Unsightly leaves at the tips of new citrus branches are often caused by citrus leafminers. They originate from a tiny moth that lays eggs only on new citrus tree growth. Its larva then tunnels around inside the leaf, eating between the top and bottom surfaces of the leaf. This insect's activities cause the leaf to curl as well. While it makes a mess of new growth on citrus, it does not do significant damage to larger trees, and even very young citrus trees are unlikely to be permanently damaged. The
UC Citrus Leafminer Pest Note has more detail about the life cycle and how to manage it.
Along with other details, the Pest Note says: