Leaf-miner flies belong to the Agromyzidae family which systematically belong to Diptera. There are over 3,000 species worldwide, with approx. 350 species in Germany. Domestic species belong to the genus Phytomyza. The species of the genus Liriomyza, which were introduced from America, represent a big problem in particular since they are polyphagous, meaning they can attack various plant species. Leaf-miner flies measure 1 to 2 mm in size. They have a greyish-black base colour and yellow spots. The larvae look much like maggots.
Leaf-miner flies which cause damage to cultivated plants can be found on both vegetable plants as well as on ornamental plants. Females lay their eggs on plant tissue. After hatching, larvae eat through the assimilation tissue of leaves. A female can lay anywhere from 200 to 400 eggs. The larva can fully develop in just 4 days. The larva leaves the mine for pupation. Pupation can take place both on a plant or in the ground. It takes approx. 25 days for the egg to develop into a complete insect at a temperature of 20°C. Leaf-miner flies exist, above all, in the summer months since they prefer high temperatures.
Adult leaf-miner flies damage plants by piercing through them to suck out plant juices. The larvae of the leaf-miner flies create distinct-looking holes (mines) in the leaves of infested plants. The first signs of an infestation are feeding holes in leaf tissue. The miner passageways form within just a few days. The mines can lead to plants ageing earlier as well as leaves falling off. This is not only unaesthetic but also slows the growth of the plant. Heavily infested plants can die.
Make sure to only select healthy plants when purchasing plants. Only insecticides with a systemic effect can be successfully used (absorbed by the roots and distribution of the active ingredient in the plant sap). Adhesive traps can be used to monitor the population as well as to control the infestation by trapping a lot of flies.