Better Stock for Beekeepers
Bee Culture
(January) Vol. 136 (1): 17-19
By
Malcolm T. Sanford
It looks like the time has
come to look much more closely at stock improvement. Finally, the beekeeping world is beginning to
tread the path that plant and livestock breeders have pioneered over the last
four or so decades. It has not come easy
and only appears to be happening because beekeeping is inexorably driven toward
this response due to the ravages of exotic organisms and subsequent use of
chemicals inside the beehive. In the
final analysis, it appears that the honey bee in fact has become more
“domesticated.”1
Many are now coming the
realization that genetic improvement is considered the best long-term solution
to the many problems beekeepers face today, whether it be managing mite
populations, controlling viruses or attempting to solve the CCD dilemma.. The idea is not new; for generations
beekeepers have known and practiced that most universal solution for when their
colonies failed, replacing the queen. This
has always been both an advantage and curse, because so much genetic potential
is involved in one individual. The bees
know this as well, the reason so much diversity has been programmed into the
natural mating process.
A pioneer in bee breeding
whose work will be more appreciated in the future was Dr. Walter Rothenbuhler, a prominent honey bee geneticist from The
Ohio State University. I wrote a homily
to Walter in the March 2003 Bee Culture.2
One of his most thoughtful and valuable contributions
on his favorite subject was published in a two-article series in 1980.3
He began his series with
“Ever since beekeepers have known that queens and drones mate in flight, they
have felt somewhat powerless to engage in bee breeding. It is true that certain queen producers have
grafted from carefully selected queen mothers, but very little control could be
exercised over the drones with which the virgin queens mated.” Even though there have been some improvements
Walter concluded, “no great change in the bees of
Walter then listed the
following research that was needed and had been done in order to have better
genetic control:
Since Walter’s paper, there
have been other developments showing the value of selection, including Varroa mite resistance (SMR/VSH), careful introduction of
resistant Primorski stock (Russian bees), and the
incorporation of genes from “survivor colonies.” In addition, there is evidence for genetic
resistance to tracheal mites in honey bees and dominance of Africanized honey
bees in the tropical lowland environment.
In 1992, I wrote about the possibility
of developing a stock center based on ideas presented by Tim Lawrence and Susan
Cobey.4 They concluded this
would be an expensive endeavor. At that
time, I said, “Some might not understand what skills are involved in bee
breeding and how these might be reflected in the costs of a stock center.
“Thus, I am reprinting a
slightly edited version of a presentation on queen breeding I received via
electronic mail. It is not likely to be published elsewhere in the
The difficulty in improving
stocks, according to Mr. Yanke, is based on the
following barriers:
1. CONTROLLING MATING BEHAVIOR: It has been shown that virgins very rarely mate with related drones, which reduces the chances of inbreeding, one of the perils to avoid in any controlled breeding scheme. Thus, if we allow virgins to mate naturally, we have no control over the drones. Even with isolated mating yards, control is not absolute. What other plant or animal breeder has to make an attempt at genetic improvement with only control over 1/2 of the genetic equation? To compound this there are multiple matings. Each virgin mates with seven or more drones, and thus the colony is made up of seven or more sub-families.
2. RETAINING SEX ALLELES: In most sexually reproducing organisms, sex determination is governed by a sex chromosome. In honey bees, however, sex is determined by a single gene. This gene has many variants or alleles, maybe as many as 18. One should feel lucky, however, to maintain 10 or so in a breeding population. It works like this, if two different alleles come together at fertilization, a female (worker or queen) results. Drones are haploid and have one allele. However, if two of the same allele come together, a diploid male results. We never see diploid drones in the hive because when only a few hours old, they are cannibalized by the workers. Evidence of this is a hole (spot) in a slab of newly capped worker brood.
As the number of sex alleles decreases, the more likely it is that two of the same allele will come together, increasing the number of diploid drones. As the percentage of diploid drones produced increases, so does the spottiness of the brood. There is an obvious impact on a colony's productivity, therefore, when some well-intentioned bee breeder reduces the number of sex alleles in a queen. Even if such queens are of high physiological quality and genetic potential, they are handicapped because a percentage of their eggs are not viable.
