Morse concludes finding 30 to 40 mites per hundred bees (ether roll) is serious and the colony may be beyond saving.  The ability to correlate ether roll with other detection methods is not presently available.” 1  This lack of a suitable treatment threshold has confused the Varroa control issue considerably, and to some extent this still exists today. 

Since that time, other detection methods have been implemented beyond the ether roll, which had the disadvantage of killing bees and using smoke from materials like citrus leaves that disrupted the colony’s organization.  I stated in an earlier column in this series that Dr. William Ramirez of Costa Rica had suggested powder be used as a control as far back as November, 1987.  This concept is now being employed using powdered sugar pioneered by Dr. Kamran F. Fakhimzadeh, of U. Helsinki in Finland2 and the University of Nebraska.3  In addition, many kinds of monitoring boards have been developed that can be inserted into beehives, often with greased surfaces to trap fallen mites and not allow them to return to their host bees.  These also employ a screen (8 mesh to the inch), which allow the mites to fall through, but keep the bees from contacting the monitoring device (sticky board) on the bottom board.  These screened bottom boards are now in widespread use and beekeepers have often found them advantageous in their own right, eliminating moisture from a colony ensuring better winter survival.

Drone brood is preferred by Varroa.  It has a longer post-capping period and so a female mite infesting a developing drone can potentially produce more offspring.  Drone brood is also the only caste affected by Varroa in the original host, the Eastern honey bee (Apis cerana).  The mite is so devastating on the western honey bee (Apis mellifera) precisely because it infests both drone and worker brood.  Drone brood management, therefore, can be used effectively to detect as well as control mites.  Trapping mites in drone brood and then removing them before emergence has become an excellent strategy, especially in developing countries where pesticides are often not an option.  Dr. Zachary Wang at Michigan State University has developed what he calls a Mite Zapper®, which also targets drones.

Pesticides, so-called “hard” applications, have become the treatment of choice when available, especially in large-scale operations where time and labor expended on Varroa control needed to be kept to a minimum.  Beekeepers got a good decade of effectiveness from the pyrethroid, fluvalinate, originally applied via wood strips, but later in plastic strips, formulated as Apistan®.  However, for many it has now lost its effectiveness.  The next chemical to come along was the more highly toxic and problematic organosphosphate, coumaphos, formulated on plastic strips as CheckMite+®.  Beekeepers are only beginning to experience dealing with this material and already it shows signs of mite resistance.  A third material, amitraz, representing a different class of pesticides, was employed for short period as the labeled material, Miticure®, formulated on plastic strips, but was withdrawn from the market by the manufacturer as too problematic.  The fact that amitraz resistance by Varroa mites exists, however, suggests that it has often been used in “extra legal” formulations.

Hard pesticides like fluvalinate and coumpahos were relatively flexible molecules that worked across a wide range of temperature and other variables.  This allowed beekeepers to rely totally on them to manage mite populations.  With elimination of these materials through Varroa resistance fostered by continuous use, beekeepers have had to become much smarter in mite control by using less-toxic, more so called “soft” materials.  These include organic acids (formic and oxalic) and essential (thymol, wintergreen) and other (food-grade mineral) oils.  These materials were much less forgiving and more or less effective based on environmental circumstances in the bee hive.  However, the potential of them impacting the honey crop through contamination was less because many are found naturally in honey.

As beekeepers have lost effective materials due to resistance, they have resorted to a technology called Integrated Pest Management or IPM.  Although often viewed as not employing chemical treatments at all, IPM is really about managing pesticide use to minimize contamination and the development of resistance.  Its touch stone is the idea that beekeepers should not use pesticides to totally rid bees of mites (eradication philosophy), but to maintain a low non-damaging level of Varroa in their colonies.  This is done using a number of technologies, including hard pesticides, soft chemicals (organic acids and oils, and biomechanical tools (screened bottom boards, powdered sugar dust, drone trapping).

Varroa is here to stay.  This conclusion may seem obvious, but cannot be stated too many times in the modern U.S. beekeeping climate.  My friend Martín Braunstein, an Argentine queen breeder, has even suggested it be referred to as the fourth individual in the colony after the queen, worker and drone.4   Given this circumstance, the long-term solution to Varroa mite control must be looked at in terms of innate tolerance or resistance through genetic management.  Fortunately, there are indications that the European honey bee (Apis mellifera) itself can implement this technology, just as has its cousin the Asian honeybee (Apis cerana).  Two outstanding examples of this have been documented. 

