Agriculture Reference
In-Depth Information
the breeder's apiary. Controlling the drone brood and the propagation of drones from
exceptional colonies are, therefore, part-and-parcel of the line-breeding process. This
improves the stock's male parentage but, obviously, this procedure can be employed
effectively only in those areas where mating apiaries can be isolated.
The main problem with line breeding is that a fixed population of bees means that
some inbreeding is inevitable. This reduces the stock's vigour, the result being a poor
brood pattern. Inbreeding can, however, be minimized by rearing queens from as large
a number of outstanding queens as possible and when possible, by re-queening all the
colonies with queens from other breeders.
Is line breeding, therefore, worth the effort? The answer to this question must be yes. In
the USA in the 1930s, for example, a four-year line-breeding selection project resulted
in an increase in honey production from 67 to 181 kg (148 to 398 lb) per colony. Two
important features of this project were the culling of poorer queens and grafting from
the best queens.
Hybrid breeding
When inbred lines or races of bees are crossed, the progeny are often superior to either
parent for one or more traits. This phenomenon is called hybrid vigour or heterosis,
and little is known about it apart from its effects. Hybrid-breeding programmes are
more complicated than line-breeding programmes and involve the use of artificial
insemination. At the minimum, three inbred lines must be combined so that both their
queens and worker daughters are hybrids.
According to John Harbo and Thomas Rinderer in the USA, comparative tests of bee-
breeding programmes have demonstrated the superiority of hybrid over line-breeding
techniques. For example, increased productivity of 34-50% over the average has been
reported in hybrid as opposed to line-bred strains of bees. The one big problem with
this type of improvement, however, is that you have to keep on crossing. Hybrids are
an end product and, to make the best use of them, it is necessary to re-queen every
year - you can't breed from them to continue a line of successful bees. Because of the
complexity of this type of breeding programme, and because of its requirement for
