An outbreak of stick insects, Ramulus mikado, as forest pests in South Korea has become a topic of concern. While other countries have reported these insects being severely affected by the entomopathogenic fungus Metarhizium spp., comprehensive research in South Korea remains limited on this topic. In our two-year investigation, we investigated the infection rate and mortality of R. mikado caused by Metarhizium anisopliae. In 2022, specimens were collected from Cheonggyesan, and in 2023 from Geumamsan. Although no infections were confirmed in the specimens collected in June of both years. Beginning in July, mortality and infection rates were greatly increased. In conclusion, the summer monsoon appears to create hot and humid conditions in the forest, contributing to reduced survival rates for these insects due to infection by M. anisopliae.

• Dong Gyu Min(Department of Forest Environment Protection, Kangwon National University, Chuncheon 24341, Korea) Corresponding author
• Seul-Ki Son(Department of Forest Environment Protection, Kangwon National University, Chuncheon 24341, Korea)
• Min Jeong Baek(National Institute of Biological Resources, Incheon 22689, Korea)
• Sun-Jae Park(National Institute of Biological Resources, Incheon 22689, Korea)
• Jong-Kook Jung(Department of Forest Environment Protection, Kangwon National University, Chuncheon 24341, Korea)