Liriomyza spp.

Scientific Name Liriomyza Mik, 1894
Common Names English: Leaf miner; Spanish: Mosca minadora; German:Minierfliege; French: Mouche mineuse
Description Small flies, between ca. 1.2 and 2.5 mm long, generally yellow and dark gray or black in color. In some species the ovipositor of the female is easily noticeable. Larvae are typical maggots, legless and without head capsule, up to 3mm long and whitish, in some species bright yellow or yellowish-green.

Biology

Damage

The adult females carry out numerous punctures into the leaf surface for oviposition as well as for feeding on the sap that leaks from the injured leaf tissue. The feeding-points appear as white-yellow „stipples“ all over the leaves.
Worse, however, is the damage caused by larval feeding. The larvae will tunnel through the mesophyll of the leaves, leaving the epidermis intact, thereby producing characteristical, unsightly „mines“, often with the frass inside clearly visible. If these are numerous, the reduction in photosynthetically active leaf surface will slow down plant development, young plants or seedlings may even die.

In temperate regions vegetables grown in field culture will show mainly cosmetical damage that may reduce marketability. Ornamentals can be too blemished to be sold at all. In warm areas and glasshouse cultures, where the fly's generation time is shorter and population densities may increase rapidly, damage will be much more severe in all crops.

Lifecycle

The genus Liriomyza comprises nearly 400 species, which can only be reliably identified by laboratory examination. Most of them are rather monophageous, feeding on weeds and considered economically unimportant. Only a few leafmining flies, especially the species L. huidobrensis, L. trifolii and L. sativae, are polyphagous and their host range includes numerous crops.

Each leafminer female can produce several hundred eggs during its life span and lay up to ca. 40 of them per day, which are deposited singly with an ovipositor directly under the epidermis of the leaf. The larvae hatch after 2-4 days and go through three active stages which altogether last between some days and 3 weeks. For pupation, the larva leaves the leaf mine and drops to the ground. It burrows a few centimetres deep into the soil and forms a puparium. Inside it a fourth larval instar is passed before the actual pupation, which mostly lasts 1-2 weeks. The emerging males live only some days, the females, however, up to three weeks. Under favorable conditions some Liriomyza species can complete their whole life cycle in a few days. Leafminers prefer high temperatures, during cool weather development rests.

The leafminer species mentioned above originate from the Americas, but have by now spread throughout the world. In warm climates they can reproduce almost the whole year round. In temperate regions during summer they may be found in open fields, otherwise they are limited to greenhouses.

Occurrence

Additional Crop Information

Those Liriomyza spp. which are pests have a vast host range including vegetables and ornamentals from about 50 genera in several economically important plant families.

Among them are beet, broad bean, broccoli, calendula, capsicum, carnation, carrot, cauliflower, celery, chrysanthemum, cineraria, cucumber, dahlia, daisy, eggplant, flax, garlic, gerbera, hibiscus, leek, lettuce, mangold, melon, nasturtium, onion, parsley, pea, petunia, primula, pumpkin, spinach, sunflower, tagetes, tomato, verbena, viola, watermelon and zinnia.

Agricultural Importance

Due to their broad host range and ability for rapid population growth under favorable conditions, some species in this group are among the most serious pests, especially in ornamentals. Occasionally losses can reach 100%.

Control

Integrated Crop Management

Beneficial insects play an important role in limiting leafminer populations, therefore pesticides should be chosen and applied with care, as indiscriminate use may worsen the situation by disrupting natural control mechanisms. Infested plant material must be destroyed, as larvae can complete their development in detached leaves, e.g. on the greenhouse floor. Substrates should be sanitized as pupae can remain viable for several months. Fields should be disked or tilled immediately after harvest, to cover pupae and crop residues.

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