• Definition
  Mites belong to the class Arachnids. Adults have four pairs of legs, unlike insects which have only three. It should be noted that a few species attack tomatoes, including Tetranychus urticae , which is the most widely reported mite on this crop. Also called “tetranic weaver” because of the webs it forms on plants, it is cosmopolitan, common and very polyphagous since it is reported on nearly 2,000 plant species.

  This mite can be responsible for significant damage, or even rapid infestations, especially in undercover. Cases of resistance to miticides have been reported on several occasions in this mite. Other species of phytophagous Tetranychidae , as well as predatory mites Phytoseiidae, can occasionally be found on tomatoes.

  Development Lifecycle
  The life cycle of dust mites goes through 5 stages:

  • Eggs (stage 1) 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 end up turning yellow as they approach hatching.
  • The larvae (stage 2), which have 3 pairs of legs, are very pale at first, then take on a greenish tint. They have two red eye spots as well as two dark spots in the middle of their bodies.
  • The protonymphs (stage 3), which are larger, have four pairs of legs and their colour varies from light to dark green; They also have two more contrasting spots on their bodies.
  • Deutonymphs (step 4) are larger than protonymphs but of the same color.
  • It is at the adult stage (stage 5) that we can distinguish males from females: the female, oval, measures 0.5 to 0.6 mm in length. Its colour is variable (orange, light yellow, light green to dark green, or even red).
  • The male (stage 5) is more active, smaller and narrower than the female. It also has a variable color (light yellow to orange, dark yellow to brown). On tomatoes, T. urticae is frequently reddish.

  Symptoms

  • They suck the sap out of the leaves, which causes them to turn yellow and take on a brown, silvery or tan colour; the leaves dry out and then fall off.
  • Flower Abortion
  • The fruits remain small and ripen poorly; The green fruits remain smaller, take on a bronzed, corky and cracked appearance.
  • The plant may wilt and die.
  • Due to the very small size of the mites, we only realize their presence once the first damage has already been done.

  Contributing factors

  • Pruned plants are more favourable to the development of mites.
  • High temperatures, hot and dry periods are conducive to them.
  • Absence of rain and humidity
  • High plant density
  • Presence of weeds on the plot

Recommended Prophylactic and Cultural Method

• Avoid cultivating contaminated plants.
• Weeding of greenhouses or the plot and the surrounding area.
• Regular observation and monitoring of the plot.
• Aeration and misting are necessary.
• Biological control through the use of mite predators such as the midge Feltiella acarisuga or auxiliaries such as Phytoseiulus persimilis and Amblyseius californicus.

Chemical method

• Favor preventive treatment.
• Observation of the different stages of development under a magnifying glass in order to choose the type of product to be applied (ovo-larvicides, adulticides, etc.).
• To prevent addiction or resistance, use applications based on products belonging to different chemical families and modes of action.

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