Quantification of the biological control of aphids by their natural enemies in sugar beet crops

• Ground-dwelling predators reduced aphid populations by up to 80%. • A high parasitism rate was detected early in the season. • Field margin could impact the activity-density of generalist predators. • For sugar beet crop, early ground-dwelling predators were key to biological control. Conservation biological control system involves a diverse community of natural enemies that significantly regulate pests in crops. However, the relative contribution of these different functional groups of natural enemies to aphid regulation is poorly known in major crop-pest systems. Moreover, there is a need to identify the timing of this contribution, especially when aphids are able to transmit pathogenic viruses to plants, such as in sugar beet crops. In this study, we quantified the effect of ground dwelling predators (carabids, spiders, rove beetles) and parasitoids on aphids’ abundance in sugar beet crops, using two experiments conducted over two successive years (2022 and 2023). Based on physical exclusion devices (pitfall traps, barriers, insect-proof cages), we showed that ground dwelling predators significantly lowered the abundance of aphids ( Aphis fabae and Myzus persicae ). Ground dwelling predators made a significant contribution to natural pest control, as they lowered aphids’ populations by up to 80%, especially as they were present early in the season. Around 48% parasitism rate was measured in 2023. Our results suggest that both groups of natural enemies appear to play a particularly important role in aphid regulation, especially ground dwelling predators. This suggests that agricultural practices, as a vegetated field margin, favouring generalist predators overwintering or colonization could lead to fewer damage and losses for farmers.