Looks like a case of an enormous number of spider mites sucking the life out of your small trees.

I agree with jean...spider mites. If you jump on the problem right away, you should be able to control the mites on two small trees.

thanks for the help, guys that was exactly what I needed.
I've been looking up pictures, and they match exactly with the damage I'm seeing.

I've also been reading threads on how to handle them, and I'm hoping it works.

being in Costa Rica, I don't have access to Neem oil or buttermilk, which some folks recommended. I'll try with diluted alcohol and repeated sprays to see how it goes.
thanks so much!!
Jimena

BUTTERMILK?? That's a new one on me, Jimena! Where did you read that; I am so curious!

Be sure to direct your alcohol mists to the underside of the foliage, where the mites hang out. You will also find that sprays of plain water, on a frequent basis, will help.

I found it here, believe it or not!! a lot of people swear by it
http://forums.gardenweb.com/forums/load/brug/msg0412125830776.html

I've misted them twice, and so far, none of them seem to have dropped dead from the alcohol. these guys are irreplaceable, so I'm pretty jumpy about hurting them. I've been using a solution of about 4/1.