Citrus leaf miner (Phyllocnistis citrella) has four life stages: egg, larva, pupa, and the adult moth.
Adults do not damage plants and live only 1 to 2 weeks. Adult moths are most active in the morning and the evening and spend the day resting on the undersides of leaves, but are rarely seen.
After mating, the female lays single eggs on the underside of host leaves. On the tree, the newly emerged leaflets of flush growth, particularly along the mid vein, are the preferred egg-laying sites. If your trees are small enough you can regularly inspect the leaves and brush off the eggs before they hatch – about 1 week after being laid.
The newly emerged larvae immediately begin feeding in the leaf and initially produce tiny, nearly invisible, mines. As the larva grows, its serpentine path of mines becomes more noticeable. The larva emerges from the mine as a pre-pupa and rolls the edge of the leaf over causing a curling of the leaf. Again by constantly inspecting the leaves on your trees you can remove these leaves with the moth pupa and reduce the number of moths.
Female moths avoid leaves sprayed with plant based horticultural oil. This can be either a commercially available organic oil or you can easily make your own by mixing 2 cups of vegetable oil with ½ cup of dishwashing liquid in a blender.
Store this concentrate and dilute 1 tablespoon in a litre of water and spray both sides of the foliage. Be careful to follow this dilution rate, because you can burn the foliage if it’s too strong.
Don’t apply it in hot weather and avoid using it on plants with hairy foliage as well as ferns, palms and cycads as this can also cause leaf burn.
Spraying should coincide with new growth flushes.
Although Mandarin trees and Meyer lemons are particularly prone to citrus leaf miner, I have found that they affect all of my citrus including orange, tangelo and grapefruit.