Non-invasive techniques for investigating and modelling root-feeding insects in managed and natural systems

Root-feeding insects are now considered to play a greater role in ecosystem processes than previously thought, yet little is known about their specific interactions with host plants compared with above-ground insect herbivores. Methodological difficulties associated with studying these insects in the soil, together with the lack of empirical and theoretical frameworks, have conventionally hindered progress in this area. This paper reviews recent empirical and theoretical developments that have been adopted for studying root-feeding insects, focusing on the non-invasive techniques of X-ray tomography and acoustic field detection and how these can be integrated with new mathematical modelling approaches. X-ray tomography has been used for studying the movements of several insects within the soil and has helped to characterize the host plant location behaviour of the clover root weevil, Sitona lepidus. Acoustic detection of soil insects has been used in various managed systems, ranging from nursery containers to citrus groves. Mathematical modelling plays a complementary role for investigating root-feeding insects, illustrated by a number of published models. A model is presented for the movement of S. lepidus in the soil, which suggests that these insects undergo Lévy movements, similar to those recently demonstrated for above-ground organisms. The future directions and challenges for investigating root-feeding insects are discussed in the context of the wider ecosystem, incorporating both above and below-ground organisms.