In August 2001 I discovered two leaves on a seedling Pummelo which showed signs of the patterning produced by this insect. The leaves were fairly old and I found no more, so I destroyed the leaves, read up a little more about this pest, and wasn't too concerned.
But a week or so later, at dusk, I saw two small, fluffy, white flying insects which immediately reminded me of the descriptions of the moth stage of the Citrus Leaf Miner, Phyllocnistis Citrella. I managed to squash one, but succeeded in catching the other to investigate it further.
The moth-like insect was about 2mm long.
This picture of it was taken with my toy QX3 microscope at X60 magnification.
Unfortunately, it matches exactly other pictures I've seen of the Citrus Leaf Miner.
Having confirmed the presence of this moth, I made a more thorough investigation of my potted plants, concentrating on new growth. It didn't take me long to find the other stages of the pest.
This is the typical snaking track of the larva as it eats its way along the underside of the leaf. The larva itself is clearly visible at the head of the track. It leaves behind an area of leaf covered with a shiny film. The leaf portion shown is about 20mm long.
The larva works it's way to the edge of its leaf, where it hides under the rolled up edge to pupate. Again at X60 magnification, here the larva is at the pupa stage - it is beginning to metamorphose into the adult moth.
The resulting leaf damage is shown below - back and front of the same twig from a Bears Lime.
The 'mined' leaf begins to develop yellow patches. These become prey to moulds, turn brown and eventually form ragged holes, so leaving unsightly leaves with contorted edges.
So, what to do now?
Well, I expect this is a pest I will now have to live with. Chemical control is difficult and will destroy the beneficial insects present. For the moment, I have picked off all infected leaves I could find and thoroughly re-sprayed all my plants with white petroleum oil. The adult months are said to try and avoid oil sprayed areas when looking for somewhere to lay their eggs.
page updated 09 May 2004
UPDATE: I eventually decided I had to make every possible effort to eradicate this pest. So, following professional advice, I obtained the commercial insecticide Dynamek with active ingredient 'abemectin'. This spreads through the leaves to control leaf miners. I have sprayed twice, and so far have found no more living larvae. As a bonus, all citrus red mites also seem to have gone.This is still the case some ten months after first discovering the pest.
UPDATE TWO YEARS LATER: I have had no more cases of the citrus leaf miner. Citrus red mite has returned at intervals, but the Dynamek spray is still giving good but decreasing control.