3. REDUCING INBREEDING DEPRESSION: Hybrid vigor results when two unrelated members of a species are crossed. The vitality of the progeny usually exceeds that of either parent. This is also known as heterosis, a mostly unexplained increase in life force. The crossing of unrelated parents results in many more genes carrying two different alleles. When a pair of genes consists of different alleles the resulting organism is said to be heterozygous. A generalized increase in heterozygosity is responsible for triggering heterosis. The opposite state is when genes carry two of the same allele. These organisms are said to be homozygous.
A reduction in heterosis occurs with inbreeding. An "inbreeding depression" is triggered as the percentage of homozygous genes increases. This results in an unexpected loss of vigor--sluggish colony build-up, loss of disease resistance, decreased production, and higher winter loss.
Inbreeding depression can result from selections over generations for the best genetic combinations. The breeder's downfall is increasing the percentage of homozygous genes in too small a population. This is not always apparent to a producer who is selecting breeders from perhaps hundreds of colonies. Unfortunately, it is not the size of the test population, but the number of breeding queens used, which determines how quickly inbreeding depression develops.
4. MAXIMIZING QUANTITATIVE TRAITS: The characteristics we are trying to improve in honey bees are quantitative traits. These may involve many genes, each contributing only small effect. Compounding this is the fact that these traits are not those of a single breeding individual (the queen) but, instead characterized in a colony composed of many sub-families.
It is fortunate that many important economic traits such as honey production and winter hardiness in bee populations, even though they are hugely complex, and controlled by a large number of genes, do show good response to selection. However, once these selections cease, any increase in traits which has been achieved is lost very quickly as gene frequencies return to pre-selection balances. Thus, maximizing quantitative traits is a continuous process which must be done with great care.
5. MINIMIZING ENVIRONMENTAL VARIATION: Evaluations must reliably identify the genetically superior individuals in the test population in order to increase quantitative traits. However, because colony performance is evaluated in the field, it is difficult to control environmental influence. Possibilities to reduce environmental effects consist of equalizing colonies before evaluations begin, minimizing drift; and eliminating evaluations between apiaries. Finally, because a queen's physiological quality itself can have a major effect on some aspects of colony performance, queens undergoing evaluation must be uniform in age and condition.
6. MINIMIZING THE INFLUENCE OF RACIAL HYBRIDS: Even if we implement all the suggestions above, and put into evaluations the care and effort required, it is all for naught if the genetic superiority we identified with our evaluations is not heritable. Unfortunately, the increased vigor provided by heterosis cannot be inherited.
We have two races of honey bee in
To get anywhere, we have to breed true to race -- whatever that race is. The Dark European honey bee drones appear to be very aggressive in the drone congregation areas because they appear to have a mating advantage of almost Africanized-bee-like proportions. So the only way to keep a test population true to race is to have absolute control over the mating using Instrumental Insemination.
7. KEEPING AN OPEN MIND: It may be a lot cheaper to import a silk purse, than to try and make one out of a sow's ear. Taking advantage of different races and breeding work done overseas by importing genetic material could save time and money and be a dramatic shortcut to better bees. Times have changed, importations of genetic material can be done safely, whether they be semen or breeder queens.
Returning to Walter’s paper, he stated that much of the work he referenced produced only information. It was not designed to supply better bees to beekeepers, but to learn how to get better bees. To supply better bees to beekeepers is a greater task he concluded. It will take three links in a chain, 1) field tests, 2) genetic decisions, and 3) commercial production. What has been mostly missing is the second link.
The geneticist, according to Walter, must provide input for the nature or the field tests, how data will be taken and number of colonies tested. In addition he/she must help decide which colonies are to produce queens and drones for the next generation and when instrumental insemination or natural mating should be used. Finally, the geneticist must help decide how to maintain improved stock over a period of years and how to release it to beekeepers.
The complexity of any breeding project is now apparent, Walter concluded: “Someone must manage the whole affair and see that the three components interact cooperatively and creatively on a continuing basis. Almost as an after though he said; “It may be apparent also that a considerable amount of financing is required.”
This goes back to the idea by
Tim Lawrence and Susan Cobey referenced above that
bee breeding is a costly enterprise. The
biggest question facing the industry then is not whether superior stock can be
produced, but whether or not beekeepers will continue down the same road they
have in the past resulting in cheap queens that produce unproductive and
disease-susceptible colonies. It seems
abundantly clear that “you get what you pay for,” and beekeepers will have to
say goodbye to inexpensive queen bees in the future if they wish to be
successful in managing healthy, productive colonies of honey bees.
References: