VSH/ POL–LINE BEES
CAN WE ACHIEVE REAL VARROA MITE RESISTANCE IN OUR LIFETIMES?
Published in BEE CULTURE September 2019
As a commercial beekeeper, I have to admit I was skeptical when news of resistant hygienic response to Varroa mites broke almost 20 years ago. After all, synthetic treatments worked, and thoughts of the degree of controlled breeding required to isolate and maintain the desired traits would be difficult to achieve. Non-hygienic drones from nearby beekeepers would dilute the traits, and treatments would always be required. Though we included hygienic breeders early in our queen rearing program, we performed little back checking to verify the presence of hygienic traits.
At the same time, we decided to limit the number of treatments to one synthetic and one organic treatment per year. While we have been able to maintain this limited treatment regimen for close to 20 years, we have learned that many beekeepers are resorting to multiple synthetic treatments per year to achieve control.
In March of 2018 we invited Adam Finkelstein of VP Queen Bees to sift and select potential queen breeder stock from a random bee yard near Bunkie, LA. I was surprised how quickly he was able to find some queens with low enough mite counts in their populations to mark for future checking. Regardless of whether they made the cut later on I was impressed with their low mite counts over 8 months after their last treatment. In April of 2018 we set up an experiment to mimic the natural free-fall or carry-out of mites from feral colonies in trees or buildings with completely open bottoms on pallets. Again, when we checked mite counts for the 27 colonies chosen at random during set-up and again we were surprised to find several colonies with very low mite counts. I began to consider how we had conducted our queen rearing program so I decided to revisit the origins of our experience with the VSH program and the science which led to its development.
The hygienic response of honeybees to diseases and pests was explored as early as 1935 by Dr. Otto Park an Associate Professor at the Iowa Agricultural Experiment Station when the honey bee industry was in the grip of an American Foulbrood (AFB) epidemic. At a time when the sole remedies for AFB were shaking bees out of infected colonies and burning the hives, he proposed a genetic solution similar to the apparent success of other agricultural genetic solutions to diseases and pests at that time (Park, 1936).
In the late 1950’s and early 1960’s, a student of O. W. Park, Dr. Walter Rothenbuhler at Ohio State University, wrote a series of papers identifying the genetic basis of the hygienic trait responsible for suppression of AFB. The significance of this important discovery was overshadowed by the apparent success of sulfa drugs and antibiotics in treating foulbrood. Most importantly, the precedent for discovery of a genetic remedy for Varroa destructorwould be rooted in over 30 years of observation and experimentation of hygienic behavior with respect to AFB. It would take another 30 years and the arrival of varroa mites in the U.S. for the lessons learned to be applied again.
More recently, Spivak (1996) describes general hygienic behavior as effective in removing freeze-killed brood and including varroa-infested brood. Several pathways or cues including those chemically mediated (olfactory), mechanical (lack of movement), and thermal (freeze killed) suggesting chemical mediation to be the most probable pathway for varroa resistance (Spivak and Gilliam 1998). Almost concurrently, the Suppressed Mite Reproduction (SMR) trait which involves the breaking of foundress mite reproduction cycles due to removal of pupae by honey bees sensing the presence of mites in the brood, was identified by Harbo and Hoopingarner (1997) with a controlled experiment using queens raised from bees exhibiting good hygienic behavior coupled with artificial insemination of each queen with a single drone. Single-drone insemination results in populations where 75% of the workers are directly related to each other (as opposed to genetically diverse colonies from queens mating with multiple drones in nature) making it easier to isolate desired traits (Rothenbuhler 1964). The presence of the SMR trait was verified by microscopic examination “in the laboratory” of pupae and inventorying mite progeny to determine the status of mite reproduction. It would take about 8 years to rename the SMR trait, now traceable to the hygienic behavior of worker bees seeking and removing varroa infected pupae, to VSH (varroa sensitive hygiene) (Harbo and Harris 2005).
The impact and acceptance of these important discoveries was only moderate according those close to the program probably due to the relative success of chemical remedies, coupled with logistical difficulties surrounding stock maintenance and verification including tedious lab procedures.
Following repeated verification that they had the “right stuff “ genetically, the USDA group at Baton Rouge, who discovered the key role of non-producing mites in supporting Varroa resistance, set about testing practical, “real world” applications for VSH stock. Since much of the previous experimentation had been short term, a three-year experiment was designed involving a group of beekeepers from Alabama. The results showed that untreated VSH bees maintained lower mite populations, therefore requiring less treatments than Russian stock or the control Italians. The Alabama tests also showed that VSH stock provided good mite control in a low stress environment involving stationary colonies for honey production. (Ward et al 2008)
In 2008 scientists at USDA Baton Rouge attempted to confirm the suitability of known VSH/SMR stocks for high stress beekeeping applications involving long distance transportation to multiple crops often characterized by poor nutrition from crops visited, exposure to pesticides and fungicides as well as varroa mites from other commercial beekeepers and their ”in hive” remedies. The first trials involved participation of a highly migratory commercial operation based in Louisiana. This field test used VSH queens outcrossed with drones provided by the collaborator’s “control” stock. These outcrossed VSH bees had a low varroa infestation level at the end of the test comparable to the treated controls vs. the untreated non-VSH controls. These results were verified over a three-year period in which test colonies were monitored through the pollination season involving almond, apples, blueberries and cranberries as well as limited honey production in western New York. The experimental design included VSH queen cells grafted from breeding material provided by Glenn Apiaries of Fallbrook, CA, and the USDA Laboratory, pure Russian queens from several commercial sources as well as control Italian colonies provided by the cooperator. Mite loads for the VSH outcross colonies (untreated) were comparable to treated controls (Danka et al. 2012). Subsequently, queen stock selected from the most populous colonies coupled with the lowest mite loads among the test colonies were used to provide the genetic base for a new honeybee stock, which would come to be known as the Pol-line (Danka et al. 2015). Verification of these results would continue over a six-year period and would eventually include beekeeping operations focused on western honey production and almond pollination migratory routes (Rinderer et al. 2014).
In 2013, the USDA established a technology transfer agreement with VP Queen Bees of Iva, South Carolina where actual VSH queen stock was received from the USDA Baton Rouge laboratory following the retirement of Tom and Suki Glenn in California. (Glenn Apiaries previously had distributed VSH breeding material.) VP Queen Bees’ current approach, which they refer to as VSH Pol-line 2.2 involves development of mite-resistant breeder queens with procedures similar to those used by the USDA laboratory in Baton Rouge regarding development of the Pol-line stock. Cooperating commercial operations provide queens from select colonies with low mite loads and high honey production. Potential queens are tested, cells raised and breeding controlled with instrumental insemination resulting in breeder stock with highly expressed VSH traits. Lamb’s Honey Farm of Jasper, Texas remains a contributor to the VP Queen Bees program. They have developed a method of in-yard selection of mite resistant bees via the alcohol wash technique by screening the best 4 hives in each yard making production a priority along with low mite loads.
Further breeding for VSH- based varroa resistance is occurring in a public-private partnership headquartered at the Hawaii Island Honey Company, near Hilo, HI. Pol-line semen from bees maintained by the USDA laboratory at Baton Rouge is used in single drone inseminations to fast track selection of the VSH traits. The resulting expression of mite resistance in populations is confirmed by field and lab testing methods developed by scientists at the USDA laboratory in Baton Rouge. Confirmation testing is labor intensive and not particularly well adapted to normal commercial queen-rearing operations. The importance of this program and the stock it seeks to produce cannot be overstated. Commercial availability of mated queens and breeder queens is expected in the near future.
MERRIMACK VALLEY APIARIES and EVERGREEN HONEY CO.
For over a decade we have been closely involved with the USDA laboratory at Baton Rouge, LA. We were primary the cooperators (as previously mentioned) in the first VSH functionality test involving nationwide crop pollination, between 2008 and 2010. We were early recipients and testers of varroa resistant Russian queens, and we were among the first to receive some of Dr. Spivak’s Minnesota Hygienic stock, as well as breeder queens from Tom and Suki Glenn, who were the first recipients of VSH and Pol-line breeding material from Baton Rouge and in fact, named the Pol-line stock. In 2018 and 2019, we provided test queens for VP queens.
Currently we produce 30 to 50 thousand queen cells per year for our production hives and our “for sale” nuc program. We have a very aggressive re-queening program attempting to re-queen over 30,000 colonies approximately 1.66 times per year. Due to our large yard sizes (72 to 96 colonies per yard) we flood the immediate area with our chosen queen cells crossed with our drone stock following protocol called for by Spivak and Gilliam (1998), which calls for natural breeding of queens selected for hygienic qualities with resident drones.
After early emphasis on mite resistance in our breeding program, we followed up with breeders from Ohio Queen Breeders providing excellent production stock, while making no claims of resistant traits. Despite crop pollination exposure to many different mite populations from different beekeeper treatment strategies, we have avoided catastrophic varroa epidemics and the effects of “mite bombs” an (example of horizontal mite transmission). The term horizontal transmission (Schmid-Hemple 2011) refers to mite spread from hive to hive due to beekeeping management practices i. e.; pollination proximity, holding yards, uniting of queenless colonies, etc. Horizontal transmission of mites is considered more virulent than vertical (mother to daughter) transmission (Fries and Camazine 2001; Seeley and Smith 2015).
