"Is this an absolute truth..."
It depends on how slow you want progress to be. We just had an academic cited that had spent 25 years with little or no progress. If that is an ok rate of progress by your standards modest selection pressure is just fine. It might be enough to keep you where you are instead of loss of resistance. Most of us who have actually conducted a few selective breeding studies feel if you can not see measurable progress in AT MOST three generations you are wasting your time and should rethink your whole program so you work on something that may bear fruit in a reasonable time frame. We also had a recent report of significant progress in just one generation of selection for honey production. Some mite resistant projects have shown significant progress in the first generation so progress in three is not an unreasonable target. The vast majority of such programs have not shown any progress at all or even gone backwards. Just look at all the glowing TF programs that ended in year five or seven when winter losses hit 85 or 95%. That includes well known people who give talks all over the country on how easy TF is. Some have even resorted to buying package bees to raise some queens as they were so low on hives and the remaining hives were such dinks there was no other way for them to raise queens.
Dick
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