Bee Management
My wife was in the teacher's lounge and one of her co-workers asked if she'd been breast-feeding a smurf. It turned out that a blue pen had leaked in her shirt pocket. My apologies if I offend. Regarding your question:
Bees are attracted to yellow, much like hummers are attracted to red.
I like to use feeders without bee guards, since guards are extra ugly with regard to photography, as well as being a nuisance to clean. I immediately throw away the little plastic floweres, bee guards, and perches on any hummingbird feeders I have. I even use wire cutters and cut off perches if that's necessary. That way I get more photos of hoveriing birds and fewer of perched birds. The birds don't seem to mind much.
Anyway, back to bees. My carpenter bees never seem to bother my feeders, so perhaps that's because I DON'T use bee guards!
When honeybees swarm my feeder, a short term measure is to move the feeder (gently) to a different location, and hang a bee proof feeder where the feeder originally was. Often the bees can't find the moved feeder, after a short time, and then you can take it in the house anc clean it. After a few hours, you can rehang it, or hang it elsewhere. The key here is that bees take a while to discover a nectar source, and can't find a feeder immediately if it's moved about 20 or 30 feet. Once the ones one it leave, it takes a while for others to return.
The "permanent" solution is to use an absolutely bee-proof feeder. That's a saucer type feeder, which is a little flying saucer, with an ant trap in the center, a brass hook to hang it by, and a clear plastic ring to hold the necter.
The ring has a red lid, with ports on the top for feeding. Nectar NEVER touches the port When you carry the feeder, carry it by the hook, and the nectar won't slosh up against the rim of the lid, which can leak, and the ports. If you're pretty careful filling and carrying it after cleaning and filling it, there will be NO sugar on the outside of the feeder, and therefore nothing to attract the bees. They can't get to the sugar through the port, and aren't attracted anyway. Perhaps they'll discover it after the birds have sponged nectar from the feeder onto the port with their tongues, but this is a very small amount, and bees don't generally find it.
I also modify my bottle-style perky-pet feeders. As I said, I discard the flowers, perch, and bee guards. I saw off 3 of the 4 ports, and plug them with hot glue. Then I use a drill (1/4 inch, I think) and enlarge the hole in the port, and insert a little "nipple" of clear plastic with a star shaped slit on the end. I bought this at a bird supply store in the hummingbird section. This keeps the port "closed", but allows the bird to insert it's tongue or beak. It serves to almost totally eliminate dripping from inverted bottle style feeders, and it works great. Without extra nectar dripping below the spout, bees are less likely to find the sugar. Use care when drilling the hole larger, the wall of the port tube will be quite thin. Use a port brush to clean the port, it's hard to get the port-star-thingy in and out. I just leave mine in place. I prefer my modified perky-pet for photography. The birds approach the feeder from a wide variety of angles, and so you get more interesting poses. With a saucer style feeder, you get them hovering level above the dish, only, unless they react to the click of the shutter. They you may get a good acrobatic shot as they are startled by the shutter. Flash doesn't really bother them at all, except that they learn to blink, just like you do, when their photo is taken several times in a row, so you get some closed-eye shots.
Back to the bees: I find in Arizona in the spring that there is a short period where the bees are very active. I hang orange halves in the trees to attract orioles. When the orioles find the orioles find the oranges, they first eat the bees, and then eat the orange. Maybe it's a coincidence, but perhaps the bees pass the word that my campsite is dangerous to bees, and they stop coming around so much. Perhaps that's my imagination. Or perhaps they swarm feeders most in early spring when there aren't many flowers in the high desert yet. (I had snow on the ground just a few days before my worst bee problems! this was in Mid-march.)
Anyway, some of these techniques may be of assistance when trying to protect hummers from bees.
Re-reading your post, I see that you're from europe (I think) and therefore have no hummingbirds. You can invert what I said to see that a bottle style bird feeder, with the port painted yellow (and bee guard removed) would be an excellent bee feeder. I think the same 1:4 nectar formula would be great, it sure attracts bees just dandy. With regard to numbers, I've seen at least 50 bees on a feeder at once. I doubt you can get a perky-pet hummingbird feeder in europe, but they have a flat bottom which can accumulate a lot of nectar drippings, and has a big surface area to support them. you could make one by drilling a hole in the bottom of a bottle, capping it tightly, and hanging it up. Any drops leaking from the bottom would tend to accumulate acoss the base. A wine bottle might be great for the purpose. You can buy drill bits which are designed to drill through ceramics and glass, and they're not hard to use.