Regarding whether to eat the holey leaves. I would certainly eat the one on the right but not the one on the left. Nothing to do with the holes but the left one just looks too old to be palatable. If those holes are representative of the type of damage you're getting I personally wouldn't do anything except give the plants a good shake and maybe a blast from the hose. I don't know what Bt costs in the States but here it is extremely expensive and almost impossible to find for sale. I don't know why. It has to be ordered from the US and the postage at least doubles the cost. I wouldn't bother going to that amount of effort unless I had a massive problem and my livelihood depended on a perfect crop. A few holes are par for the course and will do you no harm.

Removal wasnt intially an option for me, but when you (and the other half, she refered to it as "letting it die a slow and natual death") put it that way, it makes sense. The tree is spotty all the way around. The only real area it is providing shade to is that back corner(back right in the picture). There arent any other shade trees in the area, so a replacement would definately be necessary. Throwing good money at bad, more than likely. Cutting it down and replacing with a properly placed, planted and taken care of tree may be a great option. Anyone have any ideas on how much it would cost to chop this sucker down and get some fire wood? I could also use some browns for the compost pile, or maybe some nice mulch? Another thing I have to consider is that my city does not like trees being removed An inch of replacement tree for each inch of DBH removed or "30 inch or greater DBH, $50.00 per inch removal" Unless: The tree is diseased or injured to the point it will ultimately expire or no reasonable remedy exists The tree is in immedite danger of falling and no economically praticable remedy exists The tree is significantly endangering existing structures so that its continued presence will ultimately cause damage and no remedy..... In the citys professinal opinion the tree is substantially endangering existing pavement or utility services in a manner that threatens to damage property or life The tree creates unsafe visibility that pruning will not rectify It is found by the city to be in the interest of the general publics health, safety and welfare that the tree be removed. I will be making a call to thecity tomorrow...

Bit hard to work out from the photos what exactly is happening. The best I can make of it is that some species of wood boring grub is in the tree. Could be wasp or beetle larvae. I don't know which ones you might have there but probably best you check with your local agricultural department. Termite damage can also look like that but do you have termites there? If it were here I'd say Mastotermes darwiniensis, but not in Singapore.

No, it's not the ants. It looks like normal rot from part of the tree dying. The ants are probably carpenter ants, cleaning up the dead wood. Have you had extended drought there in the last 5 years or so? IME, Populus tremuloides or quaking aspen don't like it dry for very long and will start to die during a long drought period. Once the rains return they will grow vigorously again but the damage is done, on the inside. Not much you can do. Remove the tree and start another one, maybe one more suited to the site.