Insect Pest Suppressive Soils: Buffering Pulse Cropping Systems Against Outbreaks of Sitona Weevils

Innovative approaches to redesigning agricultural systems are urgently needed. A crucial way of 'ecologically intensifying' agricultural production relies on designing cropping systems that mimic the diversity of natural ecosystems through lengthening and diversifying crop rotations and reducing tillage intensity (e.g., conservation agriculture). Minimal soil disturbance (reduced or no tillage) and permanent soil cover (mulch) combined with rotations facilitate to conserve, improve, and make more efficient use of natural resources. These practices not only reduce soil degradation but also contribute to sustained agricultural production including biological control of pests and diseases. Plant pathologists have for a long time studied the concept of 'suppressive soils' and tried to understand the mechanisms involved in plant disease suppression. We propose to expand the concept to 'insect pest suppressive soils', and provide concepts and data on the occurrence and importance of soil-borne insect pathogens in pest population suppression. Agricultural fields usually harbor only low numbers of beneficial insect antagonists such as entomopathogenic nematodes (EPN) and fungi (EPF), so that their role in pest population dynamics currently is negligible. Yet simple improvements or modifications in field and crop management can quickly increase the numbers of EPN and EPF to levels that will impact the peak pest populations. Sitona weevils are highly susceptible to common insect pathogens, and can play a key role in maintaining effective EPN and EPF levels in the field, while being under effective control themselves.