Age Of Queen For Insemination

Whenever possible, inseminations should be made at the normal mating age of the queen, around the seventh to 10th day after emergence. We have inseminated queens successfully in quantity as early as the fourth day. They can be inseminated at any later age so long as they have not started laying. The minimal interval between two inseminations should be 1 day, and a 2-day interval will permit a more complete clearing of the reproductive tract when very large doses of semen are given. In this connection, oviposition may start as early as 2 days after the second exposure to carbon dioxide. There is some evidence that when development is retarded by cool weather, inseminations are more successful at 10 to 12 days than earlier.

Procedure For Various Objectives

The number of inseminations and volume of semen will depend upon the objective of the inseminator and the time and effort he is willing to expend. Usually only one or two inseminations are made. The efficiency, that is the percentage of sperm reaching the spermatheca, decreases as the amount of semen injected increases. After insemination with 2 to 20 microliters of semen, the percentage of sperm reaching the spermatheca will range from about 15 to 4, respectively. Results will vary with the stock used.

In bee breeding and genetic studies it is often necessary to inseminate a queen with semen from a single drone. For best results with such individual matings, well-nourished drones reared in large cells in relatively new drone comb should be available and only those utilized that ejaculate perfectly and yield a large quantity (1. 25 to 1. 5 microliter ) of dark cream-colored semen. Results will depend upon the stock used. One might expect about 10 to 15 percent of queens to be partial or complete ''drone layers" immediately and more to become ''drone layers" later. Some may lay fertilized eggs two seasons in a nucleus. The spermathecae of 17 queens killed soon after insemination contained an average of 0. 87 million sperm (range: 0. 22 to 2. 24), about one-sixth the number found in naturally mated queens.

If a queen is expected to produce fertilized eggs for a few months only and individual mating is not required, an insemination with semen from three to four drones (3 to 4 microliter. ) will be sufficient. Average spermathecal sperm counts of 2. 9 and 3. 6 million have been reported after insemination with 4 microliter.

If a queen is to head a large colony for a year or more, it is logical to attempt to duplicate the number of sperm a queen receives in a completely satisfying natural mating. On the average, naturally mated queens receive about 5 million sperm in their spermathecae. Experiments have shown that queens that have no desire to make further mating flights after their first mating contain an average of 5. 3 million sperm in their spermathecae. Further experiments have shown that queens do not mate naturally after instrumental insemination with 8 microliters semen, but do fly out for further mating if given smaller amounts. The number of sperm reaching the spermatheca with a dose of 8 microliter. semen has been reported as 3. 16 and 5. 4 million in different experiments. Although the number of sperm reaching the spermatheca increases as the dose increases, diminishing efficiency makes it hardly worth while to give more than 8 microliter. of semen in a single insemination. Also, with higher amounts the danger of injury is increased. In some experiments a high death rate was obtained with single inseminations of 12 microliter; in others, 18 microliter was the maximum given without injury.

If a certain quantity of semen is given in two inseminations of equal amounts instead of in one insemination, the number of sperm reaching the spermatheca will average about 15 percent greater. (Increases of 1 to 41 percent have been reported. ) Another advantage is that variability will be lower. These advantages must, however, be weighed against the additional effort involved and the additional chance of injury during the second insemination.

The percentage of laying queens obtained will vary with stock used, but an experienced operator should be able to obtain 90 percent laying queens after either one or two inseminations during the most favorable part of the season if the stock is vigorous and disease is absent. Properly inseminated queens have been shown to perform as satisfactorily in brood and honey production as naturally mated queens.

Queens that are already laying can also be inseminated, but egg production must first be reduced. The technique is most commonly used in mating a queen with her own drones to attain a high rate of inbreeding. The virgin queen is first induced to lay by treating with carbon dioxide. When her drones are mature she is caged away from her colony with a few attendant bees for about 4 days to stop or retard egg development. Then she is inseminated as usual but with small amounts (3 microliter. or less) of semen to avoid congestion in the oviducts in case some eggs are still being produced.