Leafminers have 6 stages of development during their cycle (Figure 1): egg, 3 larval stages, pupa and adult.

• Forms of conservation and / or hosts  

Few adults are observed during the winter because of the entry into diapause of the pupae. Since these leafminers are polyphagous, they can 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 outside the culture.

• Stages of development

The eggs (figure 3-1), cream-colored and oval in shape (those of Liriomyza bryoniae measure 0.12 x 0.27 mm), are deposited in the tissues during the spawning bites using the ovipositor females. A female can produce several hundred eggs which subsequently hatch and give birth to larvae transparent and 0.5 mm long (Figure 3-2) (Figure 2). These dig galleries in the leaflets that the presence of black excrement makes clearly visible. The 2.5 mm long, third instar white larvae pierce the blade, leave the leaflets, drop into plastic folds or onto the ground, and bury shallowly. Subsequently, they transform into pupae (Figure 3-3) barrel-shaped and vary in color as they age from yellow to dark brown (Figures 3 and 4), blackish pupae are often the ones that are parasitized. The pupation of Chromatomyia horticola takes place in the leaf: the puparium, covered by the epidermis of the leaf, is then visible in the form of a small protuberance at the end of the larval gallery. The adult (Figure 4-4) are small flies of 2 to 3 mm long, yellow and black ( Liriomyza spp., 5) or dark 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 cycle varies according to the temperature; for Liriomyza bryoniae for example, it is 41 days at 15 ° C and passes to 17 days at 25 ° C, the values ​​for the other species remain the same, with the exception, however, of L. trifolii more or less which would be more sensitive to low temperatures. The lifespans of females at these temperatures are 14 and 7 days, respectively.

• Dispersion in culture

The adults fly easily in the greenhouse, even from greenhouse to greenhouse, and thus disperse in the crop (s). Newly contaminated plants (carriers of eggs or very young mines) can also contribute to the spread of these insects.

• Favorable development conditions

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.

Leafminers are generally heavily parasitized, mainly by the Hymenoptera chacidiens. Insecticide treatments, sometimes unjustified, are very damaging to this useful entomofauna, and are often responsible for the outbreaks observed.

Last change : 04/19/21