My Own Experience.
There is NO definitive data on TBH manipulations. I stumbled on adding bars to the brood nest by experimenting to see what would happen. At the same time I was researching everything I could find on the net and came across Dennis Murrell and his study of the importance of the core brood nest. I combined his theory with what I wanted to accomplish and came up with this.
I increased the population of my TBH’s by making gaps between brood combs and adding empty bars and it worked but the hive failed in the second winter I was also treating with FGMO at the time.
Turns out the FGMO kept the mites below the economic threshold for that winter and the hive survived into the second season. I drew a wrong conclusion and attributed the success to strength of the colony. Next season I did not treat it and it absconded early fall with signs of PMS.
I tore it apart and started measuring cell sizes and discovered that the natural cell sizes on the original combs were 4.9 to 5.1 and I had divided that grouping by adding bars which were drawn out to cell sizes of 6.0 to 6.1 drone combs. The grouping I refer to was the core brood nest Dennis was referring to.
The bottom line was I added stressors to an already stressed colony and it succumbed.
This is what I am doing today:
Because I believe in splitting the brood nest to increase population I avoid splitting the middle and only come in one bar from each end and leave it at that. That does not mean you did not disturb the core nest as location varies. I would like to adjust this manipulation to avoid disturbing the core brood nest all together But I do not have enough data to determine if there is an ideal location to add bars and not do any damage. I will continue to investigate this. If you keep this manipulation limited to a spring tactic and don’t rush things along the bees should have enough time to establish a core nest and clean it in early fall. This much I have seen in my hives with my own eyes!
I also did not treat this hive thinking it was good now…….wrong again!
Second great discovery:
A colony cannot go cold turkey and survive mites, just can’t be done at least not here with Carnicas.
If I find a drone comb bar I save it and every time it is capped freeze it and give it back to the bees to clean out this is my drone culling method instead of cutting drone comb out.
Sugar dusting and a sticky board to monitor mite fall
The economic threshold of a colony occurs when the mite population exceeds the bee population and the host parasite relationship is thrown out of balance. This usually occurs in the fall when the bees are forming their winter population/cluster size. Your job as a beekeeper is to keep the balance by insuring the mite population stays at a level the bees can handle which is as small as we can possibly get it! How you do this is entirely up to you. Your second job as a beekeeper is to make sure that what you are doing to manage the populations is not so intrusive that the bees decide the land lord is too nosey and the look for better accommodations!
Limit your manipulations to the spring early summer.
Limit your intrusions all together.
Time your treatments to correspond to a rise in your mite count.
Remember you will probably reach a point where your mite counts do not warrant treatment for a while BUT never stop monitoring. The honey bee is a very stressed creature pesticides etc, etc, etc, Even though the colony has seemed to beat mites it has NOT it is just reached a good balance add a NEW stressor and the mites will get a better foothold and the colony is out of balance again! And you are standing there wondering what happened to your mite resistant bees.
All this is the result of loosing my hives every season even this year I am starting from scratch AGAIN. My theory is to know how to save them we have to know what is killing them, why it is killing them and how it is killing them! I have learned a tremendous amount watching the bees react to what I did or didn’t do!
I am by no means an expert in the field but I was willing to take the losses to get to a sustainable future. This season I fully expect to bring a majority of my colonies thru winter 08 with no problems.