Red spider mite

Red spider mite

What is it?

The red spider (Tetranychus urticae) is a type of mite, which is not considered as a real insect, but is classified as a type of arachnid. The adults are reddish brown (deep red during the summer), very small (about 0.5 mm long) and oval in shape. They live in colonies, especially on the lower part of the leaves, and feed on piercing the leaf tissue and sucking the vegetable fluids. Feeding signs appear as light spots on the leaves. With continuous feeding, the leaves turn yellow and can dry up. The red spider is more common in hot and dry conditions, in fact the attacks are more frequent in the summer. The host plants are varied and include strawberries, melons, beans, tomatoes, aubergines, ornamental flowers, trees and most houseplants.

Life cycle

As for reproduction, it can occur in two ways: sexed and asexual. In the first case there is a coupling between the male and the female, and the eggs will give rise to the females, while in the second case the asexual females will give birth to males directly without laying eggs. This is a big problem, because they multiply rapidly if nothing is done in time. Most species of red spider mate overwinter eggs on the leaves and / or bark of host plants. At the beginning of spring, with warm temperatures, the small six-legged larvae begin to come out of the egg and eat for a few days before seeking refuge where they change into the first stage of nymph. The nymphs have eight legs and pass through two suits before becoming mature adults. After mating, the females continuously produce up to 300 eggs over the course of a couple of weeks. The heat and dry climate favor the rapid development of these pests. During these conditions the time needed to switch from egg to adult can occur in just 5 days. There are several generations superimposed on the year.

Damage caused

These red spider mites are so small that they are barely perceptible to the naked eye. They keep alive by sucking material from plant cells, and cause visible damage to the naked eye, consisting of a series of yellow dots that are found on the leaves and by drying them. It can also produce dwarfism in growing plants. In particular: on annual vegetable crops - such as melons and watermelons - the loss of leaves can have a significant impact on yield and lead to burns; on crops like jackdaws and beans, where the pods are attached, red spider mites can cause direct damage. On ornamental plants, they are primarily an aesthetic problem, but they can kill plants if populations become very high on annual plants. Red spider mites are also important rose pests on the cultivated field.

Red spider mite: Control and disinfestation

The use of chemical pesticides actually favors the spread of these mites, because they kill their predatory insects. Mites are also known for the rapid development of resistance to various pesticides. For these reasons, it is important to control them with effective natural and biological methods. The infested plants should be thrown away to prevent the red spiders from infesting nearby plants. Useful insects such as ladybugs and mites, important natural enemies are available on the market. If the populations are high, use a less toxic pesticide of short duration to reduce infestations. Insecticidal soap, neem oil or botanical insecticides can be used to detect the treatment of heavily infested areas. On fruit trees, horticultural oil must be applied at the beginning of the season or in late autumn to destroy the eggs. The dust on the leaves, branches and fruits attracts the red spider: removing dust from the trees is a useful preventive. Water stress makes both trees and garden plants more susceptible to mite infestations. Make sure the plants are properly watered.