Sounds like leaf miner. We used to get it all the time on our lemon tree in Perth... along with aphids, scale and some disease which peels the bark. Despite being anti-chemical for many, many years, I am now a convert to carbaryl. This is a contact poison with no withholding period. I use it to combat cherry slug, which were killing my cherry trees. I also used it to get rid caterpillars which were eating the buds of my pernnials and roses. Go and ask at you local gardening shop - you will find there is a great range of organic sprays available now. Take in a leaf so they can see what you need the spray for.

Thanks Robyn, I haven't wanted to spray with white oil in the seering temps as I was told it would burn the leaves even more. Don't think they could look much worse though. I hoped feeding the tree and keeping it healthy might help but I suppose as it's a "predator" that may be inconsequential. I'll ask agin at the Nursery.

Check out this site for positive identification of leaf-miner.

Carbaryl probably won't affect the leaf miner because the little critter will be protected inside the leaf. White oil is fairly innocuous and one of the very few insect control measures I use (on scale insects). It is not a poison - check out http://www.afcd.gov.hk/agriculture/eng/pso_e.htm

You could also remove the affected leaves, secure them in a plastic bag and put them in the bin - no more moths to hatch out to lay more eggs.

Here is a link that might be useful: http://www.dpi.qld.gov.au/business/7320.html

Just found a recipe for a homemade white oil - vegetable oil and Sunlight dishwashing detergent. Check site for instructions.

Here is a link that might be useful: http://www.abc.net.au/brisbane/stories/s780287.htm

I have had lemon trees do this ie get curled and unhealthy looking leaves, but in my case I don't think it is caused by a "sucking bug". I think it is more likely to be that the soil conditions are less than optimal. It is a possibility that your tree is still suffering root trauma from the transplant. I have found that lemon trees take a long time to recover from traumas.

I can't honestly say I've used this on much other than bromeliads and gardenias, and I would be worried about the sun too.
But MP put me on to this concoction which is called "Dr Bob's Salad Dressing" made from Canola oil and supposedly breaks down a lot quicker than the commercial white oils. Just a thought.

Here is a link that might be useful: canola white oil mix

It might be both, as Giacomo said shock and because the tree is weak it is more susceptible to insect attack. Remember the oil treatment, whichever you choose does not kill the leaf miner, it prevents it from entering.