Evaluation of lucerne cover crop for improving biological control of Lyonetia clerkella (Lepidoptera: Lyonetiidae) by means of augmenting its predators in peach orchards

Abstract

The impact of cover crop manipulation on reducing reliance upon insecti-cides to control Lyonetia clerkella (L.) (Lepidoptera: Lyonetiidae), a major insect pest on peach trees, was assessed in two-year field experiments in China. Studies were conducted in three peach orchards, each with four treatments. The treatments were lucerne cover crop (L), lucerne cover crop plus limited applications of chlorbenzuron on the trees (L+L), natural ground vegetation (NG), and natural ground vegetation plus conventional applications of chlorbenzuron (NG+C). Densities of L. clerkella and predators were assessed for all treatments. L. clerkella densities were significantly lower in the two insecticide treatments (L+L, NG+C) than densities in the two treatments without insecticide applied (L, NG) in both 2003 and 2004. Densities of L. clerkella in the L+L treatment were significantly lower than densities in the NG+C treatment. Annual abundance of L. clerkella was also significantly lower in the L treatment than in the NG treatment, indicating that Lucerne ground cover led to reduced L. clerkella abundance. Predator densities in both the ground vegetation and tree canopy were significantly higher in the two lucerne-sown treatments (L, L+L) than in the two natural ground vegetation treatments (NG, NG+C). We conclude that decreased L. clerkella abundance in the lucerne-sown treatments was mainly due to an increase in predator densities. Spiders were the dominant predators and Thomisidae (hunting spiders) was the most important family. The results indicate that maintaining lucerne ground cover can attract and propagate beneficial arthropods, which in turn may lead to decreased reliance on insecticides.