Enhancing biological control by ground beetles (Coleoptera: Carabidae) through agricultural drainage ditch management practices

Conservation biological control seeks to mitigate pest damage by enhancing natural enemies on farms. Agricultural drainage ditches are underutilized field margin habitats that hold high plant and arthropod biodiversity that may support beneficial insects. For example, ground beetles (Coleoptera: Carabidae) are widespread generalist predators that feed on economically important insect pests. Our objectives are (1) to quantify the diversity and abundance of carabids in ditches, and (2) to compare the effects of ditch management practices, including delaying mowing until spring and applying straw along ditch banks in fall, on carabid communities. To do this, ground-running carabid activity-density was measured using pitfall traps along a drainage ditch in summer 2020 as a control. The ditch was divided lengthwise into 16 plots, each assigned one of four treatments in a randomized block design. Treatments were applied in the fall and spring over the following two years, and carabid activity-density measurements were repeated in summers 2021 and 2022. We observed a diverse community of carabids within the ditch, including adults of 15 genera and larvae of 5 genera, indicating use of the drainage ditch as a reproductive site. In 2022, total carabid activity-density was 97% greater in plots treated with straw. This trend was dominated by two of three collected species of autumn-breeding carabids which overwinter as larvae, implying that these treatments may aid larval survival. Results of this study can be used to provide farmers with novel management practices for increasing the activity of natural enemies and reducing pest damage.