The Africanized honey bee is a New World example of this phenomenon.  Varroa mites were introduced via Japan in the 1970s into Paraguay and quickly spread to much of Latin America.  Mite tolerance or resistance by Apis mellifera is most documented in Brazil.  The Africanized honey bee in this sleeping giant has metamorphosed from a beekeeping industry pariah to savior.5  Varroa is ubiquitous in Brazil, but no treatments of any kind are used by beekeepers.  Clearly, the Africanized honey bee infested with Varroa cannot produce the prodigious amounts of honey per colony that true European honey bees do, but this is made up for by the sheer number of feral colonies found in the wild.  In addition, Brazilian beekeepers have to do minimal management when compared to that required by Varroa-infested bees in much of the rest of the world.

The other example, more recently come to light, is South Africa.  Relatively recently infested with Varroa (1997), I wrote the following in my report of the Apimondia meeting in Durban, South Africa in  2001: “It will be instructive for the rest of the world to closely follow the Varroa situation in south and central Africa.  This situation not only has great importance for beekeeping, however.  The honey bee is a native insect in Africa and therefore its survival and health is important for many wild plant communities that rely on it for pollination and propagation.”6  The jury is in with a report in the 40th  Apimondia conference in Melbourne, Australia just concluded.  “The rapid development of mite tolerance in South African honeybees is thought to be due to the well developed removal of Varroa-infested brood and the short post-capping period of worker brood, particularly Cape honeybees.  Together these resulted in a very rapid increase in infertile mites in the colony, the collapse of the mite population, and Varroa tolerance.”  Tellingly, it was concluded: “A ‘live and let die’ approach to the wild and commercial honeybee populations was crucial to the development of population-wide Varroa tolerance.”7

There is more and more evidence that Varroa tolerance already exists at least in rudimentary ways in European honey bees in the U.S..  The introduction of Russian honey bees, as well as breeding bees for hygienic behavior in general and Varroa in particular, is quite promising.8

All the above evidence is encouraging in the sense that the Varroa situation has indeed stabilized itself and is now moving into a different phase in U.S. beekeeping.  Thus, beekeepers now have rational and powerful tools to manage mite populations in colonies and the long-term solution provided by nature, genetic selection, is on the verge of becoming a reality.  Given these circumstances, I am more encouraged than ever that beekeeping in the U.S. has a brighter future than many might have thought a few short years ago.  Many of the challenges Varroa has wrought in the twenty years since its introduction still exist, but it is more and more probable that my statements written in a recent Bee Culture column might be apt when I said that I didn’t want to be forced into being a pest control operator. Thus, it may not be as protracted as I thought when I concluded: “I’ve waited a long time to resume my beekeeping activities.”9: “.



  1. Sanford, M.T.  Apis Newsletter, Volume 10, Number 4 (April 1993),, accessed August 14, 2007.
  2. Fakhimzadeh, Kamran.  Detection of major mite pests of Apis mellifera and development of non-chemical control of varroasis.  Department of Applied Biology, University of Helsinki, Finland,.accessed August 14, 2007.
  3. Ellis, Marion, Bee Tidings, University of Nebraska, January 2000., accessed August 14, 2007.
  4. Sanford, M.T. 2007 "The Fourth Individual in a Honey Bee Colony," Bee Culture (September) Vol. 134 (9):  17-19.
  5. Sanford, M.T. 2005. "Beekeeping in Brazil: A Slumbering Giant Awakens," American Bee Journal Vols. 144-145 (four installments: September and December 2004; January and March 2005).
  6. Sanford, M.T. 2002 "Apimondia in South Africa," Bee Culture, Vol. 130 (seven installments: January, February, March, May, July, August, September).
  7. Allsop, M.  2007  Varroa Tolerance in South African Honeybees, Proceedings of the 40th Apimondia International Apicultural Congress, Abstract No. 91.
  8. Sanford, M.T. 2004. "Mite Tolerance in Honey Bees," Bee Culture (October) Vol. 132 (10): 23-26.
  9. Sanford, M.T. 2005. "Survivor Bees Around The World; Why I No Longer Keep Bees," Bee Culture (August) Vol. 133 (8): 19-21.