Leaf Miners

General

The American serpentine leaf miner (Liriomyza trifolii) originates from North America, but occurs also in Europe since about 1976. The American serpentine leaf miner (Liriomyza trifolii) is highly polyphagous and thus lives on many host plants such as chrysanthemum, gerbera, gypsophila, celery, sweet pepper, pea, bean and potato. In greenhouses, it is mainly found on gerbera and chrysanthemum. Today the insect is widespread across the whole world.

Life cycle and appearance of American serpentine leaf miner

The life cycle of a leaf miner has the following stages: egg, three larval instars, a pupal instar and the adult fly. Adult leaf miners are small yellow and black coloured flies, at most only several millimetres long. When the adult females feed or lay eggs, they bore a hole using their toothed ovipositor, usually in the upper side of the leaf. Egg spots are oval and hard to distinguish from feeding spots.

The larvae of Liriomyza trifolii are entirely ochre-yellow. When the larva hatches from the egg, it begins to eat into the leaf at once, tunnelling down into the mesophyll tissue where damage is caused by extensive mines, leaving the outer layers of the leaf intact. Shortly before pupating, the grown larva cuts a sickle-shaped exit hole in the leaf with its mouth parts. After roughly one hour the larva crawls out of the leaf and falls to the ground. This occurs in the early morning. The larva crawls into the ground to pupate. A small percentage of the larvae remain hanging on the leaf and pupate there.

Damage symptoms

Leaf miners cause damage to plants both directly and indirectly. The most direct damage is caused by the larvae mining the leaf tissue, leading to desiccation, premature leaf-fall and cosmetic damage. In tropical and subtropical areas this can lead to burning in fruit such as tomato and melon. Loss of leaves also reduces yield. In full-grown plants of fruiting vegetable crops, however, a considerable quantity of foliage can get damaged before the harvest is affected.

The older larvae make wider tunnels. Feeding spots made by adult females can also reduce yield, although except with ornamental crops, this is usually of less significance. Seedlings and young plants can be completely destroyed as a result of the direct damage caused by leaf miners.

In gerbera, the larva of the American serpentine leaf miner (Liriomyza trifolii) eats its way outwards from its egg, so that its mines join to form small plates. In various other crops one finds intermediate forms of tunnelling between these ‘plate mines’ and normal mines, making it an unreliable criterion for the identification of the species.

Indirect damage arises when disease causing fungi or bacteria enter the plant tissue via the feeding spots.

How to get rid of American serpentine leaf miner

Adult leafminer flies are very small (only a few millimeters in size), and they’re yellow and black in colour. The female fly cuts a tiny hole in the leaf of the host plant and lays an egg inside. The larva that hatches is a small (3 mm long), white or greenish-yellow, translucent maggot. It begins to feed on the leaf immediately, consuming the soft inner tissues while leaving the outer layers intact. When the larva is ready to pupate, it cuts an exit hole in the surface of the leaf and drops out onto the ground. It then either burrows into the soil or finds shelter in a crack or crevice and transforms into a small pupa, which can range from light yellow to black in colour. Sometimes pupae can be observed still hanging from the underside of leaves.