Understanding biological control function and trophic interaction dynamics of an artificially released predatory bug by DNA metabarcoding

Understanding the dietary habits of generalist invertebrate predators in agroecosystems helps improve ecosystem programs, particularly for integrated pest management. Augmentation biological control, one of three widely accepted biological pest control methods, involves releasing a large number of natural enemies to quickly reduce damaging pest populations. However, the effectiveness of these natural enemies against target pests and their effects on nontarget pests in agricultural landscapes remain unknown. This study aimed to investigate the dietary composition of Sycanus bifidus, a generalist predator of the assassin bug that is artificially released into citrus orchards, and uncover its trophic structure across various pest species using metabarcoding-based molecular gut content analysis. We detected 30 different prey taxa from 8 orders and 19 families in 108 samples of S. bifidus recaptured over 22 d. Lepidoptera (9) made up 30% of their diet, followed by Coleoptera (5), Hemiptera (5), and Hymenoptera (5). Euproctis varians, a major lepidopteran citrus pest, was frequently found in the gut of S. bifidus with a high incidence and relative read abundance, suggesting its potential as an effective biological control agent for E. varians in citrus crops. Additionally, our findings showed that the choice of primer pair critically influenced the efficiency of diet detection, with the Fwh primer set being ideal for targeting highly degraded DNA in insect guts. This study demonstrated that metabarcoding is a valuable tool for studying predator diets, reconstructing trophic interactions in agricultural landscapes, optimizing pest management strategies, and identifying effective biological control agents.