Developing Soil Microbial Inoculants for Pest Management: Can One Have Too Much of a Good Thing?

Soil microbes present a novel and cost-effective method of increasing plant resistance to insect pests and thus a sustainable opportunity to reduce current pesticide application. However, the use of microbes in integrated pest management programmes is still in its infancy. This can be primarily attributed to the variations in microbial inoculum performance in laboratory and field conditions. Soil inoculants containing single, indigenous microbial species have shown promising results in increasing chemical defences of plants against foliar feeding insects. Conversely, commercial inoculants containing multiple species tend to show no effects on herbivore infestation in the field. We present a simple model that endeavours to explain how single and multiple species in microbial inoculants differentially govern insect population dynamics via changes in plant chemical profiles. Furthermore, we discuss how this knowledge can be applied to manipulate soil microbial species and develop ‘tailored’ microbial inoculants that could be used in plant protection against antagonists.