Hi - why would you want fruit on a bonsai, unless the fruit was very small, like cherries or berries, because fruit and flowers don't reduce as leaves do and full size lemons will topple a bonsai unless it's very large. As far as the spots go, they could be anything from insects to signs of fungus from watering too often (more likely I think), but without anything else to go by... How are you growing it otherwise, in what kind of mix, in how many hours of sun daily, and how often do you water?

Post a full pic of the tree, please.

Meyer are a bit tricky...they like a lot of nutrients, regularly. How are you feeding the tree? Also, the leaves don't reduce very well.

Like Moochinka said, it's best to develop the tree into a bonsai without fruit, then let it develop just a fruit or three for the final showing....which you'd probably do in alternating years.

The other thing about Meyer....if you pull flowers, it'll make more flowers, and that will use up a lot of energy. So, when you do get fruit, and do intend to pull it, let it grow to nearly marble size before removing the fruit.

Josh