Author: Des Cannon
In the March 2017 Issue of The ABK (p. 391) I answered a question put to me about lack of eggs and larvae in a hive, and I discussed queens and the possible need to replace a queen. A subsequent discussion on this topic with a commercial beekeeper raised an issue that I had not taken into account – the fact that the lack of eggs and larvae, even in the presence of an apparently healthy queen, could also be due to the queen having a high level of inbreeding in her genetic makeup. This could be the result of poor genetic diversity, or it could be due to the way in which the queen (or the queen breeder that was used to produce the queen) was herself produced.
A number of commercial beekeepers have expressed to me this season their dissatisfaction with queens purchased from some commercial queen breeding. At the time I thought it was probably due to poor mating conditions early in the season, but there is also a strong possibility that it could have been due to some level of inbreeding in the queen breeder’s operation. Think about it – if you purchase queens from a queen breeding beekeeper, and a consistent 25 % of them are ‘duds’, and you go back to the supplier and finds that he himself uses 4 queen breeders as the source of larvae to raise his queens, then you have to at least consider the possibility that 1 of his 4 queen breeders has a high level of inbreeding.
The following article is an attempt to explain why this is the case, and to explore the question of inbreeding and its effect upon colony viability.
A study by Brock Harpur, of York University in Canada, and colleagues, reported in a 2012 issue of Molecular Ecology, stated widespread collapse of bee colonies in many parts of the world is not due to a lack of genetic diversity. Examining the theory that ‘Human management and selective breeding are believed to have caused reductions in genetic diversity in honey bee populations, thereby contributing to the global declines threatening this ecologically and economically important insect.’ Harpur and colleagues found evidence against this.1
They found that managed honey bees actually have higher levels of genetic diversity compared with their progenitors in East and West Europe.
Professor Ben Oldroyd of the University of Sydney found similar genetic diversity of managed bees in Australia. Oldroyd thought diversity in managed bees can be explained by the fact that beekeepers' regularly import new queen bees from many parts of the world, and then these queens mate with feral bees.
This is not to say, however, that inbreeding cannot occur within the queen bee breeding operation of any one beekeeper, or across the operations of a number of beekeepers. It depends upon their own breeding program, or in the absence of any breeding program, upon the operation from where they source their breeding queens.
The Effect of Inbreeding upon the Viability of the Queen
Inbreeding is a powerful tool for creating genetic diversity but it depresses performance, particularly in components of reproductive fitness including fertility, viability and production traits (Dickerson,1973).2
Research workers investigating apparent low egg viability in inbred lines discovered that sex in bees is determined by the alleles at a single locus. If an egg is a heterozygote at this locus, it will develop into a female. If it is homozygous or hemizygous, it will develop into a male.
The apparent nonviable eggs found in the inbred lines were diploid eggs homozygous at the sex locus. Worker bees selectively remove and destroy homozygous diploid larvae from the comb just after they hatch. If two of the same allele variations happen to occur at fertilization (AA, BB, CC..), the egg is eaten immediately upon hatching. This special circumstance creates a male bee known as a diploid drone, which is never allowed to mature in the hive. This is a cause of what beekeepers know as "shot brood," when as little as 50% of the brood survives.3
Research efforts have been made to rear these diploid drones to maturity with the hope of producing diploid sperm and triploid queens and workers. However, artificial rearing is a difficult procedure, and the resulting diploid drones had reduced testes and produced very little sperm.4
Line Breeding 4
The common method of breeding practiced by queen breeders is known as line-breeding. It can be defined as breeding and selecting within a relatively small closed population. The bee breeders’ colonies constitute such a population to the extent that mis-matings with drones outside their stock do not take place.
The general procedure in line-breeding is to rear queens from the best colonies. These queens are both sold as production queens and used to requeen the bee breeder’s test colonies. The queens are allowed to mate with the drones present in the bee breeder’s outfit at the time the queens are reared.
A number of variations can be made on this general procedure which would be of benefit. General control of drone brood in the majority of colonies, coupled with purposeful propagation of drones in a good number of more exceptional colonies, would improve the selection progress by controlling, to a limited degree, the male parentage of the stock. Of course, this procedure is used with the best success in areas where mating yards can be reasonably isolated.
In line-breeding, some inbreeding is inevitable. Its main effects are
(1) fixation of characteristics so rapidly that effectiveness of selection for good qualities is reduced,
(2) the stock loses vigour as a general consequence of inbreeding, and
(3) the poor brood pattern from homozygous sex alleles. These effects can be lessened by
using as many breeding individuals as possible for every generation.
To keep inbreeding at a minimum, one should rear queens from as large a number of outstanding queens as possible and requeen all the field colonies with equal numbers of queens from all the breeders. Each group of queen progeny is then considered a queen line and each year, after testing, at least one queen in each line is used as a grafting mother.
Despite these several precautions against inbreeding, stock may begin to show a spotty brood pattern and other symptoms of inbreeding. When this occurs, new stock must be brought into the operation. At least 10 virgin queens from each of several promising stocks should be mated with drones of the declining stock and established in apiaries outside the mating range of the beekeeper’s queen-mating yards. They should be evaluated there to determine which stock(s) combine best with the deteriorating stock. Once this evaluation is made, the preferred stocks can be established as new queen lines.
When inbred lines or races of bees are crossed, the hybrid progeny often are superior to either parent for one or many traits. This phenomenon is called hybrid vigour or heterosis. Hybrid bees have more heterozygosity in their genome than do inbred or line-bred bees. This heterozygosity is thought to be the basis for hybrid vigour.
Hybrid-breeding programs in bees are considerably more complicated than line-breeding programs. At the very least, three inbred lines must be combined so that both queens and their worker daughters are hybrids. An inbred queen mated to inbred drones will produce hybrid workers. However, the egg-laying qualities of the inbred queen probably would be inadequate. Therefore, there is a need to mate hybrid queens to inbred drones so that both queens and workers in production colonies are hybrids.
Comparative tests of hybrids have shown their superiority. Increased productivity of 34 to 50 percent over the average of line-bred strains has been reported. Segregation and random mating in the generations following hybridization are likely to result in queens that are no better than the average supersedure queen. Hybrids are an end product, and to make best use of them it is necessary to requeen every year.
Whatever the specific choice of breeding scheme, hybrid breeding requires the use of instrumental insemination and careful recordkeeping. As a consequence, few bee breeders have undertaken the entire operation of a hybrid program. However, many have become involved as producers of hybrid queens with the breeding stock supplied by an outside source.
1. ABC Science Bee colony collapse not due to inbreeding
2. K. Bienefeld, F. Reinhardt, F. Pirchner. Inbreeding effects of queen and workers on colony traits in the honey bee. Apidologie, Springer Verlag, 1989, 20 (5), pp.439-450.<hal-00890799>
4. John R. Harbo And Thomas E. Rinderer Breeding and Genetics of Honey Bees
BEEKEEPING IN THE UNITED STATES, AGRICULTURE HANDBOOK NUMBER 335
Revised October 1980: 49–57
5. Randy Oliver What’s Happening To The Bees? – Part 4: The Genetic Consequences of Domestication American Bee Journal, May 2014