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Spider mites

The tiny red colored spider mites are plant-feeding mites and feared pests on several crops all over the world. In dry, warm weather a spider mite population can grow very rapidly.

Damage

Red spider mites suck plant sap for food. Plant cells turn yellow, which can be seen on the upper surface of the leaf as small yellow spots. This reduces the photosynthetic area of the leaf and the plant gets out of physiological balance. Moreover, the webs made by spider mites reduce the aesthetic value of ornamentals.

Description and life cycle

The female deposits round eggs of about 0.14 mm on the underside of the leaf. Out of the egg a colorless larva with 6 legs hatches and immediately starts feeding. Subsequently, the larva develops into a protonymph, a deutonymph and an adult stage. The nymphs are light to dark green and have 2 clearly developed body spots. The color of the adults can vary from yellow-brown to red-brown, depending of the crop on which they occur. Both males and females have 2 large dark body spots. The development stages are separated by a resting stage, during which the mite settles immobile on the leaf. Once the mite has become adult, it takes another 0.5 to 3 days before the female starts laying eggs. The total development time takes 7 days at 30°C (86°F), 17 days at 20°C (68°F) and 36 days at 15°C (59°F). The female lays her eggs dor 10 days (at 35°C or 95°F) and up to 40 days (at 15°C or 59°F). At 20°C (68°F) she lays about 40 eggs in total, but under optimal circumstances this can mount up to 100. Especially during dry and warm weather spider mites can reproduce very rapidly. In autumn, when temperature and photoperiod drop, fertilized females enter diapauses. Such females turn orange-red. They hide in all kinds of cracks in the greenhouse, to appear again early in the following season when circumstances improve.

Species

The most common species are two spotted spider mite (Tetranychus urticae) and the carmine spider mite (Tetranychus cinnabarinus).

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