"Science is knowing, art is doing, and common sense is knowing and doing on the basis of experience." Alex Shigo
Over the last few years the beekeeping world has been assaulted by Varroa mites, tracheal mites, and Africanized bees, all of which are problems best solved through bee breeding.The response of the scientific community to these threats has been painstaking research into the natural resistance mechanisms that some bees possess. Today we are confident that several of these resistance mechanisms are effective and practical to breed towards. Bee researchers Marla Spivak and Martha Gilliam sum up the state of the art of breeding for resistance in a recent review of research on hygienic behavior. "Hygienic behavior of honey bees provides multiple benefits for beekeepers with no apparent negative characteristics that accompany the trait......Research has clearly demonstrated the benefits of hygienic bees. Beekeepers should be using this information to improve bee stock." Bee World (1998)The rapid spread of the Varroa mite to beehives worldwide has presented a challenge to bee scientists and bee breeders to develop resistant stock. Both feral and beekeepers' colonies have succumbed by the millions, resulting in loss of pollination of crops, gardens, and wild lands. European honeybees were caught by surprise when the Varroa mite, originally a parasite of the Asian honeybee, jumped to our European honeybee species. The European bees, having no experience with this mite have little defense against the mites. Bee scientists, through careful observation and experiments have discovered several defense mechanisms that are used successfully by the Asian honeybee.
- Hygienic behavior - the ability to recognize and remove mite infested larva.
- Varroa Sensitive Hygiene (VSH) - a varroa specific hygienic behavior.
- Grooming behavior - removing and injuring mites from themselves or another bee.
- Short brood development period - resulting in less time for mite reproduction on brood.
- Longer time spent on adults - as opposed to inside brood cells reproducing.
- Today, miticides are widely used, although Varroa is already showing resistance to these chemicals. Beekeepers long for the good old days when they were not obliged to put miticides in proximity of honey, the most natural of foods. Nearly everyone agrees that the breeding of resistant stock is the best hope for a long term solution to this serious problem.
- Given enough time and in the absence of chemical treatment, European bees would probably become adapted to Varroa by natural selection, as the Asian honeybee has. The goal of the bee breeder is to accelerate this process through artificial selection. This is done by identifying the bees with the desired characteristics and controlling their mating to accumulate these traits in a "closed population." Closed population breeding programs have long been used with great success in the breeding of dogs, cattle, and other livestock. It has only been relatively recently that the mating biology, genetics, and techniques in artificial (instrumental) insemination of bees have been worked out so as to make possible, sustainable closed population breeding programs.
- Research in the last few years has shown that Varroa resistant traits also exist in European bees. Through selective breeding, hygienic behavior and SMR have now been developed to the point of being in practical use by beekeepers. Today it's encouraging to hear more and more reports of beekeepers able to return to beekeeping without the use of chemicals
- The design of a selective breeding program must take into careful account the genetic peculiarities of honeybees.
- Honeybees have a haplo / diploid reproductive system. This means males are hatched from unfertilized eggs, so they have no father and only have half the chromosomes of a female.
- Unlike most animals, each one of a drone's 10 million sperm are identical clones. Sister bees with the same father share 75% of their genes. This is far more than the 50% found in other species.
- The queen naturally mates with up to 20 drones, making the colony a collection of many subfamilies (half sisters with the same mother, but different fathers).
Selection tests
As queen breeders, our role is to take the information gathered by university and government scientists, apply it in our breeding program and then offer our stock to beekeepers. The following are some of the selection tests we are using in our program. See bibliography for more details.
1. Test for Hygienic Behavior
There are several methods of testing for hygienic behavior. They all are based on the rate of removal of sealed brood which has been killed behind the capping. The freeze kill method is the most accurate and preferred for scientific work. Liquid nitrogen can be used to freeze kill the brood in a few minutes. Alternatively, a piece of comb can be cut out of the comb and frozen in a freezer. The pin prick method is less accurate but more convenient, it's the easiest method to start checking the hygienic behavior of your bees.
Pin prick method
Cappings of newly sealed brood cells are punctured with a fine pin to kill the larva beneath. After 24 hours, the number of cells uncapped and cleaned out are counted and recorded. After several replications under different environmental conditions, colonies which have cleaned at least 90% of the cells within 24 hours are considered hygienic. This form of hygienic behavior has been shown to be a significant factor in resistance to Varroa, as well as American foulbrood, and especially Chalkbrood. Genetics of hygienic behavior.
1) Mark a cell directly above three groups of seven newly sealed cells. Use a quick drying paint (e.g. Liquid Paper). Also mark the top bar.
2) Kill all twenty-one larva by pricking them with a pin through the cappings. Use the same hole to prick the larva several times at different angles.
3) Twenty-four hours later count how many cells are completely uncapped and cleaned out. Colonies which have cleaned 19 cells (90%) are considered hygienic.
