What are two-spotted spider mites?
Two-spotted spider mite (Tetranychus urticae) is a pest of many crops throughout the world. Despite their small size, they are capable of very rapidly doing severe damage, due to their great reproductive capacity. There are more than 1200 species worldwide and many of them are major crop pests. The two-spotted spider mite (Tetranychus urticae) is by far the most important species in greenhouses and many outdoor crops.
Life cycle of two-spotted spider mite
Two-spotted spider mites are small and have eight legs. Adult females are about 0.5 mm long. They have an oval body that is rounded at the rear end. Their colour can vary from orange, light yellow or light green, to dark green, red, brown, or almost black.
Males are smaller and more active than the females, with a body that is narrower and more pointed at the rear. Colour is very variable: from light yellow or orange to dark yellow or brown.The colour of the adults often depends on the crop in which they occur (e.g. on cucumbers they are often yellow-brown, on tomatoes they are mainly red-brown).
Both males and females usually have two large black spots, giving rise to the common name, “two-spotted spider mite”. The spots can vary in both form and size. The red eyes can be seen in all stages.
Recognize two-spotted spider mite
Spider mites can be identified by the following characteristics:
- Size and shape: Spider mites are tiny, adults are about 0.5 mm long in length. They have an oval-shaped body with eight legs, which distinguishes them from insects that have six legs.
- Color: Spider mites can have a variety of colors, including green, yellow, red, brown, or black. Two-spotted spider mites have two large dark spots on their body.
- Movement: Spider mites are slow-moving and tend to cluster on the undersides of leaves, where they feed on plant sap. They produce fine webbing over the infested area.
- Damage: Spider mites can cause damage to leaves by piercing the plant cells and sucking out the contents. This can result in yellowing, speckling, or browning of the leaves. Severe infestations can cause the leaves to dry up and fall off the plant.
Spider mite damage
Larvae, nymphs and adults cause damage to the host plant by feeding on plant sap. They mainly occur on the underside of leaves where they pierce the cells and suck out the contents. The empty dead cells become yellow, and in many plants the damage can also be seen on the upper surface of leaves as small yellow dots. The destruction of cells results in reduced photosynthesis, increased transpiration and reduced plant growth. As damage increases, whole leaves turn yellow, and as more cell sap is removed, the leaf, and eventually the whole plant, may die. In tomatoes and cucumbers, as little as 30% damage of the leaf surface can lead to loss of the crop. The nymphs and adults also produce webs, and plants can get completely covered with such webs in which the mites live. The webbing and spotting on the leaves affects the appearance of the crop. This is of particular concern in ornamental crops.
How to prevent spider mite
Preventing spider mites in your crop involves several strategies. Firstly, it is important to maintain good plant health through regular irrigation and fertilization, as stressed plants are more susceptible to spider mite infestations. Additionally, ensure that spider mites cannot enter your greenhouse by implementing hygienic measures. Moreover, it is essential to monitor your crop regularly for signs of spider mites, so you can detect an infestation early and take action. This can be done by visually scouting the plants.
Finally, introducing biological control agents such as predatory mites can be an effective preventative measure, as these natural enemies can help keep spider mite populations in check. Especially predatory mites in sachets are a good preventative measure as the sachets enable a continuous supply of predatory mites even before the pest is present.
Biological control of spider mite
Biological control is a popular and effective method for managing spider mite populations in agriculture. Predators such as predatory mites, predatory bugs and gall midges are often used to control spider mites. These natural enemies can be released in the affected area of the crops, where they will feed on spider mites, reducing their populations.
The predatory mite Phytoseiulus persimilis (Spidex, Spidex Vital, Spidex Vital Plus), by far the most important natural enemy of Two-spotted spider mite (Tetranychus urticae), is used in many crops worldwide. The predatory mite Neoseiulus californicus (Spical, Spical-Plus, Spical Ulti-Mite), is more tolerant to higher temperatures, lower humidity and synthetic pesticides than Phytoseiulus persimilis.
The gall midge Feltiella acarisuga (Spidend) can be introduced to control hot spots, I.e. large, concentrated spider mite populations.
A combination of different natural enemies usually provides best control.