Advice re swarm care needed

I live in southern california. Recently a small swarm appeared in a mimosa. There are already two families living on the land, in hollowed out sections of palm trunks made for that purpose, into which they voluntarily moved. When the new swarm appeared I made a sort of nuc box based on a video online and positioned it by the trunk of the mimosa, and smeared the entrance with homemade lemongrass oil. Over the following week I also sprayed lemongrass tea around the front of the box. Nearly a month later and the swarm is still there, although its size seems diminished. Initially I wasn't worried and accepted their apparent rejection of the new box, thinking that perhaps they were already involved with bulding another home somewhere else. As time has gone on and they're still there, I've begun to worry more, especially as over the last few days the size of the blob has seemed to shrink. There' isn't much chance of rain at the moment, but the nights are cold, down to about 8C. I'd really like for them to stay just to have around, I've no intention of molesting them or taking their hard-earned food. Any insights as to what could be amiss with them and what what would be the best course of action from me for them would be much appreciated.

Do you have a bee suit? It sounds like you might need to physically capture them, stick them in a hive box, & block them in for a while. You could try contacting your local beekeeper association for some help.

Sometimes the lemongrass oil fragrance can be too much for the sensitive bees. If you used anything but 'a bit', it might be too much.
You could try to rub some of the oil off and place a bit of old honeycomb/brood comb, if you have it, inside the bait hive.
Good luck!

Thank you both for your rapid replies.

Nina, I see your point, and thinking about it it that does make sense given how sensitive they are to subtle pheromonal hints. I think I may have I overdone it with a liberal smearing of oil. Unfortunately I don't have any old comb, having used what I found in an old home to fut into the previous log homes I made. I put the last of the wax I had along some of the bars in the new box.

Mike, I don't have a suit having never intended to so intrude into their life that one would be necessary. I have net and a wide brimmed hat that would serve the purpose, and work gloves into which I could tuck long sleeves, but what would be the thinking behind doing what you suggest, especially blocking them in? From my perhaps overly sensitive position that feels like a forceful involuntary move. I know it's being suggested 'for their own good' but I'm mindful of other forced relocations that have been done for the same reason. As I say, perhaps overly sensitive. I only know of one professional beebotherer in this area (when I said southern California I meant Baja California), and I don't like his attitude toward bees, which if it were human to human would be called mysogynistic. What to do?

Again, thank you both for your input.

It is common practice to plug the exit holes with grass after placing a swarm inside. In the time it takes them to remove the grass they have generally accepted their new home.

Nearly a month later and the swarm is still there, although its size seems diminished.  

That sentence leads me to believe that the bees probably have no queen & will perish.

If a queen stops laying or dies & there are no very fresh eggs for the workers to make a new queen sometimes the bees leave & swarm as you describe. Unless they can be added to an existing colony with a queen they will gradually die off. When they swarm with a queen they usually find a new home quite fast.

Are they building combs on the branch they are staying on? Bees in the south will sometimes nest in the open.

If they have been sitting in place for more than a week they will have started making comb and are highly unlikely to move without intervention. It is normal for a new swarm to shrink in numbers initially - from when they first swarm they have a certain number of adult bees. From the they will be steadily losing numbers until the next generation of larvae emerge as adults, and even then they don't start foraging duties for typically two more weeks. So expect about a 5 week lag from a swarm first settling to then seeing an increase in bee numbers.

And all of the above depends on suitable conditions for foraging for nectar and pollen, warmth for raising brood, and enough wax for queen to lay eggs in, and enough bees to care for the brood. And if the queen is not laying properly then nothing will help.

When we had bees, dear hubby gave them a sugar water solution of 50/50 sugar to water.

I would suggest that this might help those bees.

Thank you all for your insights, I wish I'd come here earlier.

Mike, I had read of the possibility of a swarm with no queen, and thought that might be the case here.

Michael & Thom, there was no comb visible, and the blob was so small, enough to cup two hands around, that I doubt there was much going on inside it. Most of the flowering trees and plants here are either in between flowering or only just starting to flower. I live in an oasis in the desert, so suspect there wasn't much to forage further afield. With that in mind I'd moved a hummingbird feeder from the other end of the land where it was common to see bees from the other family sharing with the hummingbirds, but the blob didn't show any interest.

Following your advice, Mike, this morn I went up to let them know I'd be moving them today, and found the branch bare. As there'd been a big hand-sized blob there yesterday, that they'd moved seems more likely than died off.

Again, thank you all for your insights. I'll save them for the next time,  this sort of thing having happened several times already. Perhaps it's time to get a suit and take a more proactive position.

It sounds like they moved. Mother Nature know best!