Influence of soil tillage on natural regulation of the cabbage root fly Delia radicum in brassicaceous crops

Abstract

Ground dwelling predators provide regulation services of several insect pests. Enhancing these services may be a step toward integrated crop protection. Many studies have shown that soil tillage is deleterious to ground dwelling predators but pest regulation processes and services have rarely been measured. We performed an experiment to study whether simplifying soil tillage before the establishment of spring broccoli enhanced ground dwelling predator populations and the control they provide on Delia radicum. The direct effect of tillage on arthropods was assessed by comparing their emergence rates in plots differing in soil tillage management. The natural regulation service was assessed by comparing a control and an exclusion treatment in which predators were removed. The effect of soil tillage on carabids, spiders and staphylinids did not match the gradient of disturbance induced by tillage treatments. Tillage did not appear to affect the predators that likely contribute to D. radicum regulation. Consistently, the number of pests suppressed and the root injuries were unaffected by tillage treatments. The main deleterious effect of soil tillage was on the emergence of those carabid species that overwinter partly as larvae, suggesting that spring tillage could affect pest control in the following crops.