Leaf miners are tiny grubs that damage the internal layers of the leaves structure. They are commonly found on fruit trees, vegetable crops and other outdoor plants. They leave a distinguishable trail of brown, white or opaque lines on the leaf’s service where the grub has ‘mined’ through the layers of the leaf. These lines are called mining scares and can be easily seen on leaves and stems. If left untreated, they can cause severe damage to the plants.
A female leaf miner can lay up to 160 eggs in 13 days.
How To Identify Leaf Miners
There are several species of leaf miners (Agromyza, Cerodontha, Chromatomyia, Liriomyza, Phytomyza and Pseudonapomyza genera); however, they all leave very distinguishable trails. These trails are made by the larvae of tiny months from the Gracillariidae family. They’re around 4mm in size and are unlikely to see them due to their small size. Their trail is their more identifiable feature.
Life Cycle of Leaf Miners
The most common adult leaf miners are yellow and black coloured flies, only 4mm long. The adult female lays eggs by making holes in the leaves, known as egg spots, using her toothed ovipositor. These holes are called feeding spots as the leaf exserts nectar due to the damage.
When the larva hatches from the egg, it eats its way into the leaf. They tunnel down into the mesophyll tissue (middle layers), where extensive mines cause damage. The outer layers of the leaf and stalk stay intact, but the tunnels are visible externally. As the leaf is damaged, fungi and bacteria can enter the feeding areas, further damaging the plant.
Before pupating, the grown larva cuts an exit hole in the leaf with its mouthparts. Then, the nymph crawls out of the leaf, falls onto the ground, and pupates in the soil. Finally, an adult leaf miner will emerge from the pupa. Within 13 days, the female can lay up to 160 eggs.
Where Do Leaf Miners Come From?
Leaf miners are the larvae of tiny moths or flies of the Gracillariidae family. About 500 specials of this family occur in Australia, but the most coming one is Citrus Leaf Miners. As pupa, they can fly from plant to plant, spreading quickly. They look for sweet nectar from flowers, citrus or vegetables.
A female leaf miner can lay up to 160 eggs in 13 days. She’ll cut a small hole in the leaf and deposit eggs near the hole, making easy access for her larvae.
Leaf miners originated in South-East Asia, but many variants have formed during the globalisation of plant species.
What Leaf Miners Eat
Leaf miners feed on plant nectar, from flowers to honeydew. Citrus leaf miners feed on the mesophyll tissue (middle layers) of the leaf, eating down to the stalk of plants.
They suck the nectar out of the plants, and with high numbers, they make photosynthesis impossible and slowly kill the mother plant.
Natural Ways To Remove Leaf Miners
Pesticides are the most common method to remove leaf miners. However, timing is everything when it comes to leaf miners, as if you spray too early or too late, the pesticide will not reach to larva or kill the flies.
The most effective natural pesticide is neem oil.
Spray all your outdoor plants in early spring to prevent any flies from landing on your plants. Once you have an infection, you need to act fast. First, spray every leaf of the plant, focusing on the underside of the leaves.
Don’t forget to spray the soil of the plant.
The soil will be infected as the larva drops into the soil to transform into a pupa. Spraying the ground with neem oil will suffocate the transforming leaf miner preventing them from fully developing.
Pluck off any infected leaves. Adult leaf miners make holes in the leaves, making them vulnerable to fungi and bacteria. Prevent the spread by removing the leaf. Repeat this process weekly. A female leaf minder can lay 160 eggs in 13 days, meaning you need to repeat treatment.