i wouldnt say they lose thier appetite...but they are not growing as much, or as fast as they were when they were younger, so they dont need to eat as much. also every gecko is different, so some may eat alot more as adults than others do. if your gecko has started eating less, i would check and make sure nothing in his or her habitat has changed. if nothing has changed, and your gecko is still acting normal...eating(even if less), pooping, drinking, and everything else is normal, i wouldnt worry about it at all. the only thing you should watch for if everything else is normal, is weight loss. you can tell by the thickness of the tail or buy a digital scale, that measures in grams. also keep your eyes open for other obvious signs that something may be wrong. you can get the scales from Staples and other office supply stores from around 40 dollars and up. is there a specific reason for the question, or just curious? just curious myself, because if something is off, there are alot of very knowledgable people here who will gladly help you out! good luck and keep us posted.