"The simplest explanation might be that the cross-breeding of inbred lines
simply allows for reversion back towards a more complete wild-type genome."

I must say I found this statement surprising. Contrast with this from Tom Rinderer:

> Line breeding and hybrid formation were used by G. H. Cale, Jr., to produce the renowned Starline hybrid and later the Midnite hybrid for Dadant and Sons, Inc. (Witherell 1976). These hybrids were produced by developing inbred lines, testing the quality of various hybrids of the inbred lines with other lines, and then rejecting poor-quality crosses.

and W. C. ROBERTS:

You may be interested in some of the history of the development of hybrid
bee breeding. The development of a usable technique of artificial insemination of
necessity preceeded any controlled bee breeding. The work of Watson, Nolan, Laidlaw,
Mackensen and Roberts are well known.

1943 we first tested artificially inseminated queens in colonies of bees. Six
queens were tested and four of these produced worker offspring throughout the four
month test period. In the fall we extracted the first supers of honey that were pro-
duced by offspring of artificially mated queens - queens that had never been allowed
to fly during their lifetime.

Of 490 artificially inseminated queens in 1947 we obtained 395 laying queens
- a percentage over 80% which is larger than would be expected from a like number
of virgin queens allowed to mate naturally in our area. Our test colonies that year
produced an average of 96 lbs. per colony. The highest producing line which averaged
144 lbs. surplus was a 3-way hybrid stock headed by artificially mated queens.

Later work has shown that hybrid vigor is not only observed in certain crosses
but hybridization is the touchstone to success in the production of superior bees.
Hybrid bee breeding will also be important to the development of bees for specific
purposes such as the development of the alfalfa pollen collecting line of bees.

There are, of course, many problems yet to be solved. Since most inbred lines
are weak and incapable of survival in temperate climates without special care and
attention we need to develop better methods of maintaining valuable stocks. 

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