Good advice here
Just by looking at the picture I bet the pot is the problem. It looks like it takes a long time for it dry out.
How fast does the water run out when watering? How many holes are in the bottom? How big is the hole(s)?
That pot looks like a death trap!
I recommend Orthenex Insecticide (insecticide, mite-icide and fungicide all in 1) it should control your insect problems.
Read, Use and follow the label! Make sure you use this outside or in and area you are not going to stay in.
Indoor bonsai is difficult the do and even harder to master.
I would recommend getting an indoor bonsai book by Paul Lesniewicz
http://www.google.com/search?hl=en&...G=Google+Search
Also
http://www.bonsai-bci.com/species/serissa.html
drowning in your pot, redhawk