"The Hygiene Queen" Marla Spivak describes a more scientific method using freeze killed brood.
2. Brood Viability
Honeybees can have a lethal gene which can cause spotty brood patterns. The gene which determines the sex of the bee, is called the "sex allele" . Each female has two alleles, one from it's mother and one from it's father. There are 19 or so different variations of the allele possible (let's call them A,B,C...S). The egg and the sperm each contributes one allele. If the combination is different, (e.g. AB, BC, DE, etc.), a female bee results. 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. Selecting for high brood viability greatly increases the efficiency and productivity of colonies. Low egg viability can be a result of inbreeding and loss of sex alleles. Our closed population breeding program maintains high genetic diversity, thus preventing inbreeding while promoting solid brood patterns.
How to test the brood viability of a queen.1) Cut a parallelogram from a card. There should be 10 worker cells per side, enclosing a total of 100 cells.
2) Place template over the most solidly sealed patch of brood.
3) Count the number of empty cells. Subtract from 100 to get the percentage of brood viability.
4) In this example 100 - 13 = 87% viability. Above 85% is acceptable.
3. Temperament
Our first method is a standardized test given to all colonies in the apiary under the same conditions to be sure gentle temperament is maintained. After an apiary with many hives has been worked, it is often impossible to determine which hives the more aggressive bees came from. A second technique we find useful to separate out any "mean" bees is to capture them in a black plastic bag. Do this by swinging it's open end in a figure eight in front of you, this both attracts and captures the bees. Once captured, the bees can easily be immobilized with carbon dioxide gas or refrigeration and then marked with paint. After being released these guard bees can be found at the entrances of the hives which are then culled from the program because of unacceptable temperament. We select drones and queens from only gentle, workable colonies.
4. Tracheal Mite Resistance (graphic)
The mechanism of resistance against this mite is as yet unknown, but it does clearly exist. Recent evidence suggests that grooming behavior as the mites migrate from one bee to another may be a means of control. Fortunately this trait appears to be controlled by dominant gene(s) and occurs widely in honey bees.
Thousands of bees are examined to determine which hives show resistance. A test can also be done by placing newly hatched workers from various hives among bees known to be infested, for about a week. (Bees are only susceptible to mite infestation when they are very young, up to ten days old). The bees are then dissected and mites in the trachea are counted. Differences in attractiveness or susceptibility to mite infestation are evident.
5. Honey Production and Comb Building
Comparisons of honey production and comb building are made of individual colonies in the same apiary and under the similar conditions. High honey production results from the right number of healthy bees being in the hive at the proper time. Factors enhancing health will likely increase honey production. High honey production using disease resistant stock is the ultimate goal of our breeding program
Why use instrumentally inseminated queens in a breeding program?Honeybees are the only insect which can be instrumentally inseminated, allowing bee breeders to have complete control over the mating of the queens and drones.
Instrumental insemination allows two very powerful procedures which are not possible with naturally mated queens.
- 1. Queens can be mated to a single drone, simplifying selection for specific traits.
- 2. Queens can be mated to hundreds of drones, maintaining genetic diversity.
Breeding for specific traits using single mated queens
- The multiple mating habits of bees has always been an obstacle to progress in breeding bees for specific traits.
- To simplify the selection process, queens can be instrumentally inseminated to single drones.
- All 10 million sperm produced by a single drone are identical clones.
- Queens mated to a single drone produce progeny with extreme consistency.
- Genetic consistency and genetic diversity are opposite ends of a spectrum. One necessarily gives up diversity in trade for "fixing" any trait in an individual, a colony, or a population.
- This genetic trade-off can be optimized using single drone inseminations together with mating other queens with large numbers of drones (supermated).
- Naturally mated queens normally mate with from ten to twenty drones on their nuptial flights.
- Oddly enough, the semen carried in a single drone is more than enough to fill the queen's spermatheca, where sperm are stored for the lifetime of the queen.
- The queen takes a great risk to gather so much extra genetic diversity for her progeny, to the advantage of her colony.
- Recent findings suggest that bees of different patrilines specialize in the various behaviors found in honeybee colonies.
- It is thought that the more genetic options, the more behaviors will be optimized.
- Using instrumental insemination enables the breeder to go one step beyond nature and inseminate the queen with hundreds of drones.
- Drones are chosen from colonies expressing desirable traits such as disease resistance, high honey production and gentleness.
- Semen is extracted from hundreds of drones from many colonies, mixed together, then used to inseminate many queens. We call these queens "supermated".
- Supermated queens have very high brood viability due to the high diversity of sex alleles, which means more bees in their colonies.
- By maintaining a high degree of genetic diversity the negative effects of inbreeding are avoided.
- Supermated queens contain many times the genetic diversity of naturally mated queens. They are excellent as breeder queens in breeding programs to prevent unintentional inbreeding.
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