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Mite Tolerance In Honey Bees
Mite Tolerance In Honey Bees
By: Malcolm T. Sanford

A variety of factors are being explored.

October 10, 2004

Dr. Tom Seeley s article in the July 2004 Bee Culture is a pleasant surprise.1 It seems that honey bees infested with Varroa mites and have not been treated with chemicals are doing just fine in the Cornell University s Arnot Forest. Well, to be more accurate, I find it pleasant, certainly, but not a surprise. The fact that honey bees can take care of themselves in spite of being subjected to the ravages of an introduced, exotic species, the external (outside) parasitic mite Varroa destructor, which has been responsible for the death of so many managed colonies, should astonish no one. This has already been seen in bee populations in the wilds of Western Russia near Vladivostok (Primorski stock) and reported in Serbia with Carniolan bees (Apis mellifera carnica), giving rise to Yugo stock. Hints of it have shown up elsewhere in Europe, which has a much longer history of mite infestation than the Americas. Finally, it is taken for granted in Brazil, where a huge beekeeping industry is beginning to flourish in spite of the universal challenge by these mites.

Now that what was obvious to many has been firmly established, Dr. Seeley will bring his considerable talents to bear on subsequent questions. What is the mechanism for this tolerance? Is it avirulence, the concept that if vertical transmission (from mother to daughter colony) is the major route of infestation, then there is a selective advantage to parasites that do not kill their host? Or is it evolution of bee resistance or tolerance to the mite? These are not mutually exclusive, according to Dr. Seeley, which means they might occur together, providing another level of complexity. Given what I know about biology, I am placing my bet that both are involved.

Another introduced mite has and continues to be a problem for beekeepers in North America, especially in temperate climates. This is the internal (inside) mite, Acarapis woodi. A similar situation in finding tolerant honey bees to tracheal mite exists as that for Varroa, although the inside mite does not appear to be generally as damaging as the outside one. In the best known case, a breeding program in Europe, developed by a monk at Buckfast Abbey, Brother Adam, produced a population of apparently-tolerant bees.2 I am using tolerant here, but the word resistance is also used by some, and there is discussion in scientific circles about which is most appropriate. Buckfast bees were brought to the Americas and used in Canada and New York to help beekeepers establish other lines. Over time in most areas where tracheal mites were a problem, their virulence has dropped considerably.

According to Dr. Robert Danka, the mechanism for tolerance (he uses the term resistance ) is that populations of tracheal mites are reduced by honey bees grooming themselves (autogrooming).3 He concludes: It does not appear that differences in cuticle chemistry, the presence of hairs surrounding the prothoracic spiracles, or grooming among nest mates are major determinants of resistance. Perhaps, but there has been evidence that the transfer of mites from bee to bee may be affected by these or other mechanisms, the reason that vegetable oil patties appear to be effective for control. Finally, he concludes: resistant bees cause little or no reduction in fecundity of tracheal mites which infest them.

Dr. Danka says there are three possible stock selection scenarios that allow queen breeders to cultivate tracheal mite resistance in stocks:
1. Newly emerged bees are placed in mite-infested colonies and then examined for mite loads. Mothers of those bees having fewer mites after being exposed are selected for further breeding
2. Mite infested bees are divided among colonies. Queens from colonies with less overall infestation after a period of time are selected for further breeding.
3. Natural selection gives rise to resistance by abandoning any use of chemicals and selecting from colonies that survive and thrive the best under such conditions.

>P>Scenario number one above is a technique pioneered by Dr. Medhat Nasr (now Provincial Apiculturist in Alberta, Canada) while working with the Ontario Beekeepers Association. He believes beekeepers in most areas cannot discount tracheal mites damaging colonies.4

The situation surrounding Varroa is more difficult than for tracheal mites, yet similar when one looks at the practical breeding methods being used to fix tolerance in populations. Dr. Marla Spivak says that in general Varroa population growth is influenced by:
1. Successful entry of a mated female into a brood cell containing a 5th instar larva.
2. Successful reproduction of the mite within the cell (at least one mated female offspring).
3. Probability that the same mite will survive to enter another brood cell.
4. Number of complete reproductive cycles a mite completes in one season.

Like the situation for tracheal mites, effects of genetics and environment come into play. Dr. Spivak divides her discussion into sections entitled: mite environment and genetics, bee environment and genetics and current breeding programs. 5

Major unknowns regarding the Varroa mite s environment have to do with its reproductive success on adult bees (the phoretic or hitchhiker stage) and on the developing pupae and larvae. Mite genetics certainly plays a role. We now know several haplotypes (genetic varieties) of Varroa exist, some (Korean) more virulent than others (Japanese).6 Where each haplotype is most common and how it interacts with the bees and colony environment in different locations is for the most part unknown.

The bee environment, both internal (nutritional status) and external (temperature, rainfall), also may affect Varroa reproductive success. Studies in the tropics appear to reveal that bees in the lowlands and hot areas are more tolerant than those in the cooler uplands. Honey bee genetics plays a huge role in differences among races from tongue length to body size around the world. So it should too when considering tolerance to Varroa. Africanized bees (Apis mellifera scutellata) are thought to be much more tolerant to Varroa than Europeans (Apis mellifera ligustica), but there is evidence they are less so in Mexico than in Brazil. Evidence also exists that even pure European honey bees isolated on an island for many years off the coast of Brazil are tolerant. Again, this may be due to the kind of mite present.

