Chris, I am new with adenium too, but here is a suggestion that might help.

Type in "adenium leaf drop" in the search box(upper right corner of your page). I got over 100 posts where this problem is discussed.

Hope this helps. Hang in there!

Chris, the leaves dropping off can be a normal occuence with Adeniums.
They drop their leaves when going into dormancy. As long as the stems, caudex (girth or base above soil) and roots are firm and clear of any rot, then it should be fine.
Sounds like you have already examined your plant and the roots are clear of rotting.
As for the ants. I have found that if I have had mine outside for the summer and the pots are sitting right on the deck. The ants or wood bugs will go into the pots.
I keep mine now all up off of any solid surface with pot feet or on my plant stand. Also, keeps them from ever sitting in water being of the ground.
Changing the soil was a good move.
Please check back.
Rick

".... so I sprayed some insecticide and ant powder into the soil."

There isn't enough information to identify the problem precisely, and it isn't 100% clear whether the yellowing and leaf loss came before the insecticide applications or after.

If the leaf loss/yellowing was before the spraying and ant powder, I'd guess over-watering, that it's part of the plant's natural rhythms; or, if it came after the insecticides, that one or both of the insecticides might have been toxic. Were they labeled "for use on plants"? Many ant powders contain boric acid, which can easily deliver toxic levels of boron, and the vehicles (what the active ingredient is dissolved in) of many aerosol insect sprays are toxic to plants.

Al

It could be overwatering? With Adeniums
based on where you reside (climate) and conditions made available. This is a process in which adeniums go through (loss of leaves, dormancy). Especially during this time of year, with lower light levels and temps.
You are the only one that will know whether you have overwatered.
Do not know that active ingredients in your ant killer and am not informed enough to give an answer on this.
As tapla mentioned, with information given. Can make it a
difficult to pin point.
If you search at the bottom of the Adenium forum thread there is a bar in which you can search out most queries.
The information and articles that Tapla has created about soil, water retention and such are very helpful
and worth a read. We are fortunate to have very knowledgeable people here, so please check these out.

This post was edited by rcharles on Sun, Nov 30, 14 at 15:22

Thank you everybody for the advise that you ve given to me because I am very new here, at first I didn't find this post has been answered, so I asked the same question again on my other post. I so sorry for that, anyway I will do as what you guys have mention and thank you so much.

Hi everyone, i just bought an adenium and the store owner helped me to transfer the plant to a newly purcahsed pot with red soil, 火烧土 or 红土 as generally called. It has been a month now, all the leaves have turned yellow and shed. The plant is now bald. There are flowere but they are weak and do not appear majestically solid and firm. Some flowers are not properly formed. The miserably few leaves that are visible are turning red on the underside. Is adenium beyond hope?