The strength of our breeding program lies in a degree of Varroa resistance, while not highly expressed, is confirmed by reduced frequency of treatment required for mite control. Reduced frequency of treatment is essential to allow the natural resistance traits to be better expressed (Spivak and Gilliam 1998; Locke 2016). Reliance on chemical remedies is counter-productive to natural selection pressure, and can ultimately cause more damage to bee health (Haarman et al. 2002; Johnson et al 2009; Locke 2012). As stated previously, our success in avoiding catastrophic losses is the result of minimal treatment frequency even when mite loads exceed recommended treatment levels. Significantly, the African honeybee, Apisscutellata normally carries and controls varroa mites at the level of 3-4 mites per hundred bees (Locke 2016), a level which triggers recommendation for treatment in European honeybees. It also follows that if mite resistant bees require and receive less treatment, then mites should retain susceptibility to the treatments, therefore reducing the potential to develop resistance to these materials. Reduced treatment strategies require careful mite load monitoring for success.
Beekeepers have options as to the development of their own VSH stock. Breeders are available from VP Queen Bees now and are expected to be available from the Hawaiian breeding program which also expects to sell mated production queens as early as 2020. It would be helpful to have increased verifiable certification of commercial queen producers due to the complexities involved in isolating hygienic traits. The alternative to purchasing these genetics is to adopt techniques exemplified by Lamb’s Honey Farm, also a commercial queen producer, which identify best producers with lowest mite loads and breeds from them. The benefit of this system lies in the emphasis on honey production as a primary qualifier.
We are convinced that long term positive results are possible but will require participation and patience. Claims will be made that will not always prove evident. Improvement will likely be gradual and sometimes seem nonexistent. The first step is to understand the science that has shown it can be done.
The practical application of varroa-resistant bees is perhaps the most important tool for the beekeeping industry to combat mites in combination with minimal treatment. In our beekeeping system at MVA/EVERGREEN, timing trumps mite loads, but there must be some degree of resistance in order to minimize treatment!
A clue to resistance with respect to varroa mites is illustrated by the Asian bee, Apis cerana: these bees and varroa co-evolved and hygiene and grooming developed over the millennia to allow Apis cerana to keep mites at low, non-threatening levels (Peng 1988). It is significant that mite resistant populations of honeybees found around the globe, when exposed to mites have shown natural adaptation without interference from typical apicultural practices, including chemical treatments. If we supply highly expressed, hygienic, Varroa mite resistant traits to U.S. honeybee populations while allowing some minimal treatment, can we have effective varroa control in our lifetimes? If VSH is the bicycle leading us to mite control and treatment is the training wheels, let’s all hope for the day when we can say, “Look Ma, no wheels!!”
Andy Card Jr.
Merrimack Valley Apiaries Inc., Billerica, Massachusetts and Otto New York.
Evergreen Honey Co., Bunkie and Jennings Louisiana.
Park, O.W. 1936. Disease resistance and American foulbrood. Am. Bee J. 74:12-14.
Rothenbuhler, W.C. 1964 Nest Cleaning in Honeybees. IV. Responses of F1 and Backcross Generations of Disease Killed Brood. American Zoologist, 4 (2)111-123.
Peng, Y.S., 1988. The resistance mechanism of the Asian honey bee (Apis cerana) to the mite Varroa jacobsoni, In Needham, G. R., Page, Jr., R. E., Delfinado-Baker, M. Bowman, C. E. (Editors), Africanized Honey Bees and Bee Mites, Ellis Horwood Ltd., Chichester, pp. 426-429.
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Danka, R. G., deGuzman, L. I., Rinderer, T. E., Sylvester, H. A., Wagnener, C. M., Bourgeois, A. L., Harris, J. W., Villa, J. D. 2012. Functionality of Varroa-Resistant Honey Bees (Hymenoptera: Apidae) when used in Migratory Beekeeping for Crop Pollination, J. Econ. Entomol. 105 (2). pp 313-321.
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Rinderer, T. E., Danka, R. G., Johnson, S., Bourgeois, A. L., Frake, A. M., Villa, J. D., deGuzman, L., I., Harris, J. W. 2014. Functionality of Varroa-Resistant Honey Bees (Hymenoptera: Apidae) When Used for Western U.S. Honey Production and Almond Pollination. J. Econ. Entomol. 107:2. pp 523-530.
Seeley, T.D., Smith, M.L. 2015. Crowding honeybee colonies in apiaries can increase their vulnerability to the deadly ectoparasite Varroa destructor. Apidologie 46(6), 716-727.
Locke, Barbara. 2016. Natural Varroa mite-surviving Apis melliferahoneybee populations. Apidologie 47:3, 467-482.