Liriomyza  spp.

Leafminer

General  

• Rather polyphagous * insects widely distributed in the world which are classified in the order of Diptera and the family of Agromyzidae.
• Several of these flies are classified as quarantine pests.
• Several species found on eggplant, in particular for example: Liriomyza bryoniae , Liriomyza trifolii, Liriomyza sativae , etc.
• Controlling the populations of these pests is often problematic because of their possible resistance to several insecticides, the latter also eliminating useful fauna (Hymenoptera parasitoids).
• Observed in the open field and under shelters.

* These polyphagous leafminers multiply and persist on many alternative cultivated hosts (tomato, cucumber, lettuce, melon, pepper, celery, bean, potato, chrysanthemum, gerbera), as well as on weeds present in or in outside of culture.

• Organs attacked : mainly leaves.
• Symptoms :
  • Numerous chlorotic nutritional punctures observed on the lamina and performed by females with their ovipositor. More or less sinuous galleries and mines (figures) subsequently appear on the leaves.
  • Yellowing of the most affected leaves which can wilt and dry out. The photosynthetic activity of plants, their growth and yields are thus more or less reduced.

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• Signs  : Presence of flies and larvae on and in the affected organs, and in the culture (figures).
• Possible confusion :

Biology

• Development cycle (figure): 6 stages of development are observed (egg, 3 larval stages, pupa and adult).
  • Eggs, cream-colored and oval in shape, deposited in the tissues during spawning bites using the ovipositor of females. A female can produce several hundred eggs which subsequently hatch and give birth to transparent larvae.
  • Larvae burrowing in the leaflets of the galleries which the presence of black excrements makes clearly visible. The white third instar larvae pierce the leaf blade, leave the leaflets, drop into plastic folds or onto the ground, and bury themselves shallowly.
  • Subsequently, they turn into barrel-shaped pupae and vary in color as they age from yellow to dark brown, blackish pupae are often the ones that are parasitized.
  • Adults, small flies 2-3 mm long, yellow and black ( Liriomyza spp.) Or blackish gray (C hromatomyia horticola ). The adult females, present on the upper surface of the limbus, perforate the epidermis thanks to the real auger that is their ovipositor, suck the vegetable juice (nutritional bite) and deposit their eggs (egg-laying bites). Note that the males, devoid of augers, also take advantage of the feeding bites to feed themselves.
• The duration of their cycles varies according to temperature and species.
• Adults are easy to fly and disperse in cultures and their environments. Newly contaminated plants (carriers of eggs or very young mines) can also contribute to the spread of these insects.
• The evolution of the population levels of these insects is rather influenced by high light intensities, certain rather vigorous host plants, high humidity (80-90%) in particular.

Protection

• Disinfect the reused substrate or soil.
• Weed the greenhouse and its surroundings.
• If possible, produce the plants in an shelter insect-proof . The use of insect nets can protect the nursery, but also the crop.
• Control the sanitary quality of the plants.
• Place yellow sticky panels under shelters in order to capture the adults, preferably positioning them above the crop to increase the probability of capture.
• Collect and destroy heavily mined leaves, and remove and destroy crop residues.
• Favor natural enemies in field crops or under open shelters.
• Use biopesticides.
• Reason for chemical protection, in particular if you use auxiliaries or biopesticides. This is not always effective and should preferably be combined with cultural, physical and organic methods. The repeated use of insecticides can lead to resistance phenomena in leaf miners, rendering the active ingredients ineffective in the short term.