The weaver spider mite (figure 1) goes through 5 stages of development (figure 2): egg, larva, protonymph, deutonymph and adult. The duration of a cycle varies depending on the temperature: about 7 days at 30 ° C and 36 days at 15 ° C.

 

• Forms of conservation and / or alternative hosts

It is the females that have entered diapause that ensure the wintering of this mite. This diapause occurs as soon as the temperature or food drops.

• Stages of development

The eggs (1) (figure 3) are laid mainly on the underside of the leaflets. They are round, tiny (0.14 mm in diameter), translucent at first, then become opaque, and eventually turn yellow as they approach hatching. The larvae (2) (figure 4), which have 3 pairs of legs, are initially very pale, then take on a greenish tint. They have two red eye spots as well as two dark spots in the middle of their body. The protonymphs larger (3) have four pairs of legs and vary in color from light green to dark green; they also have two more contrasting spots on their body. The deutonymphs (4) are larger than the protonymphs but of the same color. It is at the stage adult (5) (figures 5 and 6) that we can distinguish males from females: the female, oval, measures 0.5 to 0.6 mm in length. Its color is variable (orange, light yellow, light green to dark green, even red). The male is more active, smaller and narrower than the female. It also has a variable color (light yellow to orange, dark yellow to brown). On tomato, T. urticae is frequently reddish.

Larvae, nymphs and adults, often present on the underside of the leaf blade, feed by biting and then sucking on the contents of plant cells. These bites, which are sometimes very numerous, are the cause of the symptoms observed.

• Dispersion in culture 

The mites present on a plant can fall to the ground and reach other plants or do so through the culture threads. They are also transported by workers, equipment and tools, or even disseminated by plants.

• Favorable development conditions

Pruned plants, smoked, and therefore more growing, are more favorable to the development of mites. Likewise, hot and dry periods are favorable to them. All the factors that are detrimental to the auxiliaries (too low temperatures, insecticide applications etc.) contribute to the spread of T. urticae .

 

Last change : 04/19/21