Spider Mite Damage

How does such a tiny mite cause so much damage?

Some researchers estimate that spider mites account for as much as a 5% loss in total agricultural productivity worldwide. Gardeners also know that these pests can cause severe injury in a very short time. Until fairly recently, however, it was not known exactly how spider mites cause so much damage.

Spider mites feed by piercing the leaf surface with stylet-like chelicerae and extracting leaf cells and fluid. This manner of feeding causes tiny holes to be punched into the otherwise protective, water proof leaf surface.

Leaves that have been fed on by spider mites are usually dry and brittle and the usual green color is lost (right). Injured leaves are shed more quickly and eventually the whole plant may die. Even a minor spider mite infestation can have a significant impact on a plant's productivity.

Leaves normally control water loss through a system of stomates, or valves, that can be opened and closed. When the stomates are closed the surface of a leaf is highly resistant to water loss. Spider mite feeding disrupts this system by creating holes that allow water to escape. This uncontrolled water loss eventually dehydrates the leaf.

Ironically, the water stress caused by spider mite feeding actually makes the leaves a better food source because stressed leaves have higher levels of sugars and soluble nitrogen - both of which are needed by spider mites.

The articles cited below are from research done during the early 1980's on the effects of spider mite feeding on host plants.