>> Obviously, Apis cerana  has some form of defense that it uses against the varroa. Perhaps this could be transferred to Apis mellifera?

>        The idea that any such trait is based on only one gene, or on some very small package of genes, is implausible.

In fact there are many behavioral honey bee traits that can be traced back to a handful of genes, among the most famous are the 2-3 recessive loci (or discrete non-segregating chunks of DNA) that impart hygenic behavior, whereby workers abort brood cells before foulbrood can sporulate or varroa have offspring.

Nonetheless, intuitively I am drawn to Robert's arguement, there is a big difference between taking discreet genes within a species and shuffling them around compared to moving genes among species.  Genes work in the context of other genes, and putting a bacterial gene in a honey bee is at a much higher risk to fail than just moving honey bee genes around; IMHO it is too foreign a context to expect things to be in balance.

I will make a case, however, that even if single gene resistance to varroa is available, through classical breeding or transgenics, it cannot expect to hold up for very long.  Throughout agriculture there are numerous examples of single gene solutions to keep a crop protected by a pest or disease which do not last long.  Take the numerous variaties of wheat with single gene resistance to Hessian fly or Bt-transgenic lines of corn resistant to corn borer; it does not take long for resistance to break down.  Resistance of this kind is no better than applying a pesticide in terms of resistance management.

The most successful cases of resistance are those which involve many many genes working in concert.  Resistance of this kind is not easy to breed for, and maintaining lines once established can be a nightmare, but once established pests and diseases are hard pressed to overcome them.  Returning to the case of honey bee hygenic behavior, the character was first discovered by investigating a beekeeper's line, the Brown line, came about by repeatedly selecting for bees that survived on comb with AFB scale, NOT by selecting for hygenic behavior.  Further investigation into the Brown line found that not only was hygenic behavior at work, but resistant characteristic carried by the developing larva was also at play.  Many characters at work rather than one leads to more robust resistance... it only stands to reason.

But single-gene resistance varieties of crops are far more common than varieties in which multiple genes confer resistance.  Why?  It is easier and faster to screen and maintain lines based on a few genes than on many genes.

What does this mean?

Lines incorporating a few genes that confer resistance will give immediate relief and the quickest results, which of course is what the industry needs today.  If, however, we also consider the long term health of bee stocks, large breeding programs to select for lines with multiple gene resistance to pests must also be considered.

There is no such thing as a free lunch.

Regards
Adony

Adony Melathopoulos
Apiculture Biotechnologist
Agriculture and Agri-Food Canada
Beaverlodge Research Farm
Box CP 29
Beaverlodge, Alberta CANADA
T0H 0C0

T +1 780 354 5130
F +1 780 354 8171