Comparative efficacy of native and commercial entomopathogenic nematodes against the boxwood moth, Cydalima perspectalis: implications for biological control in Caspian boxwood forests

Abstract

Cydalima perspectalis (Walker, 1859) (Lepidoptera: Crambidae), commonly known as the box tree moth, is a highly destructive invasive pest that poses a significant threat to Buxus hyrcana Pojark. (Buxales: Buxaceae), the Caspian boxwood, in the Hyrcanian forests of northern Iran. This study evaluated the pathogenicity of three native entomopathogenic nematode (EPN) isolates (Steinernema carpocapsae, S. feltiae, and Heterorhabditis bacteriophora) and two commercial products (Capsanem and Scia-Rid) against C. perspectalis larvae, focusing on earlier instars critical for effective pest management. In laboratory bioassays, native S. feltiae achieved 100% mortality within 48 h at low concentrations (100 infective juveniles/Larvae (IJs/L) for second instar and 50 IJs/L for fourth instar larvae), with LC50 values significantly lower than those reported in prior studies, highlighting the superior pathogenicity of locally adapted strains. Notably, fourth instar larvae were more susceptible to EPN infection than second instar larvae, a novel finding that challenges conventional assumptions about larval vulnerability. Field trials confirmed the efficacy of native S. feltiae and Scia-Rid, which significantly increased larval mortality over time, while H. bacteriophora exhibited lower efficacy. These results underscore the potential of native EPNs, particularly S. feltiae, as sustainable alternatives to chemical pesticides for managing C. perspectalis. This study advances IPM strategies by demonstrating the importance of targeting-larval instars and utilizing locally adapted EPN strains, offering a promising approach for protecting forest ecosystems.

Keywords: Heterorhabditis; Steinernema; Caspian boxwood; Lethal concentration; biological control; larval mortality.