Spider mites perform worse on soil microbe-inoculated plants: from the lab to the greenhouse

Abstract: Spider mites are key pests in several crops causing significant yield losses.
Specifically, the two spotted spider mite Tetranychus urticae, is a polyphagous pest which is
usually controlled in Integrated Pest Management (IPM) schemes with biological control i. e.,
the release of predators and application of chemicals. In this context, beneficial soil microbes
are applied as biofungicides or plant growth promoting agents. Herein, we explored the plantmediated effects of a series of beneficial soil fungi and bacteria on spider mites infesting tomato plants aboveground. Experiments were conducted in the lab to assess short-term effects on spider mite performance. Subsequently, promising microbes were assessed for their effects on the population dynamics of the mites with greenhouse experiments. Our results show that inoculating tomato plants with microbes can result in decreased spider mite performance both in the short- and the long-term. Furthermore, biological control with the release of the zoophytophagous predator Macrolophus pygmaeus resulted in a stronger reduction in the number of spider mites and eggs, in inoculated plants. Overall, our study highlights the role of beneficial soil microbes in shaping plant-mite interactions to the benefit of the plant.