The Rosaceous longhorn beetle (RLHB), Osphranteria coerulescens Redtenbacher (Coleoptera: Cerambycidae) is a significant pests of fruit orchard in Iran and it is costly to control it. During an ongoing project on natural enemies of O. coerulescens in Mashhad region, North East of Iran, two isolates of entomopathogenic fungi (EPF) were isolated as natural pathogens on the larvae. The fungal isolates were identified based on morphological characters and then ITS gene sequences were used for inferring phylogenetic relationship. These isolates were identified as Beauveria bassiana sensu lato (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae) and Metarhizium anisopliae sensu lato (Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae). In the laboratory bioassay, potential virulence of entomopathogenic fungi against O. coerulescens larvae was conducted in various treatments. The larvae were susceptible to both EPF isolates, but the B. bassiana isolate caused significantly higher mortality than the M. anisopliae isolate. Application of EPF suspensions under special climatic conditions against in early life stages is thought to be promising for control of O. coerulescens

Keywords