When they feel a life-threatening scent in the air, the tiny spider mites behave very oddly: they fall asleep. A recent study shows that this effect could be used against them, in order to save crops, their main food source.

Martijn Egas and his team from the University of Amsterdam in the Netherlands observed that when the adult female spider mites feel the presence of potential predators, they look for a place to hide and enter a catatonic state which researchers call diapause. This is a kind of hibernation generally resorted to in order to ensure survival during times of severe famine, drought or extreme cold.

The two-spotted spider mites are specialized in feeding on leaves, but the intense predation during the end of the summer forces them to hide under the bark of trees or in the soil and live without food. The diapause state that they enter when they feel predator odor helps them overcome the negative effect of food deprivation and thirst by severely changing their physiology. This process decreases their population growth rate, which, in turn, may have a major impact on the prey-predator system stability and ecosystem.

The scientists placed mates in two separate wind tunnels and made so that each group of insects would be exposed to wind coming from two distinct chambers. In one of the chambers, mites were feasting peacefully from bean leaves, while in the other, they were subjected to attacks from some predator mite species. As a result, the insects exposed to winds coming from the latter chamber showed a number of diapause reactions 15% higher than the others, which demonstrated the effect of the mere predator scent.

Egas is confident that this phenomenon can be exploited in order to create a pest-controlling predator-scented perfume in the near future. This would prove even more useful given that the spider mites, scientifically called Tetranychus urticae, can't revert from the self-induced diapause to regular physiology and life for a matter of weeks. As Egas says, “If we could time the release of odours to harvest periods, we could avoid significant damage to plants”.