I'll address #4, as I will type a book tackling all 4 at one time...and who wants that.... :roll:
There is not a negative affect on the pests and diseases directly. But it does effect them in so many ways.
First let me say this....
I have studied many feral colonies, and what many have in common is a smaller cavity than what we keep. (If they have a choice, then they will select smaller cavities over larger ones. But I think a lack of old growth trees and a loss of habitat does effect that in that they take what they can get sometimes) They also (again, shown in studies) favor a bottom entrance. In feral colonies, (where beekeepers do not have the opportunity to break the propolis seal every week) they will have the upper part of the chamber sealed tight. Keeping in mind that the R-value in most large old growth forest trees (the ones that probably programmed the bees over millions of years, keeping mind bees came from traditional warmer climates years ago) is more than the 3/4 inch wood we build hives with, and the benefit and advantage of this trapped heat is much greater than what we provide them in our hives. (which is why in theory, I think Warre was correct about heat loss. Although I disagree about opening the hive in summer when it is 90 degrees and claims that this hurts the hive, etc, as Warre claimed or suggested)
So this heat, from an early timeframe of the year is used by the bees to save resources, maintain a larger brood area, and raise new bees faster. *And for anyone who raises nucs, it can easily be seen by taking two frames of bees and placing them into a five frame nuc, and another two frames in a ten frame box. The two frames will expand to 5 frames much faster in the five frame nuc. And it all has to do with the smaller area of the box and the benefits of that trapped heat.
That heat is also shown by the benefits and advantages in things like hive placement. Again, studies have shown that hives in full sun, and in the morning sun in particular, will be more productive, have less stress diseases such as SAC, chalk, etc. The sooner the cluster can break, the faster they can get on with their duties of the hive. Many think that is just nectar collection and foraging. But those duties also include housecleaning, grooming, pest removal, etc. Full sun hives will work early in the morning, later in the evening, earlier in the spring, and later in the fall.
Hives that can not expand fast enough in spring, and must concentrate on duties such as prolonged heating of the cluster and brood, will be less productive, have more pest issues, and have more disease issues on average.
There is a reason why nature has bees go up in the winter and not down. By looking at the natural size of the cavity that bees prefer, this allows the bees to be in a position come late winter and early spring, to best take advantage of this trapped heat, and to utilize it's benefits. That is why having extra boxes, and empty comb, above the brood chamber is not a good idea. And neither is having unnatural amounts of extra boxes of honey, while thinking you are doing them a favor. (another point that Warre was correct about, in having the bees overwinter in smaller volume hives - which is in line with feral colonies and what nature has selected.
The bees are designed or programmed to use much of what they store, be at the top of the chamber come late winter, benefit from trapped heat, and be in a position to raise unlimited amounts of brood as they expand downwards, while storing honey above. And it is the beekeeper that feeds way beyond whats needed, and uses poor manipulation management, that screws all this up. I'm not against doing manipulations, but with the knowledge of what the bees are telling you or have shown you, I think understanding this should be used to a beekeepers advantage.
Warre was correct about hive heat, trapped heat, and such. I just do not take it to the point that opening the hive is as detrimental as Warre suggested. I agree with his concepts of what he has seen in nature, just disagree with his practical approach and what he calls for.
I'm not suggesting that mites will be handled by the mere fact that you have Warre hive. But if you understand the benefits that he was stating (keep in mind - He had NO mites), and couple these IPM strategies, and add others such as Brood breaks, the benefits of young queens, having the best stock you can, and eliminating detrimental issues that many times are just beekeeper ignorance induced....together, they all add up to a beekeeping experience that is successful, and rewarding....and many times outside the box of traditional treatments and the yearly loss that many experience.
Someone once posted photos of infrared pictures of a hive. It clearly had shown the hive cluster position and the outside cluster temp. as well as the trapped heat at the top of the hive. Maybe someone knows where to find these pictures.
And why there is a need for someone to distinguish whether bees purposely heat the hive, or the heat is a byproduct of convenience, is lost on me. The fact is, bees use trapped heat to their advantage, they seek out smaller cavities if given a choice, many time seal the top shut, and are in a position dictated by selection criteria over millions of years, to take advantage of this trapped heat, giving them the best chance to fight disease, raise more brood, be more productive and maintain hive health. It seems a bit more than by chance, that this happens. And it should not be minimized by suggesting they do not do this intentionally. They can not do it because of beekeeper induced situations they can not overcome, but if they had their way, using their own created trapped heat is clearly shown to be an item they understand and use to the fullest extent.
Hope this helps.