The little squiggly line damage that you see on your citrus leaves is caused by the larvae of a small moth. It lays its eggs in the leaf tissue and when these hatch, the tiny larvae feeds inside the leaf creating the characteristic silvery tunnels.

Although older trees can usually sustain some damage, younger trees can be severely affected. Large infestations can retard the growth of young trees and cause the leaves to twist and curl. 

Insecticidal control is difficult because the larvae are protected with in the leaves. Horticultural oil sprays reduce numbers by affecting the egg laying. The tiny moths will avoid surfaces sprayed with oil, so regular spraying will prevent them from laying.

By fertilising in late winter, new growth flushes will be promoted when the leaf miner is rarer as they like to burrow in new leaves. Once the leaves have hardened, they are resistant to leaf miner attack.