Efficacy of Native Entomopathogenic Nematodes in the Biological Control of Leucoma wiltshirei (Lepidoptera: Erebidae) in oak forests of Iran

Abstract

Wiltshire’s white, Leucoma wiltshirei Collenette, 1938 (Lepidoptera: Erebidae) is a major defoliator of oak forests in Iran, particularly in Fars Province. This study evaluated the efficacy of three native entomopathogenic nematodes (EPNs) Heterorhabditis bacteriophora Poinar, 1976 (Nematoda: Heterorhabditidae), Steinernema borjomiense Gorgadze et al. 2018 (Rhabditida: Steinernematidae), and Oscheius onirici (Torrini et al., 2015) (Rhabditida: Rhabditidae) for the biological control of L. wiltshirei larvae under laboratory and field conditions. Laboratory assays assessed nematode survival and infectivity in water and water–olive oil mixtures at 14 °C and 24 °C over different post-treatment intervals. The highest infective juvenile (IJ) survival (94.33%) was observed at 14 °C on day 1 in the water-based mixture with S. borjomiense, which also maintained 8.33% viability at 24 °C after 14 days. Infectivity tests demonstrated significant larval mortality, with H. bacteriophora causing 95% mortality at 14 °C on day 7 in the water–olive oil mixture. Mortality was 84% and 45% for S. borjomiense and O. onirici, respectively, under the same conditions. In field trials conducted in 2023 and 2024, nematode suspensions were applied to oak tree trunks to target overwintering larvae. Heterorhabditis bacteriophora produced the highest mortality (51.91% in 2023 and 57.15% in 2024), followed by S. borjomiense (40.21–43.12%) and O. onirici (37.05–38.85%) after 14 days. These results highlight the potential of native EPNs, particularly H. bacteriophora, as effective and environmentally sustainable agents for managing L. wiltshirei in Iranian oak forests.