Africanized honey bee biology, however, appears to favor some of things thought to be responsible for tolerance: 7 According to Dr. Spivak, these can be summarized as:
1. Shorter post capping period, meaning there is less time for mites to complete reproduction.
2. Increased grooming of both themselves (autogrooming as found in tracheal-mite-tolerance) or among bees (allogrooming).
3. More uncapping and removal of infested larvae and pupae by adult bees, the hygienic behavior thought to be responsible for some populations being resistant to American foulbrood.

No one is suggesting that Africanized bees be imported for developing tolerant stock, although populations are living happily in the southwest from Texas to California. Current breeding programs do exist to fix Varroa tolerance in European bees Dr. Spivak reports. These include those that:
1. Select for a single trait such as grooming or hygienic behavior. Carniolan Yugo bees fit that category.8
2. Import stock and select from a population known to be tolerant. Most often this is from an area where there has been no treatment for a number of years and so-called survival colonies can be found. This is the case for Russian bees.9 Dr. Seeley s bees in the Arnot Forest are likely candidates as are other populations that might be discovered in the future. Populations have also been reported at Tucson Arizona s USDA Bee Lab.10 The latter case showed there was no significant interaction between tracheal and Varroa mite infestations, and Africanized honey bee stock was not necessarily a cause of tolerance.
3. Select for suppression of mite reproduction (SMR). This is a program pioneered by Dr. John Harbo and colleagues at the Baton Rouge Louisiana s Bee Laboratory.11
4. Select for a group of characters that allow colonies to survive without treatment. The Honey Bee Improvement Program in the UK12 and Sue Cobey s New World Carniolan Project fit this model.13

Dr. Spivak says: If colonies are bred from the survivors of untreated colonies, some degree of resistance in the progeny may be obtained, but it is important to understand the reasons why some colonies survive. The most efficient breeding program should be based on selection for characteristics that have the greatest impact on reducing mite survival and reproductive success, and those characteristics should be heritable.

Many questions remain, according to Dr. Spivak who concludes, there are no beekeepers or researchers who have successfully bred a line of bees that is Varroa resistant or tolerant such that they (sic) can survive without treatment. These questions include:
1. Is it realistic to attempt to breed a line of bees that never requires treatment by miticides?
2. Is it sufficient to breed lines that survive without treatment for one or two years?

There is little doubt that some success in the search for tolerance, the most sustainable and difficult long-range solution to any mite problem, has been realized. However, much more needs to be done if this holy grail in beekeeping is to be used on a routine basis. In the meantime, Dr. Seeley will continue his inquiry to determine how the bees or the mites or both critters are changing and adapting to one another in nature s constant search for stability (homeostasis) among its living organisms.

1. Seeley, T.D. 2004. Forest Bees and Varroa Mites, Bee Culture, July, pp. 22-23.

2. Buckfast Abbey web site, accessed July 19, 2004.

3. Danka, Robert, 2001. Resistance of Bees to Tracheal Mites, in Mites of the Honey Bee, Hamilton, IL: Dadant & Sons, Inc., p. 122. See also: Baton Rouge Bee Laboratory web site, accessed July 19, 2004.

4. Mississippi Department of Agriculture Newsletter, January 2002, accessed July 19, 2004.

5. Spivak, Marla, 2001. Honey Bee Resistance to Varroa Mites, in Mites of the Honey Bee, Hamilton, IL: Dadant & Sons, Inc., p. 206.

6. Sanford, M.T. 2000. Varroa destructor: A New Name for an Old Parasite, Apis Newsletter, University of Florida, IFAS, July,, accessed July 19, 2004.

7. Sanford, M.T. 1997. Varroa Tolerance in Honey Bees, Apis Newsletter, University of Florida, IFAS, August, accessed July 19, 2004.

8. Honey Bee Genetics home page, accessed July 19, 2004.

9. Glenn Apiaries home page, accessed July 19, 2004. See also de Guzman, L. I., T. E. Rinderer, G. T. Delatte, J. A. Stelzer, L. Beaman, and V. Kuznetsov. 2002. Resistance to Acarapis woodi by honey bees from far-eastern Russia, Apidologie, 33: 411-416. Reported at files/, accessed July 19, 2004.

10. Erickson, E.H., A.H. Atmowidjojo and L. Hines., 1998. Producing Varroa-Tolerant Honey Bees, Tucson Bee Laboratory, accessed July 19, 2004.

11. Sanford, M.T. 2001. Specific Issues on the Web The SMR Selection Site, Bee Culture, March,, accessed July 19, 2004.

12. Bee Improvement and Bee Breeders Association web page, accessed July 19, 2004.

13. New World Carniolan web page, accessed July 19, 2004. See also, Sanford, M.T. 2003. Sue Cobey & Her New World Carniolans, Bee Culture, January 2003, pp. 21-23.


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